Q. Is high-fructose corn syrup bad for you?

By Joyce Hendley,

A. High-fructose corn syrup (HFCS) is a manmade sweetener that’s found in a wide range of processed foods, from ketchup and cereals to crackers and salad dressings. It also sweetens just about all of the (regular) soda Americans drink. HFCS used in foods is between 50 to 55 percent fructose—so chemically, it’s virtually identical to table sugar (sucrose), which is 50 percent fructose. Metabolic studies suggest our bodies break down and use HFCS and sucrose the same way.

Yet, after HFCS began to be widely introduced into the food supply 30-odd years ago, obesity rates sky rocketed. And because the sweetener is so ubiquitous, many blame HFCS for playing a major role in our national obesity epidemic. As a result, some shoppers equate HFCS with “toxic waste” when they see it on a food label. But when it comes right down to it, a sugar is a sugar is a sugar. A can of soda contains around nine teaspoons of sugar in the form of HFCS—but, from a biochemical standpoint, drinking that soda is no worse for you than sipping home-brewed iced tea that you’ve doctored with nine teaspoons of table sugar or an equivalent amount of honey.

Even Barry Popkin, Ph.D. at the University of North Carolina at Chapel Hill who previously suggested, in an influential 2004 paper, a possible HFCS-obesity link, stresses that the real obesity problem doesn’t lie just with HFCS. Rather, it’s the fact that sugars from all sources have become so prevalent in our food supply, especially in our beverages. He scoffs at the “natural” sweeteners sometimes added to upscale processed foods like organic crackers and salad dressings. “They all have the same caloric effects as sugar,” he explains. “I don’t care whether something contains concentrated fruit juice, brown sugar, honey or HFCS. The only better sweetener option is ‘none of the above.’”

Comments:

