Eating Less Reduces Fitness—But Exercise Preserves It

Healthnotes Newswire (January 4, 2007)—Eating fewer calories is one way to lose weight, but exercise needs to be part of the program to preserve muscle mass and physical fitness, a new study demonstrates.

For overweight and obese people, weight loss can reduce their risk of heart disease, diabetes, and some cancers. The formula for weight loss is simple: the calories burned in activity must exceed the calories taken in as food; in other words, eat less and exercise more.

When the diet does not provide the calories needed to produce the energy being spent, the body uses stores of fat and muscle to make energy. However, when muscles are used for energy it reduces their size and strength. For example, even the heart muscle can be a source of energy, but the consequence of using heart tissue for fuel would be a weaker heart and a lower exercise capacity.

The latest study to look at exercise and weight loss was published in the Journal of Applied Physiology. Thirty-four overweight adults participated in the one-year study and were assigned to either a low-calorie diet group or an exercise group. The goal of the diet group was to reduce calorie intake by 16% in the first three months and by 20% in the remaining nine months, while the task of the exercise group was to burn 16% more calories in the first three months and 20% more calories in the remaining nine months.

The two groups lost the same amount of weight by the end of the study—about 15 to 18 pounds. The differences were seen in muscle size and strength and in exercise capacity as measured by a treadmill test: all of these had decreased in the dieting group, but muscle mass and strength were preserved and exercise capacity increased in the exercise group.

Previous research has also found that calorie restriction alone results in loss of muscle mass and strength. The results of the current study suggest that exercise can prevent these muscle changes and also improve fitness (defined as the ability to perform physical tasks, not just recreational exercise).

“These findings suggest that during exercise-induced weight loss, the body adapts to maintain or even enhance physical performance capacity,” the study authors concluded. They continued, “It is important to note, however, that because caloric restriction resulted in substantial weight loss, the absolute requirement for many (but not all) common activities such as climbing stairs, also decreased. Therefore, from this perspective, the decreases in strength and aerobic capacity are proportional to the reduction in body weight, and a person’s capacity for weight-bearing exercise (in other words, walking, running, or climbing) would not likely be impaired by a low-calorie diet.”

Based on the findings of this study, regular exercise should be a component of every weight-loss program. In addition to enhancing weight loss, exercising can increase fitness and prevent a number of chronic diseases, regardless of its effect on body weight.

(J Appl Physiol 2006 Nov 9 [e-pub ahead of print])

Maureen Williams, ND, received her bachelor’s degree from the University of Pennsylvania and her Doctorate of Naturopathic Medicine from Bastyr University in Seattle, WA. She has a private practice in Quechee, VT, and does extensive work with traditional herbal medicine in Guatemala and Honduras. Dr. Williams is a regular contributor to Healthnotes Newswire.

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