Reducing caloric intake is ineffective unless accompanied by an increase in exercise, according to researchers.
This appears to be due to a natural compensatory mechanism that prompts the body to cut back its physical activities in response to a reduction in calories.
“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. This research shows that simply dieting will not likely cause substantial weight loss. Instead, diet and exercise must be combined to achieve this goal,” said Judy Cameron, a senior scientist at Oregon Health & Science University’s national primate research center, and a professor of behavioral neuroscience and obstetrics & gynecology in the OHSU School of Medicine.
To conduct the research, Cameron studied 18 female rhesus macaque monkeys at the Oregon National Primate Research Center. The monkeys 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 percent reduction in calories. For a one-month period, the monkeys’ weight and activity levels were closely tracked. Activity was tracked through the use of an activity monitor worn on a collar.
“Surprisingly, there was no significant weight loss at the end of the month,” explained Sullivan. “However, there was a significant change in the activity levels for these monkeys. 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.”
A comparison group of three monkeys was fed a normal monkey diet and was trained to exercise for one hour daily on a treadmill. This comparison group did lose weight.
“This study demonstrates that there is a natural body mechanism which conserves energy in response to a reduction in calories. Food is not always plentiful for humans and animals and the body seems to have developed a strategy for responding to these fluctuations,” added 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.”
The research is published in the April edition of the American Journal of Physiology Regulatory, Integrative and Comparative Physiology.