People everywhere are finally waking up to the indisputable fact that all simple sugars are not the same when it comes to the physical end results they create. The latest Public Service Announcement warning New Yorkers about the dangers of excessive soda consumption is a powerful illustration of this increasing level of awareness.
When these differences are understood, it's easy to see how and why fructose—mainly in the form of high fructose corn syrup (HFCS)—is in large part responsible for the meteoric rise of obesity and its related health problems.
It's a staple ingredient in a vast majority of sweetened beverages and processed foods of all kinds, from pre-packaged meals to baked goods and condiments. And the number one source of calories in America is soda, in the form of HFCS!
Your Brain Reacts to Fructose and Glucose in Very Different Ways
This latest study is intriguing, as it shows that the difference between fructose and glucose is not just limited to how they're metabolized in your body; your brain also reacts to these two sugars in entirely different ways.
Nine healthy, normal-weight subjects received either glucose, fructose, or saline (as the control). Their brains were then scanned to evaluate activity around the hypothalamus, which is a key player in appetite control and production of metabolic hormones.
Interestingly, the researchers discovered that the "cortical control areas" surrounding the hypothalamus responded very differently to each substance:
• Glucose significantly raised the level of neural activity for about 20 minutes
• Fructose reduced neural activity in the area for about the same amount of time
• Saline had no effect on neural activity
So, what does this mean?
At this point, the implications of these differences are unclear. The Chicago Tribune reported that:
"At this point, said [lead researcher] Purnell in a phone interview, it means nothing more than that the two substances did prompt different responses in the brain--that the brain did not respond to them identically.
Within some of the "cortical control areas" where differences were seen, lie some important neural real estate, including regions where notions of reward and addiction are processed.
As scientists have a closer look in future studies, they should be able to zero in on which specific areas are affected differently by the two forms of sugar."
So, time will tell what these latest findings really mean, but we already know that fructose has a detrimental impact on two hormones involved with satiety and hunger, namely leptin and ghrelin, and that this influence sets in motion a vicious cycle of hunger, increased food intake, and increased fat storage.
Fructose Packs on the Pounds Faster than Any Other Nutrient
Part of what makes HFCS so unhealthy is that it is metabolized to fat in your body far more rapidly than any other sugar. The entire burden of metabolizing fructose falls on your liver, and it promotes a particularly dangerous kind of body fat, namely adipose fat. This is the fat type of fat that collects in your abdominal region and is associated with a greater risk of heart disease.
Additionally, because most fructose is consumed in liquid form (i.e. soda and sweetened beverages of all kinds), its negative metabolic effects are magnified. Because while HFCS has about the same amount of fructose as cane sugar, the fructose in HFCS is in its "free" form and not attached to any other carbs.
The fructose in fruits and in cane sugar is bonded to other sugars which results in a decrease in its metabolic toxicity.
Consuming foods that contain high amounts of fructose—even if it's a natural product—is, to put it bluntly, the fastest way to trash your health. Among the health problems you invite with a high-fructose diet are:
• Obesity, insulin resistance, metabolic syndrome and type 2 diabetes
• Elevated triglycerides and LDL (bad) cholesterol levels
• Elevated blood pressure
• Liver disease
• Depletion of vitamins and minerals—Unbound fructose, found in large quantities in HFCS, can interfere with your heart's use of minerals such as magnesium, copper and chromium.
• Cardiovascular disease, arthritis, gout, and cancer
Adding insult to injury, HFCS is most often made from genetically modified (GM) corn, which is fraught with its own well documented side effects and health concerns, from an increased risk of developing food allergies to the risk of increased infertility in future generations.
Beware: Mixing Fructose with Glucose Increases Destructive Effect
Fructose consumption clearly causes insulin resistance whereas straight glucose does not. However, it's worth knowing that glucose accelerates fructose absorption! So when you mix glucose and fructose together, you absorb more fructose than if you consumed fructose alone...
This is an important piece of information if you are struggling to control your weight.
Remember, sucrose, or table sugar, is exactly this blend -- fructose plus glucose. So, the key to remember is to not get too nit-picky about the names of the sugars. ALL of these contribute to decreased health:
• Sucrose (table sugar)
• Corn syrup
• High fructose corn syrup (HFCS)
• Crystalline fructose, and any other high-fructose sweetener they may dream up
• Natural fructose in the form of fruits, fruit juices, and natural sweeteners such as honey and agave.
Is Fructose from HFCS Worse than Fructose from Table Sugar?
High fructose corn syrup is about 55 percent fructose while table sugar is about 50 percent. The fructose in the corn syrup is also dissociated from the glucose, unlike table sugar which has it attached. So HFCS is clearly worse than table sugar, but not orders of magnitude. It is only marginally worse.
The MAIN reason why fructose and HFCS are so bad is that in the mid 70s two things happened. Earl Butz changed the US Agriculture policy to massively subsidize corn production in the US, and scientists also figured out how to make HFCS in the lab from corn.
The combination of these two events made fructose VERY cheap. So cheap that it's put in virtually all processed foods because it is virtually free and massively improves the flavor of most foods. So if you are a processed food producer there are virtually no downsides.
So it becomes a QUANTITY issue, and the average person is now consuming 600 percent more than their ancestors did, and some are consuming 1500 percent more. So the massive increase in this toxin is what is causing the problem. If table sugar was as cheap and used as much it would cause virtually identical side effects.
Fructose Metabolism Basics
Without getting into the very complex biochemistry of carbohydrate metabolism, it is important to understand how your body processes glucose versus fructose. Dr. Robert Lustig, Professor of Pediatrics in the Division of Endocrinology at the University of California, has been a pioneer in decoding sugar metabolism. His work has highlighted some major differences in how different sugars are broken down and used.
Here's a summary of the main points:
• After eating fructose, 100 percent of the metabolic burden rests on your liver. With glucose, your liver has to break down only 20 percent.
• Every cell in your body, including your brain, utilizes glucose. Therefore, much of it is "burned up" immediately after you consume it. By contrast, fructose is turned into free fatty acids (FFAs), VLDL (the damaging form of cholesterol), and triglycerides, which get stored as fat.
• The fatty acids created during fructose metabolism accumulate as fat droplets in your liver and skeletal muscle tissues, causing insulin resistance and non-alcoholic fatty liver disease (NAFLD). Insulin resistance progresses to metabolic syndrome and type II diabetes.
• Fructose is the most lipophilic carbohydrate. In other words, fructose converts to activated glycerol (g-3-p), which is directly used to turn FFAs into triglycerides. The more g-3-p you have, the more fat you store. Glucose does not do this.
• When you eat 120 calories of glucose, less than one calorie is stored as fat. 120 calories of fructose results in 40 calories being stored as fat. Consuming fructose is essentially consuming fat!
• The metabolism of fructose by your liver creates a long list of waste products and toxins, including a large amount of uric acid, which drives up blood pressure and causes gout.
• Glucose suppresses the hunger hormone ghrelin and stimulates leptin, which suppresses your appetite. Fructose has no effect on ghrelin and interferes with your brain's communication with leptin, resulting in overeating.
So, if anyone tries to tell you "sugar is sugar," they are way behind the times. As you can see, there are major differences in how your body processes each one. The bottom line is: fructose leads to increased belly fat, insulin resistance and metabolic syndrome -- not to mention the long list of chronic diseases that directly result.
If you, like so many others, have struggled with your weight for years; examined your diet; avoided fat and counted your calories, yet not getting anywhere and wondering what you're doing wrong, please pay very close attention to this issue!
In many cases the primary culprit is an excessive intake of hidden sugar in the form of fructose, whether natural fructose (such as agave syrup or 100 percent fruit juice, for example), or in the form of corn syrup (or high fructose corn syrup), which is a main ingredient in countless beverages and processed, pre-packaged foods.
It's extremely easy to consume high amounts of fructose on a daily basis, especially if most of your foods are processed in any way, or if you drink sodas or any other sweetened beverages such as ice-teas, fruit juices and sports drinks. As previously discussed, even seemingly "health-conscious" beverages like Vitamin Water, Jamba Juice and Odwalla SuperFood contain far more added sugar and/or fructose than many desserts!
So please, understand that it's not dietary fat that's making you fat. It's fructose.
My Recommended Fructose Allowance
As a standard recommendation, I strongly advise keeping your TOTAL fructose consumption below 25 grams per day.
For most people it would also be wise to limit your fructose from fruit to 15 grams or less, as you're virtually guaranteed to consume "hidden" sources of fructose if you drink beverages other than water and eat processed food. Remember, the average 12-ounce can of soda contains 40 grams of sugar, at least half of which is fructose, so one can of soda ALONE would exceed your daily allotment.
Fifteen grams of fructose is not much -- it represents two bananas, one-third cup of raisins, or two Medjool dates. In his book, The Sugar Fix, Dr. Johnson includes detailed tables showing the content of fructose in different foods -- an information base that isn't readily available when you're trying to find out exactly how much fructose is in various foods. I encourage you to pick up a copy of this excellent resource.
Here's a quick reference list of some of the most common fruits that you can use to help you count your fructose grams:
Fruit Serving Size Grams of Fructose
Limes 1 medium 0
Lemons 1 medium 0.6
Cranberries 1 cup 0.7
Passion fruit 1 medium 0.9
Prune 1 medium 1.2
Apricot 1 medium 1.3
Guava 2 medium 2.2
Date (Deglet Noor style) 1 medium 2.6
Cantaloupe 1/8 of med. melon 2.8
Raspberries 1 cup 3.0
Clementine 1 medium 3.4
Kiwifruit 1 medium 3.4
Blackberries 1 cup 3.5
Star fruit 1 medium 3.6
Cherries, sweet 10 3.8
Strawberries 1 cup 3.8
Cherries, sour 1 cup 4.0
Pineapple 1 slice
(3.5" x .75") 4.0
Grapefruit, pink or red 1/2 medium 4.3
Fruit Serving Size Grams of Fructose
Boysenberries 1 cup 4.6
Tangerine/mandarin orange 1 medium 4.8
Nectarine 1 medium 5.4
Peach 1 medium 5.9
Orange (navel) 1 medium 6.1
Papaya 1/2 medium 6.3
Honeydew 1/8 of med. melon 6.7
Banana 1 medium 7.1
Blueberries 1 cup 7.4
Date (Medjool) 1 medium 7.7
Apple (composite) 1 medium 9.5
Persimmon 1 medium 10.6
Watermelon 1/16 med. melon 11.3
Pear 1 medium 11.8
Raisins 1/4 cup 12.3
Grapes, seedless (green or red) 1 cup 12.4
Mango 1/2 medium 16.2
Apricots, dried 1 cup 16.4
Figs, dried 1 cup 23.0

The Way Toward Better Health Begins Here...
There is nothing benign about the fructose consumption inherent in our modern diet. It is literally supercharged with fructose, and we're seeing the consequences of this type of eating in our skyrocketing rates of obesity, diabetes, heart disease, and cases of non-fatty liver disease.
Fortunately, there's plenty of good news here.
There IS a way out of this evil circle, and that is a return to a more holistic diet based on whole foods, along with physical exercise and safe sun exposure to optimize your vitamin D levels.
One of the easiest things you can do to quickly improve your health is to eliminate all soda and sweetened beverages from your life. I say ALL soda, because even though HFCS is clearly something you want to avoid, it is still not as bad as artificial sweeteners, which damage your health even more rapidly than HFCS.
Then, since most processed foods also contain HFCS, avoiding as many processed foods as possible is your next step.
If you want an occasional sweetener, I recommend using:
1. The herb stevia
2. Dextrose (pure glucose)
I do not recommend agave syrup since it is a highly processed sap that is almost all fructose. It is one of the more seriously mismarketed foods in the natural food world. We actually did an informal study and found the most popular agave brands ranged from 59 to 67 percent pure fructose, far worse than HFCS.
Once you realize the hazards of fructose and begin to avoid it in earnest, your diet will significantly improve, which is an essential factor for a long, healthy life.

