Exercise and energy balance: going to extremes to show that body weight is not the best outcome

Although we all agree that obesity has reached epidemic proportions worldwide, there is still a heated debate in the literature as to whether we should focus on diet or on physical activity/ exercise to deal with the problem. Some investigators have suggested that the obesity epidemic is largely explained by the increase in food intake (1). In addition, it is frequently mentioned in the media that exercise is pretty much useless for losing weight and rather that we should focus on diet and energy intake to achieve body weight loss (2). On the other hand, matching energy intake to expenditure becomes a challenge among very sedentary individuals (3). Because a sedentary lifestyle has become the norm in North America and in many parts of the world, it is of little surprise that food intake would then largely drive the obesity epidemic at the population level. When daily energy expenditure is low, there is no buffer to combat the excess calories provided by an energy-dense, highly refined diet, which is consumed by so many of us. It is also documented that previously obese individuals who have been successful in maintaining a reduced body weight have a lifestyle that includes high levels of physical activity (4). Thus, it does not take a rocket scientist to figure out that the low level of physical activity that characterizes one-third of our population (5) makes many individuals exquisitely susceptible to a potentially obesogenic diet. As a consequence, being myself a busy scientist confined to countless hours of sedentary sitting time (writing papers and grants and holding meetings with colleagues and students), I have tried to make sure that there are 1–2 h/d devoted to endurance exercise despite my busy agenda. The objective of putting these daily periods of vigorous and prolonged physical activity in my schedule has been 2-fold: 1) to induce the expression of numerous genes that confer protection against the development of metabolic diseases and 2) to significantly increase my total daily energy expenditure, providing a buffer against occasional exposure to our ubiquitous obesogenic diet. We have previously shown that such a strategy contributes to mobilizing dangerous visceral adipose tissue/ectopic fat depots and improves numerous cardiometabolic risk markers (6). With age, I have moved from being a long-distance runner to a recreational biker, devoting at least 10 h/wk to road cycling. Of course, this volume of exercise is way beyond the recommended 150 min of moderate physical activity/wk (7), but this level of exercise-related energy expenditure has clearly provided me protection against my potentially obesogenic environment (very sedentary work and not always consuming an optimal diet). Thus, contrary to the notion disseminated in the media that exercise is useless for remaining in energy balance, experimental evidence and personal experience have convinced me that a substantial physical activity/exercise prescription is a win-win approach, not only providing protection against obesity but, more importantly, generating the metabolic flexibility compatible with cardiometabolic health. In this regard, the article by Rosenkilde et al. (8) published in this issue of the Journal provides extreme energy expenditure data that are very relevant to the above debate. In this spectacular study, the daily exercise “prescription” was huge because the authors wanted to test the ability of these elderly and fit recreational cyclists to match their energy intake to their energy expenditure. Despite substantially increasing their intake, the cyclists could not fully match it to their large energy expenditure. These results suggest that a very large exercise prescription reduces the probability of an individual being in positive energy balance, despite what can be considered by any standard as consuming a tremendously large amount of energy. This notion is compatible with the concept put forward by Hill et al. (9) that the body better regulates its energy balance at a high level of energy turnover compared with very sedentary individuals who, as mentioned before, are very prone to being in positive energy balance. Another striking and important finding of the study byRosenkilde et al. (8) is that despite the huge energy expenditure associated with the 2700-km bike expedition, participants did not lose weight. However, this lack of change in body weight was misleading in terms of energy balance. Indeed, the cyclists lost 2.2 kg of body fat while gaining 2.5 kg of fat-free mass, a remarkable finding considering that this was observed