This is why treadmills and exercise bikes display calories and many folks obsess about burning those “extra calories” (often only to eat or drink them right back).
Although exercise is certainly not the panacea for weight loss, there is no doubt that a substantial number of folks may experience very significant weight loss after taking up a regular exercise program.
I, however, have long suspected that the substantial weight benefits that these people experience has very little to do with the amount of calories burnt or, in other words, the [calories out] part of the equation.
Rather, I tend to favour the hypothesis that the weight-loss effects of exercise have more to do with the metabolic changes that result from the exercise (e.g. changes in insulin resistance, cortisol, sympathetic activity, etc.) and, perhaps even more importantly, the impact that exercise can have on ingestive behaviour.
Thus, I would not be surprised if the impact of exercise on mood and stress levels as well as the effects of exercise on self-esteem, improved sleep, and general well-being is in the end far more important for any weight loss associated with exercising than the actual amount of calories burnt.
Thus, I would predict that people in whom overeating is driven by stress, depression, poor self-esteem, or unrestorative sleep, will lose weight when they take up exercising – not because they are burning calories, but because they are eating less.
As a corollary, In people who are not overeating for any of the above reasons, exercise is far less likely to lead to weight loss – because it does not help them reduce their calorie intake.
Of course, if this hypothesis is true, it would easily explain why the same amount of exercise leads to weight loss in some people but not in others and why the amount of weight that some people lose with exercise simply cannot be explained by the amount of calories burnt.
In a paper just published in the Journal of Obesity, Jean-Phillipe Chaput and colleagues discuss exactly how physical activity can play a role in body weight regulation without actually affecting calories out.
The paper goes to great lengths to describe the many metabolic adaptations that occur in response to regular exercise and highlight how these adaptations rather than the actual number of calories “burnt” may explain many of the weight and health benefits of exercise.
As the authors also note:
“Regular exercise produces psychological improvements that may help buffering the harmful effects of stress. It has beneficial antidepressant and anxiolytic effect and, as shown in a recent meta-analysis, depression increases the risk to develop obesity. Exercise training also improves sleep patterns. Considering that bad sleeping habits is itself a stressor that has been associated with increased risk of obesity, physical activity can have a stress-buffer effect. There is also some evidence that exercise influences health-related behaviors, such as nutrition, and might help coping with life’s stress, particularly among high-risk individuals. Then, when practiced on a regular basis, physical activity could help breaking the stress-feeding habits.”
If the overall beneficial impact of exercise on body weight (in some people) has more to do with the metabolic changes, the stress relief, better sleep and other adaptations that affect food intake, then really the impact of exercise should not be measured (or predicted) by calories burnt.
In fact, the actual calories burnt may be completely irrelevant as shown in studies where stress-relief or mood management was found to significantly lower body weight. Thus, some people may well derive the very same weight-loss “benefits” of exercise by simply engaging in 30 minutes of quiet meditation or a daily leisurely walk in a restorative environment.
Focusing on “calories burnt” or even equating “calories burnt” with the potential weight benefits of exercise is misleading and frustrating.
As Chaput and colleagues nicely illustrate – the health benefits (whether weight related or not) of regular physical activity may have little to do with [calories out].
I wonder if my readers have noted how exercise affects their eating behaviour – I am guessing that while some folks actually end up “working up an appetite” (possibly resulting in weight gain) others may well have noticed that the stress relief and well-being that results from regular physical activity actually helps them eat less.
This would certainly support the idea that the weight-management benefits of exercise have substantially more to do with reducing calories in than increasing calories out.
Las Vegas, NV
Chaput JP, Klingenberg L, Rosenkilde M, Gilbert JA, Tremblay A, & Sjödin A (2011). Physical activity plays an important role in body weight regulation. Journal of obesity (Online), 2011 PMID: 20847894