Diet Alone Does Not Lead to Significant Weight Loss

A new study has found that reducing caloric intake is not enough to promote significant weight loss, due to a natural compensatory mechanism that reduces physical activity in response to a reduction in calories.

Researchers at the Oregon Health & Science University (OHSU; Portland, USA) studied 18 female rhesus macaque monkeys, who were placed on a high-fat diet for several years. They were then returned to a lower-fat diet (standard monkey food) with a 30% reduction in calories. For a one-month period, the monkeys' weight and activity levels were closely tracked; activity was tracked with an activity monitor worn on a collar.

Researchers found that there was no significant weight loss at the end of the month, however, a significant change in the activity levels for these monkeys was observed. Naturally occurring levels of physical activity for the animals began to diminish soon after the reduced-calorie diet began; when caloric intake was further reduced in a second month, physical activity in the monkeys diminished even further. However, a comparison group of three monkeys, which was fed a normal monkey diet and was trained to exercise for one hour daily on a treadmill, did lose weight. The study was published in the April 2010 edition of the American Journal of Physiology (AJP) - Regulatory, Integrative, and Comparative Physiology.

"In the midst of America's obesity epidemic, physicians frequently advise their patients to reduce the number of calories they are consuming on a daily basis,” said lead author Judy Cameron Ph.D., a senior scientist at OHSU's Oregon National Primate Research Center. "This research shows that simply dieting will not likely cause substantial weight loss. Instead, diet and exercise must be combined to achieve this goal.”

"Food is not always plentiful for humans and animals and the body seems to have developed a strategy for responding to these fluctuations,” added Dr. Cameron. "These findings will assist medical professionals in advising their patients. It may also impact the development of community interventions to battle the childhood obesity epidemic and lead to programs that emphasize both diet and exercise.”

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