In the last five posts I have looked into the relationship between exercise and weight loss, and found that although regular physical activity is associated with several improvements in health, its role in weight management is not so clear cut. In this final piece I’ll summarize the information and results from the previous posts, and also discuss some of the limitations with most of the studies looking into the link between exercise and weight loss. Last, but no least, I’ll draw some conclusions.
Exercise hasn’t always been advocated for weight loss (Post 1)
Prior to the 1950s there were few health practitioners who believed that exercise was effective for someone who wanted to lose weight. Studies done by the French-American nutritionist Jean Mayer showed a connection between a sedentary lifestyle and higher body mass index.
Physical activity can promote weight loss through several different mechanisms (Post 2)
Increased energy expenditure during exercise, excess post-exercise oxygen consumption and muscle growth are some of the factors resulting in an increased basal metabolic rate and elevated energy expenditure both during and after exercise (3,4,5,6,7).
It’s difficult to estimate the varying importance of the mentioned factors in regards to weight management, but it’s clear that energy expenditure during exercise isn’t the only factor involved.
Compensatory mechanisms could explain differences in exercise-induced weight loss (Post 3)
Physical activity seems to only result in partial energy compensation from food. However, individual’s respond differently, and while some people increase their energy intake following exercise, others actually seem to eat less. Studies also show that some individuals who exercise end up compensating for the increased energy expenditure by being less active throughout the rest of the day. Both physiological, neural and psychological factors seem to influence compensatory mechanisms, but more research is needed to establish why and how people react differently to exercise (17,18,19,20,21).
The amount of exercise performed seems to also influence compensatory mechanisms, and one newer study shows that a “moderate dose of exercise induced a markedly greater than expected negative energy balance, while a higher dose induced a small but quantifiable degree of compensation” (22).
Some people gain weight from exercise (Post 4)
Heavy resistance training promotes muscle growth, and if body fat remains unchanged or increases, sticking to a heavy resistance training program will result in weight gain.
Some people also gain weight when they follow a training program based on aerobic exercise (18).
Compensatory mechanisms and other factors (e.g., inflammation, microbiota, intestinal permeability) could explain these differences in exercise-induced weight loss. Prolonged, high-intensity exercise potentially disrupts gut barrier function (23,24) and therefore could “initiate” a vicious cycle of inflammation, leptin resistance, insulin resistance and weight gain.
Exercise on it’s own is not very effective for losing weight (Post 5)
Using both diet and exercise seems to be the most effective approach for individuals who want to lose weight. However, the additional weight loss from a combined approach is only marginal compared to diet alone. Isolated aerobic or anaerobic exercise without dietary intervention only cause a modest weight reduction. People respond differently to exercise and while some individuals lose a lot of weight by engaging in some type of regular physical activity, others maintain or gain weight (18,25,26,27).
Some studies show that high-intensity intermittent exercise results in greater weight loss than standard aerobic exercise (28,29).
Aerobic exercise seems to promote slightly better fat loss compared to resistance training, but it’s difficult to accurately measure the two (28,29).
Health practitioners at each end of the spectrum either claim that exercise is useless for someone who want to lose weight or that exercise is great for weight loss. Studies show that they might both be right; some people respond to exercise with a substantial weight reduction while others respond poorly (18). This discrepancy is probably caused by a combination of compensatory mechanisms and physiological differences.
Several issues arise when the benefits of physical activity are measured over several months in human subjects. While it’s possible to give specific lifestyle instructions it’s still difficult to control additional activity during the day, compensatory mechanisms, sleep etc. Many of the studies investigating the relationship between physical activity and weight loss also have methodological shortcomings that could impact the results.
Epidemiological studies linking sedentary lifestyle and obesity have made exercise synonymous with a lean physique (1,2). However, studies show that although regular aerobic and anaerobic exercise could improve several markers of health, they only seem to induce modest weight loss in most people (18,25,26,27).
The actual energy expenditure during a regular workout is quite low compared to what is achievable through diet, and some individuals seem to compensate for the increased energy expenditure by eating more food (17,18,19,20,21).
Weight loss plans should focus on diet, and exercise prescription should be based on individual responses to physical activity.
All posts in this series on exercise and weight loss
Part 1: Introduction and history
Part 2: How does physical activity affect bodyweight?
Part 3: Physical activity, increased appetite and food intake
Part 4: Exercise and weight gain
Part 5: How much do I lose?
Part 6: Summary, discussion and conclusions