Have you ever been in an exercise class where the instructor says something along the lines of asking you to put in a bit more effort and then you will have earned the extra sweet treat, or drink, or takeaway you’re going to have at the end? Or at the weekend coming, or just gone? Is there a simple link between food intake, exercise and weight loss as they implied?
It’s a tempting idea. If we just make a bit of extra effort and burn a few more calories we can have a guilt-free treat in the knowledge that we won’t suffer any ill effects. Some people find it motivational and it seems to make sense.
It’s also what a whole industry has been based on: the idea that if you increase the calories you burn you can increase the calories you take in (by a little less) and lose weight. All that’s needed is a little willpower that will soon be rewarded, in the form of a treat, and a simple calculation.
The problem is that this is not how your body works. You can’t just do a bit more and then take in a few more calories and expect to see good results. This thinking is flawed and will lead you astray if you follow it while trying to lose weight.
What is the Role of Exercise in Weight Loss
The problem is obvious from the widely seen outcome taking up exercise has a very modest effect on weight loss, much less than the arithmetic of calorie counting would lead you to expect.
The health benefits of exercise are real and I have discussed them in other articles on this site. It reduces the risk of Type 2 diabetes, stroke, and heart attack. A number of studies have also shown that people who exercise score higher on cognitive ability tests and are at a lower risk of developing cognitive impairment and dementia.
Also while exercise might not help greatly in losing weight it will help you to maintain your weight after you’ve lost it. That is, provided you control your calorie intake. However, a consistent increase in physical activity is required.
But, it is not going too far to state that exercise alone is of little use for weight loss. but extensive and repeated reviews of exercise intervention studies find that weight loss is less than expected.
Typically, people in research studies lose only a few pounds by increasing the amount of exercise where their diets were kept constant. In general, the amount of energy that study participants use in undertaking exercises has no correlation with their weight loss, if any.
So, exercise does your body and mind good, but it is not great for losing weight. Why is this?
Be Wary of Simplistic Calorie Counting
The idea that you can think in simple “calories in, calories out” terms can be traced to a publication from 60 years ago that outlined a simple rule to predict weight loss. It argued that a pound of human fat represents about 3,500 calories. Therefore, if you adjust your calorie burn or intake so that burn exceeds intake by about 500 calories per day you will lose about a pound of weight per week. On the other hand, if your intake exceeds your calorie usage by 500 calories a day you will gain about the same about the same.
But this is far too simplistic an analysis of the way in which the body responds to changes in calorie intake and burn.
The way in which the body acts is part of a much more dynamic system that will adjust to a change in one component of that system. So, for example, if you cut the number of calories you take in and/or do more exercise than usual you set off a number of changes in the body that affect how many calories you actually use.
As a result, you cannot predict changes in your body’s weight from these few pieces of data alone on the assumption that nothing else changes.
There is No Simple Relationship between Movement and Calorie Burn
Imagine a group of hunter-gatherers living in a remote area. They are moving most of the time looking for food. Now imagine your typical westerner: watching television, taking a bit of exercise (or not), working in a non-manual job, and eating what has been bought in the shop.
There is a far greater chance that the westerner will be over-weight. After all, their sedentary lifestyle means they are using far fewer calories than the hunter-gatherer. Lack of activity is then put forward as an explanation for the increase in obesity in western developed countries.
So goes the conventional wisdom. Except the evidence does not back up this story.
Anthropologists have studied the behaviour, activities and health of groups of hunter gathers. The standout finding is that the body energy they use in their daily lives is no higher that might be expected for the average person in the developed world.
The hunter-gatherers were certainly physically active and lean. But they burned the same amount of calories each day as the average American or European, after allowing for body size.
This raises the obvious question: how could it be that people who hunt and forage throughout the day for their food burn the same amount of energy as much more sedentary Westerners?
Exercise is only a Small Part of Daily Calorie Usage
A large part of the explanation is that it’s not only movement that burns calories. The number of calories we burn includes all the energy we need to run thousands of bodily functions that keep us alive.
There are three main components to energy expenditure: the basal metabolic rate (the energy used for basic functioning when the body is at rest; the energy used to break down food; and the energy used in physical activity.
Your basal metabolic rate does not depend on the exercise you take and we have little control over it. But it accounts for the largest part of energy usage, perhaps 60 to 80 percent of the total.
Digesting food accounts for about 10 percent. That leaves only 10 to 30 percent for physical activity, of which exercise is only a subset.
A second part of the explanation is likely that people such as hunter gatherers who know there will be large daily requirements to move to find food have developed societal structures that allow them to conserve energy by not moving much when not engaged in this primary activity. Westerners have no such need.