Dan

One of the principal arguments food corporations have used to defend high-fructose corn syrup (HFCS) is that it is chemically similar to table sugar.
Manufacturers have stated repeatedly that HFCS contains at most 55 percent fructose, little different from white sugar's 50 percent fructose makeup.
But as it turns out, the specific amount of fructose in HFCS for any particular food product has never been officially tested. And when researchers tested brand-name sodas, they found that the fructose content is actually 65 percent.
"Why is this important?
It's because research has shown fructose to be particularly harmful to human health. Unlike excess glucose, which passes through our digestive tract and is excreted, 100 percent of fructose that's consumed is taken up by the liver. Once there, fructose causes increased fat deposition in the abdominal cavity and increased blood levels of triglycerides -- both of which are risk factors for heart disease and diabetes."

Glucose and fructose are both simple sugars, but scientists have long suspected there are differences in the way your body processes them.
In a new study, researchers scanned the brains of nine subjects after they got an infusion of equal volumes of glucose, fructose or saline. The brain scans were looking at activity in the hypothalamus, a part of the brain which plays a key role in setting appetite levels and controlling production of metabolic hormones.
According to the Chicago Tribune:
“The researchers ... found that ‘cortical control areas’ -- broad swaths of gray matter that surrounded the hypothalamus -- responded quite differently to the infusion of fructose than they did to glucose. Across the limited regions of the brain they scanned ... glucose significantly raised the level of neural activity for about 20 minutes following the infusion. Fructose had the opposite effect, causing activity in the same areas to drop and stay low for 20 minutes after the infusion.”
Sources:
Chicago Tribune February 10, 2011

Triple your metabolism with double-dip circuits

Leave fat biting the dust with these intense circuits that work your body from head to toe to burn hundreds of calories in minutes

Workout 1: In the gym

Perform each move for 20sec, before progressing to the next exercise with as little rest as possible. Take a 40sec break at the end of the circuit, then repeat the routine once more.

1. Goblet squat

If your desk job has left your core weaker than a Greek recovery plan, try this. Hold a dumbbell against your chest, palms up, and squat. U-turn to standing.

2. Press-up with dumbbell row

Because standard press-ups are far too easy. Holding dumbbells on the floor, do a press-up and, at the top, row the right one to your chest. Alternate sides each time.

3. Alternating reverse lunge

Holding two dumbbells as shown, step backwards until your knee brushes the floor. Power through your heel to rise up. This builds strength and stability in your legs.

4. Kettlebell swing

Keep your abs engaged to turn this move into a serious calorie-melter. Bend at the waist and thrust your hips to drive and swing the kettlebell to chest height. Repeat.

5. Spider-man crawl

Make like Peter Parker and drop into a press-up. Step your right leg forwards; place your foot close to your elbow. Now push off your left foot and ‘crawl’ forwards.

6. Inverted row

Grab a barbell in a power rack with an overhand grip and extend your arms fully. Pull your chest up to the bar explosively, then lower. Make the most of that rest period.

Workout 2: At home

No gym membership? No problem – this circuit proves you don't need expensive equipmet to burn serious calories. Following similar patterns to the gym circuit, this sequence uses natural movements to rope in all your major muscle groups and work your metabolism hard.

As before, perform each exercise in turn for 20sec, then move on with no rest. Take a 40sec rest once you've completed the entire circuit, then repeat all of the exercises once more.

1. Jump squat

This will deliver Homeland levels of tension in your glutes and quads. Squat, then immediately jump up as high as you can. Land, squat and repeat the move

2. 'T' Formation press-up

Perform a press-up, then as your body rises, roll to the left so your weight rests on the outside of your left ankle. Raise your arm, hold, then repeat to the right, Mr T.

3. Alternating reverse lunge

Grab some dumbbells and lock your core like you’re about to go toe-to-toe with Anthony Joshua. Step back until your knee is close to the ground. Repeat on the other side.

4. Single-leg glute bridge

Tired? Time for a lie down, but not to rest. Bend your knees and raise your hips. Slowly extend one leg until completely straight. Return and repeat on the other side.

5. Forwards and backwards crawl

Do the Spider-Man Crawl, but this time reverse the move after crawling forwards. You'll benefit from a rigid core and Peter Parker-esque spatial awareness.

6. Standard chin-up

Grab a pull-up bar, arms straight. Pull up explosively until your chin is above the bar. Lower slowly and avoid dropping from the bar like Drogba looking for a penalty.

Does Thinking Really Hard Burn More Calories?

Does Thinking Really Hard Burn More Calories?

Unlike physical exercise, mental workouts probably do not demand significantly more energy than usual. Believing we have drained our brains, however, may be enough to induce weariness

By Ferris Jabr

Between October and June they shuffle out of auditoriums, gymnasiums and classrooms, their eyes adjusting to the sunlight as their fingers fumble to awaken cell phones that have been silent for four consecutive hours. Some raise a hand to their foreheads, as though trying to rub away a headache. Others linger in front of the parking lot, unsure of what to do next. They are absolutely exhausted, but not because of any strenuous physical activity. Rather, these high school students have just taken the SAT. "I was fast asleep as soon as I got home," Ikra Ahmad told The Local, a New York Times blog, when she was interviewed for a story on "SAT hangover."

Temporary mental exhaustion is a genuine and common phenomenon, which, it is important to note, differs from chronic mental fatigue associated with regular sleep deprivation and some medical disorders. Everyday mental weariness makes sense, intuitively. Surely complex thought and intense concentration require more energy than routine mental processes. Just as vigorous exercise tires our bodies, intellectual exertion should drain the brain. What the latest science reveals, however, is that the popular notion of mental exhaustion is too simplistic. The brain continuously slurps up huge amounts of energy for an organ of its size, regardless of whether we are tackling integral calculus or clicking through the week's top 10 LOLcats. Although firing neurons summon extra blood, oxygen and glucose, any local increases in energy consumption are tiny compared with the brain's gluttonous baseline intake. So, in most cases, short periods of additional mental effort require a little more brainpower than usual, but not much more. Most laboratory experiments, however, have not subjected volunteers to several hours' worth of challenging mental acrobatics. And something must explain the feeling of mental exhaustion, even if its physiology differs from physical fatigue. Simply believing that our brains have expended a lot of effort might be enough to make us lethargic.

