One of the most interesting things about exercise is that it results in important health improvements even in the absence of weight loss. For example, just a single session of exercise can result in improved insulin sensitivity, increased levels of HDL cholesterol (aka the “good” cholesterol) and reductions in plasma triglyceride levels – all tremendously important markers of disease risk. In addition to these metabolic changes, new research by our friend and former labmate Lance Davidson suggests once-again that exercise can also prevent the accumulation of abdominal fat, independent of changes in overall body fat percentage.
The new study, published in the current issue of the Journal of Physical Activity and Health, examines the prospective association between physical activity and body fat in a group of healthy, non-obese women. Physical activity, body fat percentage, waist circumference and food intake were assessed at baseline and again 20 months later (there was no intervention per se, just pre and post measurements). Compared to baseline, physical activity decreased in the group as a whole, while body weight, body fat percentage, and waist circumference all increased – none of which is terribly surprising. But that’s the information for the group as a whole – the interesting results come when participants were grouped according to whether or not they increased, maintained or decreased their level of physical activity during the 20 month study (see graph below).
As you can see, individuals who decreased their physical activity levels increased their waist circumference by about 2.5 centimeters (~1 inch) during the 20 month study. Surprisingly, individuals who maintained their physical activity levels also increased their waist circumference. Finally, individuals who increased their physical activity level saw no change in waist circumference during the study. These group differences remained significant after controlling for confounders including baseline physical activity, energy intake, and overall change in body fat.
So what’s the take-home message? Increasing your physical activity level appears to prevent the accumulation of abdominal fat, regardless of what is happening to your body weight or overall level of body fat. This is tremendously important given the strong links between abdominal fat and health risk, and because many people quit their exercise program when they fail to see a change in the number on the bathroom scale. These findings fit with past research, which has suggested that structured exercise preferentially reduces visceral fat, even when body weight does not change at all. I’m not 100% clear why waist circumference increased in individuals in the current study who maintained their physical activity levels, and I’d be interested to hear if anyone has any thoughts on that.
So remember, regardless of what is happening to your weight or even your body fat percentage, increasing your level of physical activity still results in measurable improvements in body fat distribution and overall health.