Active Voice: Exercise or Calorie Restriction to Lower Blood Triglycerides Levels?
By Labros S. Sidossis, Ph.D., and Elena Bellou, Ph.D.
Viewpoints presented in SMB commentaries reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Labros Sidossis, Ph.D., is professor of medicine and nutrition and metabolism at the University of Texas Medical Branch (UTMB), Galveston, USA. A member of ACSM, he is Director of Obesity Research at the Sealy Center on Aging at UTMB. Dr. Sidossis also is Professor in the Department of Nutrition and Dietetics, Harokopio University, Athens, Greece. His research interests include obesity and
lipid metabolism, lifestyle interventions to promote health and brown adipose tissue metabolism.
Elena Bellou, Ph.D. is clinical dietitian and post-doctoral fellow in the Department of Nutrition and Dietetics, Harokopio University, Athens. Her scientific interests relate to the regulation of human lipid metabolism, particularly effects of lifestyle interventions on lipoprotein triglyceride kinetics.
In this commentary, Dr. Sidossis and Dr. Bellou present their views related to the research report which they and their colleagues published in the March 2013 issue of Medicine and Science in Sports and Exercise® (MSSE).
Lifestyle changes are the first line of therapy for metabolic abnormalities such as hypertriglyceridemia, or elevated triglycerides. Exercise is particularly efficient in improving the lipid profile in humans; even a single bout of exercise can acutely decrease the blood triglyceride concentration. However, for this to work, exercise should result in a negative energy balance. When food is increased to compensate for the energy lost during exercise, the hypotriglyceridemic effect of exercise is lost.
Decreased energy intake (hypocaloric diet) also has been shown to lower blood triglyceride levels. However, we do not know: a) if exercise and diet affect triglyceride metabolism in the same way; and b) if the effect of exercise works only through negative energy balance, or also through some other mechanism.
To find out, we evaluated the effect of negative energy balance, induced by either a single bout of aerobic exercise (~2 hours at 60% VO2peak) or calorie restriction, on very low density lipoprotein-triglyceride (VLDL-TG) metabolism in healthy women (see our recent MSSE report). We found that a single bout of exercise reduced VLDL-TG concentrations by ~30%. This was accomplished by both a decrease in VLDL-TG secretion from the liver and an increase in VLDL-TG clearance from blood. However, calorie restriction, designed to induce the same negative energy balance as exercise (i.e., 500 kcal), had no effect on triglyceride metabolism. Therefore, it appears that the hypotriglyceridemic effect of exercise is not merely the result of negative energy balance, but instead is specific to muscular contraction. In this respect, acute exercise appears superior to calorie restriction in lowering blood lipid levels, at least over the short term.
We also found that, to lower blood lipid levels, our subjects (all lean women) needed to exercise (vigorous walking) for approximately two hours. Available literature indicates that the recommended duration of 30 minutes for an exercise bout does not improve plasma TG levels in healthy subjects, at least not after a single bout. However, obese and/or hypertriglyceridemic subjects may require less exercise to lower blood lipid levels.
However, men and women seem to respond to exercise differently, in respect to triglyceride metabolism:
- In women, exercise decreases VLDL production and increases VLDL clearance;
- In men, the decrease in triglyceride concentration results from increased clearance only.
These findings may lead us to find appropriate lifestyle interventions to improve plasma TG metabolism.