Brainpower
Although the average adult human brain weighs about 1.4 kilograms, only 2 percent of total body weight, it demands 20 percent of our resting metabolic rate (RMR)—the total amount of energy our bodies expend in one very lazy day of no activity. RMR varies from person to person depending on age, gender, size and health. If we assume an average resting metabolic rate of 1,300 calories, then the brain consumes 260 of those calories just to keep things in order. That's 10.8 calories every hour or 0.18 calories each minute. (For comparison's sake, see Harvard's table of calories burned during different activities). With a little math, we can convert that number into a measure of power:

—Resting metabolic rate: 1300 kilocalories, or kcal, the kind used in nutrition
—1,300 kcal over 24 hours = 54.16 kcal per hour = 15.04 gram calories per second
—15.04 gram calories/sec = 62.93 joules/sec = about 63 watts
—20 percent of 63 watts = 12.6 watts

So a typical adult human brain runs on around 12 watts—a fifth of the power required by a standard 60 watt lightbulb. Compared with most other organs, the brain is greedy; pitted against man-made electronics, it is astoundingly efficient. IBM's Watson, the supercomputer that defeated Jeopardy! champions, depends on ninety IBM Power 750 servers, each of which requires around one thousand watts.

Energy travels to the brain via blood vessels in the form of glucose, which is transported across the blood-brain barrier and used to produce adenosine triphosphate (ATP), the main currency of chemical energy within cells. Experiments with both animals and people have confirmed that when neurons in a particular brain region fire, local capillaries dilate to deliver more blood than usual, along with extra glucose and oxygen. This consistent response makes neuroimaging studies possible: functional magnetic resonance imaging (fMRI) depends on the unique magnetic properties of blood flowing to and from firing neurons. Research has also confirmed that once dilated blood vessels deliver extra glucose, brain cells lap it up.

Extending the logic of such findings, some scientists have proposed the following: if firing neurons require extra glucose, then especially challenging mental tasks should decrease glucose levels in the blood and, likewise, eating foods rich in sugars should improve performance on such tasks. Although quite a few studies have confirmed these predictions, the evidence as a whole is mixed and most of the changes in glucose levels range from the miniscule to the small. In a study at Northumbria University, for example, volunteers that completed a series of verbal and numerical tasks showed a larger drop in blood glucose than people who just pressed a key repeatedly. In the same study, a sugary drink improved performance on one of the tasks, but not the others. At Liverpool John Moores University volunteers performed two versions of the Stroop task, in which they had to identify the color of ink in which a word was printed, rather than reading the word itself: In one version, the words and colors matched—BLUE appeared in blue ink; in the tricky version, the word BLUE appeared in green or red ink. Volunteers who performed the more challenging task showed bigger dips in blood glucose, which the researchers interpreted as a direct cause of greater mental effort. Some studies have found that when people are not very good at a particular task, they exert more mental effort and use more glucose and that, likewise, the more skilled you are, the more efficient your brain is and the less glucose you need. Complicating matters, at least one study suggests the opposite—that more skillful brains recruit more energy.*

Not so simple sugars
Unsatisfying and contradictory findings from glucose studies underscore that energy consumption in the brain is not a simple matter of greater mental effort sapping more of the body's available energy. Claude Messier of the University of Ottawa has reviewed many such studies. He remains unconvinced that any one cognitive task measurably changes glucose levels in the brain or blood. "In theory, yes, a more difficult mental task requires more energy because there is more neural activity," he says, "but when people do one mental task you won't see a large increase of glucose consumption as a significant percentage of the overall rate. The base level is quite a lot of energy—even in slow-wave sleep with very little activity there is still a high baseline consumption of glucose." Most organs do not require so much energy for basic housekeeping. But the brain must actively maintain appropriate concentrations of charged particles across the membranes of billions of neurons, even when those cells are not firing. Because of this expensive and continuous maintenance, the brain usually has the energy it needs for a little extra work.

Authors of other review papers have reached similar conclusions. Robert Kurzban of the University of Pennsylvania points to studies showing that moderate exercise improves people's ability to focus. In one study, for example, children who walked for 20 minutes on a treadmill performed better on an academic achievement test than children who read quietly before the exam. If mental effort and ability were a simple matter of available glucose, then the children who exercised—and burnt up more energy—should have performed worse than their quiescent peers.

The influence of a mental task's difficulty on energy consumption "appears to be subtle and probably depends on individual variation in effort required, engagement and resources available, which might be related to variables such as age, personality and gluco-regulation," wrote Leigh Gibson of Roehampton University in a review on carbohydrates and mental function.

Both Gibson and Messier conclude that when someone has trouble regulating glucose properly—or has fasted for a long time—a sugary drink or food can improve their subsequent performance on certain kinds of memory tasks. But for most people, the body easily supplies what little extra glucose the brain needs for additional mental effort.

Body and mind
If challenging cognitive tasks consume only a little more fuel than usual, what explains the feeling of mental exhaustion following the SAT or a similarly grueling mental marathon? One answer is that maintaining unbroken focus or navigating demanding intellectual territory for several hours really does burn enough energy to leave one feeling drained, but that researchers have not confirmed this because they have simply not been tough enough on their volunteers. In most experiments, participants perform a single task of moderate difficulty, rarely for more than an hour or two. "Maybe if we push them harder, and get people to do things they are not good at, we would see clearer results," Messier suggests.

Equally important to the duration of mental exertion is one's attitude toward it. Watching a thrilling biopic with a complex narrative excites many different brain regions for a good two hours, yet people typically do not shamble out of the theater complaining of mental fatigue. Some people regularly curl up with densely written novels that others might throw across the room in frustration. Completing a complex crossword or sudoku puzzle on a Sunday morning does not usually ruin one's ability to focus for the rest of the day—in fact, some claim it sharpens their mental state. In short, people routinely enjoy intellectually invigorating activities without suffering mental exhaustion.

Such fatigue seems much more likely to follow sustained mental effort that we do not seek for pleasure—such as the obligatory SAT—especially when we expect that the ordeal will drain our brains. If we think an exam or puzzle will be difficult, it often will be. Studies have shown that something similar happens when people exercise and play sports: a large component of physical exhaustion is in our heads. In related research, volunteers that cycled on an exercise bike following a 90-minute computerized test of sustained attention quit pedaling from exhaustion sooner than participants that watched emotionally neutral documentaries before exercising. Even if the attention test did not consume significantly more energy than watching movies, the volunteers reported feeling less energetic. That feeling was powerful enough to limit their physical performance.

