Simply cutting down on calories won't help you reduce flab, says a new study.
This appears to be due to a natural compensatory mechanism that reduces a person's physical activity in response to a reduction in calories.
"This research shows that...instead, diet and exercise must be combined to achieve this goal," said Judy Cameron, professor of behavioural neuroscience and obstetrics & gynaecology at the Oregon Health and Science University (OHSU).
Cameron and OHSU post-doctoral fellow Elinor Sullivan, studied female rhesus macaque monkeys at the Oregon National Primate Research Centre.
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," said Sullivan.
"When caloric intake was further reduced in a second month, physical activity in the monkeys diminished even further," she added.
A comparison group of 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, said an OHSU release.
"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.