The quick takeaway
- The simplest equation relating energy use and food intake is that change in body size equals energy consumed minus energy expended on activity. This means that if you eat the same and exercise more you will lose weight. In reality it is not as simple as that.
- Recently a variation on this simple energy balance equation has been receiving a lot of publicity. According to the compensation energy balance model, as the energy requirements for physical activity increase, the amount of energy spent on basic metabolism decreases. This means that despite exercising more the total energy expenditure stays the same, so if you eat the same and exercise more, you will stay the same weight.
- The evidence suggests that what actually happens is somewhere between the predictions from these two models.
- There is evidence from studies of total energy expenditure for a degree of compensation, but not 100% compensation. Individuals with more body fat compensate more than lean individuals implying that it will be harder for those with significant body fat to lose weight with exercise.
- There is a considerable body of evidence which shows that undertaking exercise leads to weight loss although the weight loss achieved is less than anticipated from a simple application of the energy balance model.
- Increasing physical activity can lead to weight loss without dietary changes especially with high-intensity exercise maintained for long periods of time.
- A combination of high intensity aerobic exercise and resistance training is the best regime to reduce BMI and body fat.
- The combination of a calorie restricted diet and physical activity is superior for weight loss than either diet or physical activity alone.
- Most studies in this field measure body weight or BMI, but these may not be the best measures of the benefits of physical activity on body size.
- Adiposity may be reduced without weight loss as lean body mass is increased through physical activity, particularly resistance training.
- There may be other compensatory effects at play other than a decrease in certain metabolic activities. Some exercisers increase the amount of food eaten before or after activity, negating the potential weight loss benefits of the physical activity. Individuals undertaking exercise as part of a weight loss programme may reduce the amount of physical activity taken outside the programme such that their overall increase in physical activity is less than would be anticipated from participation in the exercise programme.
- There is some evidence that participating in physical activity supports other healthy lifestyle changes.
The full deal
For those people familiar with the energy balance equation, simply stated as change in body size will equal the energy consumed from food minus the energy expended in activity, it seems obvious that exercise will influence body weight. If people consume the same number of calories and exercise more, they will loose weight. If they consume the same number of calories and exercise less, they will put on weight.
In practice it does not always appear to work like this with some researchers pointing to the benefits of exercise in weight management and others maintaining that it does not play a role at all. The latter view is the most controversial so let’s start by looking at where it comes from and whether it is supported by the evidence.
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