In the specific case of the SAT, something beyond pure mental effort likely contributes to post-exam stupor: stress. After all, the brain does not function in a vacuum. Other organs burn up energy, too. Taking an exam that partially determines where one will spend the next four years is nerve-racking enough to send stress hormones swimming through the blood stream, induce sweating, quicken heart rates and encourage fidgeting and contorted body postures. The SAT and similar trials are not just mentally taxing—they are physically exhausting, too.

A small but revealing study suggests that even mildly stressful intellectual challenges change our emotional states and behaviors, even if they do not profoundly alter brain metabolism. Fourteen female Canadian college students either sat around, summarized a passage of text or completed a series of computerized attention and memory tests for 45 minutes before feasting on a buffet lunch. Students who exercised their brains helped themselves to around 200 more calories than students who relaxed. Their blood glucose levels also fluctuated more than those of students who just sat there, but not in any consistent way. Levels of the stress hormone cortisol, however, were significantly higher in students whose brains were busy, as were their heart rates, blood pressure and self-reported anxiety. In all likelihood, these students did not eat more because their haggard brains desperately needed more fuel; rather, they were stress eating.

Messier has related explanation for everyday mental weariness: "My general hypothesis is that the brain is a lazy bum," he says. "The brain has a hard time staying focused on just one thing for too long. It's possible that sustained concentration creates some changes in the brain that promote avoidance of that state. It could be like a timer that says, 'Okay you're done now.' Maybe the brain just doesn't like to work so hard for so long."

*Editor's note: The last two sentences of the seventh paragraph were edited after publication for clarity and accuracy

7 FITNESS MYTHS YOU SHOULD STOP BELIEVING

BY FIORA STEVENS

Myth #1: Crunches and Ab Exercises Help Bust Belly Fat

Truth: While exercises that target the abdomen can help tone and strengthen the muscles near your belly, they won’t make that paunch go away on their own. The human body doesn’t get rid of fat just in certain areas; when you exercise, fat loss is a full-body phenomenon. To minimize belly fat, focus on intense cardio workouts, supplemented by a weight lifting regimen (which should, of course, include core exercises like crunches). And most importantly, fix your nutrition!

Myth #2: Women Should Stick to Light Weights to Avoid Bulking Up

Truth: The vast majority of women simply don’t have enough testosterone in their bodies to build the Arnold-like muscle mass that some want to avoid. In fact, lifting heavy weights will instead help women lose weight, gain increased definition, and build confidence.

Myth #3: Sweat is a Good Indicator of How Hard You’re Working

Truth: While a sweat-soaked t-shirt might make you feel super satisfied after a tough workout, there’s really no relationship between how much you sweat and how hard you’re working. So next time you’re at the gym? Consider leaving that 90s style sweat suit at home.

Myth #4 : No pain, No Gain

Truth: There’s a big difference between pain and discomfort, says Michael Lagomarsine, an expert based out of Boston University’s Athletic Enhancement Center.

While you may have some minor muscle soreness after a particularly hard workout, anything that actively hurts while you’re doing it could be causing you damage. Extreme muscle pain for more than a day or two after a workout likely indicates injury or overtraining.

Myth #5: Stretching Before a Workout Helps Prevent Injuries

Truth: Multiple studies have found that stretching before a workout actually does nothing to prevent injuries. In fact, those who stretch before a run actually tend to wind up with more injuries than those who don’t.

Stretching after exercising seems to be the best option for those who want to avoid delayed onset muscle soreness. Instead of using stretches before a workout, try to warm-up with some simple jogging, jumping jacks or anything that’ll warm-up the muscles you’ll be using for your workout.

Myth #6: Low Intensity Cardio Burns Fat Best

Truth: You’re probably familiar with the “fat burn” zone on your favorite piece of cardio equipment, but there’s really no backing for the idea that lower intensity cardio is better than high intensity cardio when it comes to losing weight.

According to exercise specialist and fitness author Tom Holland, fat loss is all about burning calories, and the more intense your workout, the more calories you’ll burn.

Myth #7: Weight Machines Are Safer Than Free Weights.

Truth: This myth may actually put you at a higher risk for injury. Many gym enthusiasts stick to weight machines rather than learning how to use free weights, because they believe that the machine will correct their form and ensure that they don’t hurt themselves.

But there are still tons of ways you can use a weight machine that can damage your muscles and joints, from height and length adjustment to using weights that are too heavy to using the wrong muscle groups to push or pull. Whether you choose to use free weights or weight machines, make sure you have a qualified trainer show you the ropes before you get started.

Sources:

• http://www.webmd.com/fitness-exercise/features/top-9-fitness-myths-busted
• http://www.webmd.com/fitness-exercise/features/strength-training-for-women
• http://www.boston.com/lifestyle/2013/02/08/fitness-myths-debunked/vhIwKKnj82eeXRIs3bCRaI/story.html?pg=9
• http://www.huffingtonpost.com/2012/05/09/health-fitness-myths_n_1504449.html

Why Are Thin People Not Fat?

Why Are Thin People Not Fat?

You probably know at least a couple of people who just don't seem to get fat no matter how much they eat. Some of them don't even do much exercise. But is it really true that some of us gain weight more easily than others, or do thin people just eat less calories?

Most of the studies on obesity and weight loss have been done on subjects who are overweight to begin with. A BBC Horizon documentary titled Why are thin people not fat? looked at the obesity problem from a different angle. They chose subjects who were naturally thin and stuffed them with excess calories. None of the participants had watched their food intake before, but their weight had remained roughly the same for years.

The subjects were told to eat at least double their usual calories and to avoid exercise for four weeks. The target energy intake for men was 5,000 kcal and somewhat less for women. The purpose was to find out whether naturally thin people would start gaining weight, given a sufficiently large amount of calories. It was no exercise in healthy eating either: the menu included processed, calorie-dense foods such as cakes and milkshakes. Precisely the kind of thing that should make one fat.

The documentary begins by mentioning a similar experiment done on Vermont prison inmates in 1967. The inmates were grossly overfed with the purpose of studying the hormonal changes that happen when a person becomes obese. The prisoners who signed up were promised an earlier release.

Each inmate was supposed to increase their body weight by 25 percent. However, as the experiment progressed, it turned out that no matter how high the energy intake got, some of the inmates could not reach their targets. Despite eating and eating, they just didn't gain enough weight. One of them could not increase his body weight more than 18%, even though his daily calorie intake reached a whopping 10,000 kcal. 

