There’s a common thought out there that overweight individuals are eating too much, or not exercising enough (or both). However, when it comes to matters that pertain to body weight, things are not necessarily as simple as they seem. For instance, my experiences in practice have led me to believe there are individuals wandering this planet who despite eating relatively modest quantities of food, nonetheless still carry more fat than they perhaps ought to. One explanation here is that these individuals have a metabolism that is simply not firing on all cylinders. Some of these individuals may have biochemical evidence of this in the form of tests which indicate low thyroid function. Others may have ‘normal’ thyroid function tests, but that is certainly no guarantee that their metabolism is functioning optimally. Others still may have a ‘sluggish’ metabolism for reasons that have nothing to do with the functioning of their thyroid gland.
Similarly, being overweight is not necessarily a sign of slothfulness. For one thing, there what some may think a surprising dearth of scientific evidence which supports the concept that exercise is effective for the purposes of weight loss. In fact, there is good evidence which suggests that exercise is quite ineffective in this regard [1,2]. One explanation for this is that the calorie burn during all but the most intense and prolonged exercise is quite small. Another explanation is that people who exercise more tend to eat more too. Because of these factors, it’s just not that easy pushing oneself into calorie deficit with exercise in the long term.
If exercise is not particularly effective in terms of inducing weight loss, then how important is activity in terms of maintaining a healthy weight? In theory, it shouldn’t matter too much. The American Journal of Clinical Nutrition recently published on-line a paper which assessed the relationship between energy expended during exercise and weight in two groups of women: native Nigerians and African Americans [3]. The obesity rate in the Nigerian women was 7 per cent, compared to 50 per cent in the African Americans. This sort of discrepancy is often put down, at least in part, to the supposedly higher energy expended in activity and exercise in the developing world compared to developed parts of the globe. Yet, this did not seem to hold true for the women in this study: the energy expended during activity in the two groups was about the same. Physical activity levels were not significantly different either.
This is an interesting observation, but not necessarily as meaningful as assessing the relationship between activity-related energy expenditure and body weight in a single population. Using a more homogenous group as your subjects generally yields more meaningful and relevant observations than those obtained by looking across two quite different groups. Thankfully, the researchers responsible for this study assessed the relationship between between activity-related energy expenditure and weight over a 3-year period. In neither group did the researchers find any relationship between activity-related energy expenditure and change in weight. In other words, levels of activity did not appear to have any influence on weight gain over the course of the study.
According to the authors their data suggest that “levels of energy expended during activity do not have a large influence on age-related trends in adiposity.”
This of course does not mean that activity is not a good idea. The authors themselves point to research which has found that activity is associated with improve physical fitness and cardiovascular health, as well as reduced mortality. However, the pointedly end their study by stating “the role of small variations in AEE [activity energy expenditure] as part of daily activities in a public health strategy to prevent obesity remains very much in doubt. In defining public health policy , it will be crucial to discriminate between the known health benefits of physical activity and the presumed effect on weight change.” In other words, let’s not be telling people that activity is crucial for maintaining a health weight if we don’t have any good evidence which shows this to be true.
References:
1. Votruba SB. The role of exercise in the treatment of obesity. Nutrition
2. Shaw K, et al. Exercise for overweight or obesity. Cochrane Database of Systematic Reviews 2006, Issue 4.
3. Luke A, et al. Energy expenditure does not predict weight change in either Nigerian or African American women. Am J Clin Nutr [Epub 3rd December 2008]
