Scientists at Oregon Health & Science University say they were surprised to find simply reducing caloric intake in monkeys by 30 percent was not enough to promote significant weight loss in one month.
The study, published in the American Journal of Physiology -- Regulatory, Integrative and Comparative Physiology, also finds a significant change in the activity levels for these monkeys and when caloric intake was further reduced in a second month, physical activity in the monkeys diminished even further.
"This research shows that simply dieting will not likely cause substantial weight loss," Judy Cameron, a professor of behavioral neuroscience at the OHSU School of Medicine, says in a statement. "Instead, diet and exercise must be combined to achieve this goal."
Cameron and colleagues fed 18 female rhesus macaque monkeys a high-fat diet for several years and then tracked weight and activity as calorie consumption was reduced. A comparison group of three monkeys fed a normal monkey diet and trained to exercise on a treadmill did lose weight, the study says.
The researchers suggest the body may have a natural compensatory mechanism that causes physical activity to decrease in response to decreased calories.