For years, experts argued over the results of the Vermont prison study. According to the classical model of calories in, calories out, such high intakes should have led to a dramatic weight gain, especially since exercise was forbidden during the experiment. So how did some of the inmates stay thin?

This is the question that the BBC experiment tries to answer. I recommend watching the whole documentary, but here's a summary of the results:

• All participants had trouble reaching their energy intake goals
• Energy-dense foods such as chocolate made reaching the goals easier
• Some of the subjects gained more weight than others
• One of the subjects gained almost no weight but increased his muscle mass
• All subjects returned to their normal weights after the experiment

These results confirm the observations from the Vermont prison study: despite very high calorie intakes, some people have a harder time gaining weight than others. The documentary also explains how naturally thin people are able to stay thin:

• Appetite has a genetic basis
• Age, weight, and diet of the mother during pregancy influence the child's weight
• Eating habits learned during childhood carry on until adulthood
• Naturally thin people avoid excess calories instinctively
• People have a certain "natural weight" towards which the body aims
• Basal metabolic rate plays a strong role in energy expenditure
• The feeling of hunger is related to the number of fat cells
• The number of fat cells can grow but never diminish

There's a lot of debate these days over the importance of basal metabolic rate (BMR) in the calories in, calories out model. It's interesting to note that nobody eats the exact same amount of calories per day, and yet weight remains in a very narrow range (at least in healthy, thin subjects). The one subject who stuck to his 5,000 kcal intake but gained almost no weight supports the idea that there is a kind of setpoint that the body tries to maintain regardless of calorie intake.

It also looks like in some people, the mechanisms to preserve the natural weight setpoint are stronger than in others. Increased heat production is obviously one way to maintain weight during increased energy intake. Some people (Michal Eades comes to mind) have also argued that as the number of calories eaten increases, the body starts to burn them by increasing small, almost involuntary movements such as tapping your fingers, moving your legs, etc. – physical activity which is not considered exercise but still uses up extra energy. I think this theory makes sense.

The last two points of the list are especially interesting. There are two key attributes to fat tissue: the size and number of fat cells. The number of fat cells in your body is typically pretty much determined during adolescence. Thus, eating affects first and foremost the size of your fat cells. As you store and burn energy, the fat cells in your body grow and shrink accordingly.

That's not all there is to it, however. If you keep eating even after the fat cells have grown to their maximum size, at some point the body will begin to produce new fat cells to store all that extra energy. The tendency to produce more fat cells probably depends on the individual.

The problem is that according to our current understanding, the number of fat cells can only be increased, never decreased. This means that any new fat cells produced as a result of (prolonged) overeating will always stay with you. What's worse, as the purpose of fat cells is precisely to store energy, the body will now send more signals of hunger to your brain to keep those fat cells filled up. Obviously this makes following diets that rely only on cutting back on calories very difficult.

The overall message of the documentary is that being naturally thin is a combination of many factors, some of which are genetically determined and some a result of the environment. Of course, individual choice also plays a role, but the studies on small children given unlimited candy show that even before we have the capability to think rationally about our food choices (kids will eat as much candy as they desire), there are differences among people.

For those who have to struggle to maintain or lose weight, things are more difficult – though not impossible by any means. It just means paying attention to your diet, venturing beyond governmental recommendations, and trying on yourself what works. I've had many overweight people tell me how difficult it is to lose weight, and then when I ask them if they've tried for example a basic low-carb diet, they've either tried it for a few weeks and quit, or they've deemed it "unhealthy", because all they can picture is Atkins on his deathbed and slices of bacon clogging their arteries.

Five appetite control foods that suppress cravings without adding calories

Five appetite control foods that suppress cravings without adding calories
by Mike Adams

There is a reality about weight loss that people need to be aware of. Losing weight requires you to feel hungry from time to time. There is no way to lose weight without feeling some degree of hunger. Believe me, I have exhaustively explored this issue. I have tried appetite suppressants. I have tried food combinations. I have tried meal-timing strategies. I have tried just about everything natural under the sun to eliminate those hunger pangs and food cravings that you get when you are attempting to lose weight and there is nothing that completely eliminates those cravings. Hoodia gordonii helps, as I've stated in previous articles, but it by no means turns off your hunger like a light switch.

There are many strategies that help reduce hunger: avoiding refined carbohydrates, getting plenty of natural sunlight on your skin, drinking large amounts of water on a regular basis, and getting plenty of fiber in your diet. But there is nothing that absolutely eliminates hunger. The bottom line is that if you are going to lose weight, you are going to experience hunger at one time or another. This is especially true if you, like me, engage in strength training. Nothing gets your appetite whipped into a fury like the leg press.

The key in all this is realizing there's nothing wrong with experiencing hunger from time to time. It's a normal human response to a decrease in your consumption of calories. The problem that most people encounter when they feel hungry is they feel it's some sort of emergency. It feels like they are dying or wasting away when, in fact, the body is just signaling that it doesn't have enough calories to add new fat to the fat stores it's already carrying around. The first feelings of hunger are really more of a false alarm than anything to be concerned about. At least from a logical point of view. (But when you feel like you're starving, logic goes out the window, right?)

A person who is aiming for a low percentage of body fat learns to manage their hunger so that it becomes something they can live with. In my own experience with losing weight -- and remember, I dropped 50 pounds of body fat using absolutely no drugs or pharmaceuticals of any kind -- I found that there are several "lifesaving" foods and beverages you can turn to when you are feeling intense hunger pains but you don't want to consume foods that add significant calories to your daily intake.

These foods and drinks are what I call emergency appetite control foods. What these foods and beverages have in common is that they make your stomach feel like it's full of calorie-rich foods. But in reality, you are filling your stomach with foods that contain almost no calories or carbohydrates. This way, even though your stomach is full, you are not adding calories to your intake. But your body is temporarily fooled into thinking you've just woofed down a triple-plate buffet.

In other words, if you eat two cups of cashews versus two cups of cabbage, your body can't really tell the difference for the first few minutes. Your stomach will turn off the hunger signals thinking you have eaten a large quantity of food regardless of whether you are eating cabbage or cashews, but in fact the cabbage may only contain 20 calories while the cashews contain as much as 900 or even 1000 calories. Two cups of cashews provides probably half the calories you need for the entire day, whereas two cups of cabbage provides virtually no calories whatsoever. You burn off the cabbage just digesting it. (Raw cabbage is, in fact, an outright cure for ulcers. But that's another article...)

Emergency appetite control food #1
Fresh drinking water. That's right: water is a powerful appetite suppressant and if you drink an 8-ounce glass of water when you first start feeling hungry, you will find that it suppresses your appetite in nearly every case. If you just drink a full glass of water and have the discipline to wait 10 minutes, you will find that your appetite is either completely gone or dramatically reduced.

