Does Exercise Really Help You Lose Weight?

Health experts advise people to exercise in order to lose weight and stay thin. For example, the American College of Sports Medicine, as well as the American Heart Association, both recommend at least 60 to 90 minutes of daily physical activity in order to lose weight (1). The Department of Health and Human Services recommends that adults exercise moderately for at least 150 minutes per week or intensely for at least 75 minutes per week (2).

However, outside studies have not confirmed that exercise and weight loss are linked. For example, Dr. Timothy Church's group at Louisiana State University published a study on 4 groups of overweight women who either did not exercise, or who were assigned to a personal trainer for 72, 136, and 194 minutes of exercise per week for a period of 6 months. The women who exercised the most did not lose the most weight. Also, some women in all 4 groups actually gained 10 pounds or more (1).

Another study, performed at the Pennsylvania State University, assigned groups of men to a 12 week program of diet or both diet and exercise. The men who dieted and exercised (3 times per week for 50 minutes) lost only one pound of fat more than the men who only dieted (3).

The contradictory results of such studies are due to a two part problem with exercise. To begin with, 1 pound of body fat is the equivalent of about 3,600 calories. In order to lose 1 pound of body fat, then, a person must burn 3,600 calories more than he or she ingests. An aerobic exercise, such as walking briskly at 3 miles per hour for 30 minutes each day, burns 150 calories (with 1 mile being equal to 100 calories). This means that a person needs to maintain this walking regimen for nearly 3.5 weeks before 1 pound of body fat is lost. In most cases, such a person will be disappointed by this slow weight loss and give up on his or her exercise regimen.

Slow weight loss from exercise alone is just one part of the problem. The other part has to do with appetite. Most individuals will experience an increase in appetite after exercising. Lipoprotein lipase (LPL), a hormone involved in fatty acid metabolism, will spike in muscle cells during exercise (4). This occurs so that fatty acids can be converted by LPL into energy for the muscle cells. Meanwhile, fatty tissue will decrease as its fatty acid stores are used up during exercise. Once the exercise period has ended, the LPL will shuttle back to the fatty tissue in order to restore any remaining liberated fatty acids into fat. The fatty tissue will focus on replenishing itself back to pre-exercise levels and so will induce hunger. As a result, the person who just finished burning off 150 calories from walking for 30 minutes may now be hungry enough to ingest 450 calories from a pizza slice.

The lack of significant weight loss from exercise may also be sabotaged by psychology. A person who just finished walking several miles may rationalize eating an extra serving of ice cream for dinner. This extra serving, however, undoes all the calorie loss incurred during the walk. Alternately, that person may become more sedentary once he or she arrives home.

In conclusion, while exercise is of great benefit to a person's cardiovascular health, skeletal strength, etc., it may not necessarily be the best solution for weight loss. Instead, diet may play a much greater role in losing weight and keeping it off. Furthermore, a person who is hoping to lose weight via exercise should realize that such an effect occurs only when food intake is reduced.

References:

1. Why Exercise Won't Make You Thin http://www.time.com/time/health/article/0,8599,1914857,00.html

2. Does Exercise Really Make You Healthier? http://www.scientificamerican.com/article.cfm?id=does-exercise-really-make

3. Kraemer, W.J., Volek, J.S., Clark, K.L., Gordon, S.E., Puhl, S.M., Koziris, L.P., McBride, J.M., Triplett-McBride, N.T., Putukian, M., Newton, R.U., Hakkinen, K., Bush, J.A., & Sebastianelli, W.J. (1999). Influence of exercise training on physiological and performance changes with weight loss in men. Medicine and Science in Sports and Exercise, 31, 1320-1329

4. The Scientist and the Stairmaster http://nymag.com/news/sports/38001/