Do The Math
09/26/2012 09:09AM ● Published by Aimee Cormier
New Approach Explains Effect Of Exercise On Weight Loss
Courtesy of Pennington Biomedical Research Center
With the obesity epidemic in full swing, Americans are increasingly told by government health agencies and major medical associations to increase exercise levels to promote weight loss. Despite dozens of controlled trials, the effects of exercise on the magnitude of produced weight loss remain uncertain. Many studies fail to show any significant weight loss. The basis for low weight loss in response to exercise remains unknown.
In a paper published online on June 11, 2012 in Obesity Reviews, Pennington Biomedical researchers, along with lead author Diana Thomas, Ph.D. of Montclair State University and other colleagues at Duke University, Maastricht University, and the Technical University of Lisbon, provide the most advanced attempt to explain why individuals do not lose more weight from an exercise intervention. This study applied the first law of thermodynamics to critically examine all possible explanations for low weight loss in response to exercise in 15 closely supervised exercise experiments.
Specifically, the study authors calculated the change in body energy resulting from an exercise intervention. The change in body energy is determined by summing the energy lost in fat and the energy lost in lean (muscle), both of which are typically measured in exercise experiments. Theoretically, the change in body energy should equal the additional amount of energy expended from exercise, that is, if an individual expends an additional 300 kcal, a 300 kcal loss of energy should decrease from their body. However, the study authors found this was not typically the case. In fact, the magnitude of body energy lost was generally less than the amount expended from exercise.
The discrepancy can be explained by only four possible mechanisms:
1. A decrease in resting energy expenditure beyond those accounted for at reduced weight (referred to as metabolic adaptation).
2. An increase in dietary intake
3. A decrease in daily life non-exercise activity due to fatigue
4. An increase in lean mass.
The authors discovered that the loss of lean mass in response to exercise is significantly less than predicted by these existing models.
The authors systematically explored each possibility and arrived at several new surprising findings.
Metabolic adaptation is a well-established phenomenon in dieters, however, the prevailing thought is that exercise protects against metabolic adaptation and in fact, even serves to increase metabolic rate at rest “revving the metabolism.” The authors examined a unique experiment conducted in seven pairs of male twins who were directly supervised in confined conditions and exercised while dietary intake was held constant. The authors found the evidence for the existence of metabolic adaptation in response to exercise, debunking the notion that exercise “revs your metabolism.”
The authors additionally found that individuals performing vigorous exercise tend to increase dietary intake, providing rigorous mathematical support to recent experiments examining the effects of exercise performed at high levels.
One major study finding is that existing models overestimate weight loss due to their reliance on conclusions from calorie restriction experiments. The authors discovered that the loss of lean mass in response to exercise is significantly less than predicted by these existing models. The study authors corrected the models to account for less loss of lean mass and increased loss of fat mass during exercise.
These observations have considerable implications for adults trying to lose weight through exercise by clearly defining the amount of expected weight loss from an exercise program and by identifying how body weight changes in response to exercise. These findings will help health care providers and individuals set realistic weight loss goals in relation to exercise. These findings help us to understand the weight-effects of exercise but do not negate the beneficial effects of increased physical activity on health.
The study was led by Dr. Diana Thomas from the Center of Quantitative Obesity Research at Montclair State University, who collaborated with Pennington Biomedical researchers Leanne M. Redman, Ph.D.; Corby K. Martin, Ph.D.; Claude Bouchard, Ph.D.; Michaela Vossen, Ph.D.; Timothy Church, M.D., M.P.H., Ph.D.; and Steven B. Heymsfield, M.D. Other collaborating institutions in the U.S., the Netherlands, and Portugal include: Duke University (William E. Kraus, M.D. and Cris A. Slentz, Ph.D.), Masstricht University (Klaas Westerterp, Ph.D.), and the Technical University of Lisbon (Analiza M. Silva, Ph.D.).
The Pennington Biomedical Research Center is at the forefront of medical discovery as it relates to understanding the causes of obesity, diabetes, cardiovascular disease, cancer and dementia. It is a campus of the Louisiana State University System and conducts basic, clinical and population research. For more information, see www.pbrc.edu.