Your next choice, if water does not do the trick for you, is to purchase a 32-ounce quart of natural, organic vegetable broth. You can get organic vegetable broth from Trader Joe's, health food stores, or even many of the finer grocery stores that have a natural health section. The key is to get organic vegetable broth that does not contain excitotoxins. These are ingredients that cause neurological disorders because they overexcite and harm nerve cells. Those ingredients are MSG, yeast extract, autolyzed yeast extract, hydrolyzed vegetable proteins, and other similar ingredients. Warning: watch out for broth products made by Kitchen Basics. They claim their products don't contain MSG or yeast extract, but when I tried their product, I experienced a massive "MSG headache" that tells me it contains free glutamic acid that isn't listed on the label. (I'm very sensitive to MSG.) The brand of broth I buy is Trade Joe's house brand, which does not contain free glutamic acid.

You can also choose organic chicken broth if you prefer the flavor of chicken. Once you have that, simply empty the entire quart into a very large bowl, heat it up and eat it like soup. You will probably be unable to get through the entire bowl without feeling full. And how many calories have you consumed? Not 900 like you get in two cups of cashews or 1200 like in a big Mac, not even 300 calories like you get from a typical protein bar, instead you get 20 calories only. That's right: you can feel full on 20 calories by drinking an entire quart of organic vegetable broth.

Emergency appetite control food #2
The next best strategy is to turn to green vegetables such as lettuce, cabbage, bokchoy, and other leafy vegetables. They have so few calories that in my own diet, I don't even count them. That's right: I allow myself to eat an unlimited quantity of any green leafy vegetables without even recording the number of calories I have consumed. In my book, they are "free" foods.

It takes just as many calories for your body to digest them as you get out of the foods themselves. And yet at the same time, they fill your stomach and make you feel full, turning off the hunger signals in your brain. You may have also heard these called "negative calorie foods."

You can consume these green leafy vegetables in a couple of ways. Most people don't like to eat them plain. Instead, you can fill up a very large bowl (I am talking about something the size of a family dinner salad bowl) with lettuce and salad greens, then add only 100 calories worth of salad dressing. You will want to find some of the lower calorie salad dressings out there, and of course you want to avoid MSG, high-fructose corn syrup, and other ingredients in salad dressings. There are many very good salad dressings that only have 25 calories per tablespoon. Using those dressings, you can put four tablespoons of salad dressing on your salad and start munching away. In a few minutes, you will feel quite full and yet will have only consumed 100 calories that count. Remember the calories for the green leafy vegetables are free. You only count the calories of the salad dressing itself. This is an excellent way to fill your stomach and turn off your hunger signals while only giving yourself 100 calories.

Another strategy that uses green leafy vegetables is to stir fry them in a pan with no oils whatsoever. Just use water and flavoring such as onions, garlic and soy sauce. Simply stir fry all the green vegetables you want, add the spices and eat it. I do not count the calories in onions or garlic either, nor do I count the calories in soy sauce since none of these spices have very high calorie density. As a result, that entire meal goes in your stomach and counts for zero calories. Once again, it's a great way to curb you appetite without consuming large quantities of calorie rich food.

Emergency appetite control food #3
This is one of my favorites: I call it my "instant banana pudding" recipe, but of course, it's nothing at all like store-bought pudding. You'll need a blender for this one.

Add a quart of soy milk to the blender, then a couple of scoops of unsweetened banana-flavored simply natural spirutein soy protein powder. Add stevia powder as the sweetener. I also toss in some supergreens powders, but you may want to avoid that at first, since it's an acquired taste (and it turns your banana pudding green).

If you were to blend this up, you'd have a banana-flavored soy protein shake. But we're not done yet: while the blender is running, put in about 1/2 tablespoon of guar gum powder, plus another 1/2 tablespoon of xanthan gum powder. These are thickeners. Within seconds, your blender will start whining and the whole mixture will attain the consistency of pudding. Now just pour it into a bowl and eat it like banana pudding! The mixture has near-zero carbs, no sugars, and is high in soy protein. Plus, it tastes great and fills you up fast. This is my favorite choice for a late-night appetite emergency.

You can get guar gum and xanthan gum at a health food store, or order online at a vitamin supplier.

Emergency appetite control food #4:
The last food is pickles. That's right, pickles. But I am not talking about the pickles you find at a regular grocery store. Nearly all pickles you find in grocery stores contain artificial food coloring. They have a yellowish tint to them that has been added through the use of chemical colors. This is not a natural ingredient and so it is something you want to avoid purchasing. Instead, you want to buy completely natural pickles like the ones you get at Trader Joe's that are made without artificial colors or flavors and that have an extremely low calorie count as well. An entire jar of pickles may give you only 50 calories or so and yet they can be quite satisfying and take up a considerable amount of space in your stomach, thereby turning off your appetite cravings.

Just don't buy pickles containing any added sugars or artificial colors. Some pickles are, believe it or not, loaded with sugar. They're more like candied cucumbers than pickles. Read the ingredients labels to be sure what you're getting.

By the way, while you're eating pickles, it's an excellent time to take some calcium and mineral supplements, too. The acidity of the pickles will accelerate the absorption of calcium.

Emergency appetite control food #5:
Here's an easy one: apples. Yep, apples. Eat the largest apple you can find. Sure, you'll get some calories and some carbs, but the apple will fill you up for quite a while, and that will stop you from eating far more calorie-dense foods.

Let me explain why this is such an effective strategy. If you're crazy hungry, it's very easy to reach for some processed foods (bag of chips, for example) and start munching away until you've consumed 1000 calories or more. And that's about half the total calories you need for the entire day!

But I dare you to try to eat 1000 calories worth of apples. It's impossible. You'll fill up even before reaching 400 calories, probably. Apples are great appetite suppressing foods because the bulky fiber fills up your stomach and turns off your appetite control hormones before you overeat. Plus, apples contain various phytonutrients, vitamins and minerals. They're even a decent source of folic acid.

How to further suppress your appetite:
One more supplementary strategy to all of this is that you can multiply the appetite suppressing effects of all foods by swallowing a couple of fiber tablets before you begin eating. Fiber tablets or capsules would include psyllium husk, glucomannan, oat bran fiber, apple pectin fiber, or other natural fibers. You can find fiber supplements at any health food store. Be careful to watch the dosage of the fiber and drink plenty of water as you take these pills because without adequate water, they can gum up in your digestive tract and in extreme cases, they can block your digestive tract. So, you want to drink plenty of water with them.

