Metabolic Improvements Not Likely After Exercise?

by Ryan Halvorson

Making News:

Fitness professionals often suggest to clients that a benefit of exercise is its capacity to boost metabolic function. A recent study, however, has put that suggestion to task. According to research published in the April issue of Exercise and Sport Sciences Reviews (2009; 37 [2], 93–101), the assertion that an exerciser burns fat up to 24 hours after a workout may not be completely accurate.

The authors reviewed several studies to compare fat oxidation on exercise and nonexercise days in moderately active people and endurance athletes. The exercisers performed either low-intensity or high-intensity cycling for less than an hour, or did not exercise at all. Using whole-room indirect calorimetry, the authors determined that participants burned up to 400 calories during exercise, but that caloric expenditure did not last postexercise. Though fat oxidation did take place during the exercise bouts, there was no evidence to support heightened metabolic function after workout completion. “To our surprise, we have found that exercise has little, if any, effect on 24-hour fat oxidation,” stated the authors.

They went on to suggest that a more significant factor in fat oxidation involves carbohydrate intake. “Ingesting as little as 60 grams (g) of carbohydrate during the hour before exercise can reduce lipolysis and fat oxidation during subsequent exercise, and the increase in fat oxidation during exercise can be blunted for up to 6 hours after consumption of a meal.” The authors conceded that alternate exercise methods might solicit alternate results.

Jade Teta, ND, CSCS, co-owner of Metabolic Effect in Winston-Salem, North Carolina, believes this study offers insights into optimal fat loss. “First and foremost it makes very clear that diet is most important for fat loss and directly impacts the ability of exercise to have a fat-burning effect,” states Teta. “In my opinion, a diet made up of more than 50% carbohydrates is a high- carbohydrate diet, and would create a significant impediment to fat loss regardless of exercise, due to the insulin effect.”

Similarly to the authors’ suggestion, Teta believes that the exercise methods employed in the study may be partly to blame for limited postexercise fat oxidation. “Since this review focused on moderate-intensity aerobic exercise and spent little time analyzing higher-intensity exercise, the only conclusion we can draw is that moderate-intensity aerobic exercise provides little metabolic advantage aside from the calories it burns during activity.”

So what’s the take-home message? The study gives great insight into what works and what does not, says Teta.

For more information on exercise and its effect on metabolism, check out the following articles available online in the IDEA Library (www.idea fit.com/fitness-library):

“Controversies in Metabolism,” by Paige Kinucan and Len Kravitz, PhD, January 2006 IDEA Fitness Journal
“Yes! You Do Burn Fat During Resistance Exercise,” by Lawrence Herrera and Len Kravitz, PhD, April 2009 IDEA Fitness Journal