London, Apr 15 (IANS): People who follow a low-calories diet in the hope of losing weight shouldn't bother unless they exercise as well, a new study has found.

"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 lead researcher Judy Cameron from Oregon Health and Science University.

To conduct the research, Cameron studied 18 female rhesus macaque monkeys. The monkeys were placed on a high-fat diet for several years. They were then returned to a low-fat diet 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, reports dailymail.co.uk

Surprisingly, there was no significant weight loss at the end of the month. 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," Cameron said.