By consuming both the fiber and the water before you start eating, you've already significantly turned off your appetite. Then by consuming these extremely low caloric density foods and beverages, you will further suppress your appetite. You can get an entire meal into your stomach for 100 calories or less and you can trick your brain into thinking you consumed an all-you-can-eat buffet.

But there's a catch to all this: in about an hour or so, your body will figure out that there isn't much energy in the food you've consumed. Your hunger will begin to return, but at least you delayed the onset of that hunger by an hour or more. If you combine this with physical exercise, you can delay it even further because the very act of exercising releases stored body fat and converts it back into blood sugar, which raises your blood sugar level and suppresses your appetite cravings.

You can also extend the effect of this by taking appetite suppressant supplements. Hoodia gordonii is one I've reviewed quite extensively, and it is currently increasing in popularity. My own experience is that hoodia tincture can help, but even hoodia doesn't shut off appetite completely.

Also, you don't want to starve yourself by eating these 100-calorie meals all day long. Remember, starvation is the fastest way to train your body to hold on to body fat. These are just items to get you past a difficult time when your appetite is unbearably intense.

Each day, you still need to get nutrition into your body in the form of whole foods and whole food supplements. The kind of meals I consume are soups made with quinoa, salads with low-calorie dressing, raw fruits and nuts, or avocado shakes made by blending avocado with soy milk and stevia. Of course, I also consume my superfood shakes on a regular basis. They are made from superfoods green powders such as Berry Green or The Ultimate Meal.




Overall, keep in mind that weight loss takes effort. You will experience moments of intense hunger, and these low-calorie, filling foods are one excellent way to get through a difficult time without packing on the pounds.

The Best Low-Carb Fruits (and the Worst)

This one’s not just for all you low-carbers! Here’s a quick guide to the best and worst fruits according to their sugar content and nutritional value. If you enjoy sweets and find yourself relying (or perhaps suffering) on Splenda and mockalate far too often, enjoy a sensible selection of fruit instead.

Berries
Blueberries, strawberries, raspberries, blackberries, huckleberries, salmon berries, gooseberries – they’re all packed with antioxidants and vitamins. These little fiber bombs are the smartest, most nutritionally-dense fruit you can eat. Aim for a half-cup to one cup daily. Keep in mind that these fruits, especially strawberries and raspberries, are excellent on grilled meats and in salads, so go ahead and experiment! (Glycemic Index: generally low to mid-20′s)


Cherries
Cherries are similar to berries in terms of their antioxidant value. They have a bit higher natural sugar content, but they’re still very low-carb and are an excellent source of important fiber. Cherries are amazing with bacon, feta and greens; or try them smothered atop pork chops. Hungry yet? (GI: 22)


Apples and Pears
These northern fruits are related to the rose. They’re low in sugar and contain a respectable amount of fiber. While antioxidants aren’t exactly overflowing from your average Granny Smith, apples (and pears) are still a great way to satisfy a craving for sweetness without terrorizing your pancreas. (GI: 38


Grapefruits
Most citrus fruits are quite high in sugar, but grapefruits are not. In fact, their effect on blood sugar is less than apples and pears at only 25. Just don’t ruin a smart thing with a sprinkling of sugar on top! Grapefruit is excellent in salads, especially when paired with avocado slices.


Apricots and Peaches
With similar nutritional value as apples and pears, these stone fruits are a smart way to get a good dose of vitamin C and fiber. Avoid nectarines, which are much higher in sugar and are more akin to mangoes and papayas. (GI: 30s)


Figs

Oh, the forgotten fig. It seems to get lumped into the dates ‘n raisins category, but figs are just as low in sugar as strawberries, and are packed with fiber (all those tender, tiny seeds). Enjoy these fresh whenever they’re in season.

These fruits are high in sugar, so don’t make them a daily habit:

- Melons

Some low-carb guides will recommend melons, but you do have to be mindful of which ones you’re going for. Both cantaloupes and watermelons are very high in sugar (GI: 65, 100 respectively). We recommend making melons a rare treat.

- Mangoes and Papayas

Though not as sugary as pineapples, these fruits are best enjoyed infrequently. A better choice is the banana, which – although starchy and a 55 on the glycemic index – is a smarter energy source.

- Pineapples

Pineapple is the best source of bromelain, an enzyme that can help with joint health and inflammation. Some folks are intolerant or allergic (if you get irritated lip or mouth tissues after eating pineapple, this is why). Pineapple is very high in sugar, but it’s full of valuable nutrients in addition to bromelain, so enjoy it guilt-free from time to time.

Sources:

World’s Healthiest Foods

About: low-sugar fruits

How Much Body Fat Do We Need?
by Dr Andrew Weil MD

How low is too low for body fat percentage in women? I'm a kickboxer and karate student and have gone from 25% to 15% body fat in 8 months. I'm 25 years old.

We carry two kinds of fat in our bodies, essential fat which is stored in small amounts in bone marrow, organs, the central nervous system and muscles, and is needed for the normal, healthy functioning of all these body systems, and "storage" fat, which is stocked for energy. For men, essential body fat makes up about three percent of total body weight. For women, the percentage is higher - about 12 percent - because it includes amounts in the breasts, pelvis, hips and thighs believed necessary for normal female reproductive function.

For a woman of 25, a healthy range of body fat would be between 21-32 percent. This can increase slightly with age, to 23-33 percent for women between 40 and 59 and to 24 - 35 percent for those over 60. The healthy ranges in men are from 8-19 percent for those between the ages of 18-39, from 11-21 percent for those aged 40 to 59 and 13-24 percent for those over 60.

We now believe that, for women, the minimum body fat percentage should be between 13 and 17 percent although there's no hard and fast "rule" on what is too low for an individual. Keep in mind that there are several ways to measure body fat, and some are notoriously inaccurate, so the ranges and absolute numbers may vary. You may be able to tell when your body fat is too low by whether or not you're menstruating regularly. If your periods stop, nature may be telling you that you don't have enough body fat to nurture a fetus should you become pregnant. By turning off your menstrual cycle, your body is telling you that you are (temporarily) infertile. Please don't think of this as a convenient method of birth control - it isn't. You need normal hormonal function for more than just menstruation and fertility. For example, the health of your bones also depends on circulating levels of estrogen, the principal reproductive hormone in women.

Fitness expert, Dan Bornstein, tells me that when body fat percentage gets too low, energy levels and exercise performance decline. So does tolerance for cold. However, in general, as long as you continue to menstruate and as long as your energy level remains intact, your body fat percentage is probably OK. I would encourage you to gain a few pounds if your periods stop or become irregular or if you lack your usual energy.