We all know exercise helps you lose weight. Right? So why do some of us fail to shed centimetres even though we do plenty of exercise?
Jeff and Liz are like many couples in their early 40s – they love good food, drink a little too much wine and don't do enough exercise.
Unfortunately their lifestyle started taking its toll on their waistlines. So last year they decided to do something about it together and embarked on a new regime of healthy eating, drinking less, and exercising regularly.
Three months later Jeff had lost four kilos, whereas Liz's weight was the same. It's an all too familiar story yet it's one we don't really know the answer to.
Why is it that some people can slog their hearts out at the gym several days a week to discover their scales are telling them the same story?
Weight loss through exercise works 'in theory'
Exercise can be an effective way to lose weight, says Dr Nathan Johnson, an exercise physiologist based at the University of Sydney.
This has been illustrated by plenty of scientific studies that placed people on exercise programs and calculated, based on the energy cost of the exercise, how much weight they should lose. More often than not, study participants lost weight as predicted.
"On the whole people do lose weight when they stick to an exercise plan and nothing else changes," says Johnson.
However, in the real world what tends to happen is people who exercise either don't lose weight, or lose a small amount that they then put back on over time.
A study by an US group of researchers is a good illustration of what typically happens with exercise, says Johnson.
Previously sedentary overweight and obese postmenopausal women were put into either a non-exercise control group or one of three exercise groups with an exercise energy expenditure of 4, 8, or 12 kcal/kg/week (KKW).
At the end of the six-month study the researchers observed no difference in actual and predicted weight loss between the 4 and 8 KKW exercise groups. The 12 KKW group, who exercised for 194 minutes a week, produced only about half of the predicted weight loss.
"People tend to go well for a few weeks and lose the amount of weight you'd expect but then things tend to go the wrong way after that…they begin to not lose as much weight as you'd expect in the end," says Johnson.
"The authors speculate that people are behaviourally compensating by either changing their diet or their physical activity."
Cancelling out your hard work
Johnson says many of us are either consciously or subconsciously 'self-sabotaging' in some way.
For instance, you may be less physically active overall throughout your day because you are exercising. This means you're unwittingly cancelling out the benefits of the exercise you've been doing.
"If I start a regular exercise program I may find myself sitting down more or taking the less active option [in other activities]," says Johnson.
"The other thing is people may change their dietary behaviour whether that means eating more, or eating more energy dense foods."
Most of us can identify with this feeling of having 'earned' a treat after a big work out session.
"The actual medicine itself, if we think of exercise as a medicine actually works, …but it's the implementation of it that tends to fall short," he says.
Diet damage is hard to undo
The other issue is that people can do a lot of harm through their diet that is almost impossible to make up through exercise, says Johnson.
"Making a bad eating decision can require a lot of exercise to expend the equivalent amount of energy," he says.
For example, you need to do about 45 to 60 minutes of exercise to offset the kilojoules contained in a burger from a popular fast food joint.
"When you combine the typical choices people make throughout the day, like a snack in the morning, a burger for lunch, we often find that we just can't undo the bad work that's been done."
And the truth is, most of us are largely unaware of how much energy is in the food that we're putting into our bodies, particularly when it comes to sugary or fatty foods.
Putting calories into context
Researchers from Texas found that when they gave people menus that illustrated how much exercise was needed to burn off the calories for each item of food, they opted for healthier choices.
The study of 300 men and women aged 30 and under were divided into three groups. One group received a regular menu, the second group received the same menu with the calorie content for each item, and the third group had a menu that listed calories as well as how many minutes of brisk walking it would take to burn those calories.
The third group ordered and consumed fewer calories compared to the other groups.
The findings showed that putting calories into context might go some way to changing the eating habits of adults, the study authors said.
Right type of exercise
Sometimes there's also a big difference between what people think is exercise, and what exercise actually is, says Johnson.
"People misunderstand what we talk about as exercise and think that just getting up from their chair or having a stroll is adequate."
"There's a perception that they've done some exercise so that offsets all ills."
He says many of us will take the easy route when it comes to exercise.
"Adults inherently tend to select the lazier option of things and this tends to come as self-supporting advice."
"If you stick to that then you're suddenly not doing the recommended regular amount of exercise to keep that energy input energy output balance in check."
Fat burning exercise
When we move our bodies we need energy to be used up at a higher rate to burn fat. The key is to expend as much energy as you can, says Johnson.
He recommends aerobic type activity involving the use of large muscles if you want to lose weight. This is because the more muscles you use, the more energy you need to use to support the activity.
This can include activities like brisk walking, running, cycling, kayaking, swimming as well as many team sports.
It's best to try and accumulate activity for prolonged periods of at least 30 minutes but the more the better, advises Johnson.
Some people respond better
It's also true that some people respond to exercise better than others, but it depends on what outcome you are measuring, says Johnson. For instance, if we're talking about fitness, measured as aerobic capacity, part of that is genetically determined.
"We don't quite have a handle on which genes cause it, but there is definitely evidence that some people get more benefit in terms of fitness from exercise programmes than others".
However, when it comes to weight loss from exercise, having a genetically higher chance of being overweight or obese doesn't mean that you won't respond to exercise as well as anyone else does.
"While there is some evidence of a genetic component to being overweight or obese, the important thing is that there's absolutely no evidence that it changes how people respond to an exercise program."
Don't worry about the scales
According to Johnson, it's actually not weight per se that's the problem, it's fat and in particular, where it is stored.
Most rugby league or union players are overweight in terms of body mass index because they have a lot of muscle. Pear-shaped women typically store excess fat around their hips and bottoms. This is known not to be detrimental to their health, explains Johnson.
Instead it's the fat stored around the abdomen and organs that we should be worried about.
For example, fat stored in the liver, even in small amounts, can have significant consequences on health and the risk of disease, says Johnson.
But the great news is that exercise can reduce these fats, whether it's visceral fat that wraps around organs or whether it's fat in the organ itself – for instance fat in the liver, heart or pancreas.
"It appears these fats can actually be reduced or even got rid of in some of these organs even without losing weight and that's a really important message," he says.
"Don't worry about what's on the scales, worry about doing exercise because we know, aside from all of its benefits, it helps reduce fat from these areas".
Benefits beyond weight loss
It's also important to remember there are a host of benefits to exercise beyond weight loss, says Johnson.
Most people looking to lose weight are at high risk of diseases like heart disease and type 2 diabetes. Research shows that exercise can reduce these risks.
"People at risk of diabetes can halve their chances of the disease by doing moderate amounts of exercise," says Johnson.
Exercise has also been shown to help improve heart function and blood pressure.
The right type of exercise can also reduce depression and anxiety, improve bone health, and reduce risk of falls in old people, he adds.
"The message should move beyond weight loss and be more about actually doing sustainable exercise and doing it regularly for all these types of benefits."
"Otherwise people just end up in perpetual failure… of trying new diets and new fad exercise regimes."
"What we're really about is trying to encourage people to adopt healthy eating and physical activity as part of every day life."
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