But if the hunter-gatherers are not using any more calories in a typical day, why are they so much less likely to be overweight? The answer is simple and needs very little research: their food is scarce and difficult to find so they don’t overeat.
The effort that they would need to make to increase their food intake makes it not worthwhile to do so – once they have reached a basic level that’s sufficient to sustain them.
There’s a very important lesson here for the next time you think that you deserve a treat because you have worked out. What you take in has a far greater impact on your weight than what exercise you do.
Your basal metabolic rate doesn’t change much as you increase food intake. You use about 10 percent of the additional food in digesting the food. Are you really going to increase the amount you burn in exercise by moving more when that accounts for less than 30 percent of the total burn. It’s highly unlikely.
That’s not to say you should forget about exercise, whether you wish to lose weight or not. Far from it. But it does explain why people who have gained weight find it extremely difficult to lose it simply by exercising more. Without other changes, especially in diet, just exercising more to lose weight probably won’t work.
Exercise Doesn’t Use as Many Calories as You Might Think
Using a widely respected body weight planner it is possible to see why increased exercise is unlikely to lead to significant weight loss in the absence of other changes. The calculations show that a 200-pound man who takes up 60 minutes of medium-intensity running four days per week for a month would lose just five pounds.
That’s a pretty good increase in exercise for a moderately heavy man. But it leads to weight loss of just 2.5% of the starting weight. Not nothing, but not a great return. But how likely is it that nothing else will change?
Will he be likely to have a treat (because he has earned it)? After all, increased exercise can make you feel hungry. It’s very possible that he could end up consuming more calories than he burned. People often overestimate how much energy they have burned during exercise and then eat more when they know they have worked out.
It’s likely also that our man will relax in other areas of his life in order to recover from this increase in activity. Or simply because the effort has actually made him feel tired. And he won’t feel guilty from having a well-earned break.
In either of these cases the weight loss will certainly be less.
Now take a person who is considerably overweight. They may need to lose much more weight than five pounds to have a meaningful impact on their lives.
How much time is this likely to take? Will they have the will power and the time in their lives to make this huge effort?
Probably not. So we usually do not see much weight loss with increased exercise although it can help to maintain a lower weight following weight loss.
Our Bodies Compensate for Extra Activity
Researchers have discovered a phenomenon called “metabolic compensation.” In plain language, your body changes based on the level of exercise you take. In effect, our bodies react to efforts to lose weight.
In a follow-up study of participants in TV’s The Biggest Loser, it was found that even though all the contestants had lost considerable weight during the show, they had mostly put the weight back on afterwards.
It wasn’t just that they went back to their old ways. More importantly, the study found that they had reduced their metabolic rate during the show, when they were deprived of adequate food and moved a lot, so that they were each burning up to 500 fewer calories each day. This is despite the increase in movement.
This is an obvious survival mechanism in reaction to food deprivation. But this effect persisted long after the show was over. It seems likely that some sort of body memory kicked in and adjusted to the possibility of future shortages, even though the deprivation was for a once off period only.
This has important implications: beyond some limit, you do not burn more calories by increasing your exercise level.
It may also be the case that our ability to burn calories may plateau at a certain daily level. The implication is that even if you increase the amount of exercise you do, you do not burn an increased number of calories. For most of us however, the chances are that we are not at that level.
So, we are more aware than ever of the increasing instances of overweight. We are more aware than ever of the benefits of exercise. There are more opportunities than ever to take exercise and more people are doing so. But average body weights keep rising.
Is There a Link Between Exercise and Weight Loss?
Exercise alone cannot address a weight problem. The attention needs to be placed on diet, on calorie intake. Simple ‘calorie in-calorie out’ calculations are meaningless. Avoid any thoughts that you’ve earned a treat if you exercise, if weight loss is your goal.
Diet control is central to weight loss. And it not just calorie counting. The form of the food you eat is also important.
Exercise has many health benefits. But weight loss should not be placed as a primary one. And be very wary of thoughts that you can eat junk foods and then burn it off.
The National Weight Control Registry studied the traits, habits, and behaviours of more than 10,000 people who have lost at least 30 pounds and kept it off for a minimum of one year.
The results showed that there are a number of commonalities among people who have lost weight successfully.
- They weigh themselves at least once a week.
- They restrict their calorie intake, stay away from high-fat foods, and watch their portion sizes.
- They exercise regularly, but do so in addition to calorie control and other beneficial lifestyle behaviours.
You need to control your diet and exercise. But here’s the important lesson: do not to count the calories burned in physical activity as meaning you can engage in extra eating if you are trying to lose weight.
It’s far better to pretend you are not exercising at all. Think of the health benefits you get from exercise. These are a good enough reason to exercise, not any possible weight loss benefits.