Active Voice: Should Aerobic Exercise be a Primary Strategy for Weight Loss?
By Nicholas Broskey, Ph.D., and Leanne Redman, Ph.D.
The health benefits of aerobic exercise cannot be over emphasized in preventing cardiometabolic diseases. Exercise interventions are also commonly proposed to help lose weight and seem efficacious for weight loss maintenance. In the U.S., 30 minutes of moderate-intensity exercise per day for five days per week (150 minutes total per week) is recommended for health benefits and possibly improved weight control. To support weight loss efforts, the recommended dose increases to 200 to 300 minutes per week for individuals with overweight/obesity. However, when exercise interventions are prescribed without reductions in caloric intake, they often result in less weight loss than expected. Thus, the use of exercise alone as an effective strategy for weight loss can be challenged.
Total daily energy expenditure, the number of calories burned in a day, increases in proportion to the dose of exercise. However, it has been proposed that the contribution of exercise to total daily energy expenditure may have limits. The constrained total energy expenditure model posits that increases in energy expenditure due to exercise eventually plateau, due to decreases in other components of daily energy expenditure. The extent to which the energy deficit induced by exercise is counteracted by the body defending against weight loss is not well understood.
The Examination of Mechanisms of Exercise-induced Weight Compensation (E-MECHANIC) study was designed to identify mechanisms responsible for unsuccessful weight loss with increased exercise energy expenditure. Overweight, sedentary individuals were randomized to either an aerobic exercise group or a healthy living control group with no exercise intervention for 24 weeks. The main findings were the exercise-induced weight loss was significantly less than expected. This indicates a compensation in the form of increased energy intake or a decrease in energy expenditure in other components of daily energy expenditure.
In our recent study published in the October 2021 issue of Medicine & Science in Sports & Exercise®, we conducted an ancillary to E-MECHANIC in 42 subjects. This study investigated what is changing in the other components of daily energy expenditure that may result in unsuccessful weight loss. This novel study combined the gold standard for daily energy expenditure, the doubly labeled water method, with a 24-hour measurement in a whole-room respiratory chamber.
Individuals randomized to an exercise dose recommended for weight loss (20 kcal per kilogram of weight per week) only lost half of the expected amount of weight. They had a slight increase in total daily energy expenditure due to the exercise. However, they also had a reduction in 24-hour energy expenditure concomitant with an increase in sedentary time in the respirator chamber. Thereby, the net contribution of exercise to daily energy expenditure was small. Exercise at this dose does not promote weight loss in all people as energy burned in exercise may be compensated by overall energy conservation. Personal trainers, coaches and those professionals prescribing exercise for weight loss should also incorporate dietary caloric restriction. Additional work is needed to determine whether improved exercise efficiency, including cellular adaptations, may explain the constrained energy expenditure model in humans and why some individuals may be protected from exercise-induced weight loss.
About the authors:
Nicholas Broskey, Ph.D., has a background in exercise physiology and metabolism. He is an assistant professor in the department of kinesiology at East Carolina University, an affiliated faculty member with the East Carolina Diabetes and Obesity Institute, and a member of ACSM. Dr. Broskey’s research integrates whole body physiology with both cellular and sub-cellular metabolism. Particularly, he is interested in how exercise interventions can help ameliorate conditions of metabolic disease through changes in skeletal muscle bioenergetics.
Leanne Redman, Ph.D., is a professor in the Division of Clinical Sciences at Pennington Biomedical Research Center in Baton Rouge, Louisiana. Dr. Redman’s research focuses on understanding the role of metabolism in body weight regulation. Her work studies body weight changes in the context of weight loss, weight gain and in response to exercise, surgery, pregnancy and pharmacotherapy.
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