Keeping a busy social life amongst lots of friends may keep people slimmer than spending hours on a treadmill, according to scientists.
They say that socialising and meeting with friends helps boost levels of 'brown fat' in the body which burns calories to generate heat.
Living in a stimulating, social environment was found to reduce abdominal fat in mice by half over four weeks, even if they ate more.
US researchers say that social stimulation aids weight loss by converting white fat into brown.
White stores calories and makes us fatter, while brown burns energy to generate heat.
Converting white fat into brown is notoriously difficult, normally requiring long term exposure to cold conditions or activating part of the body's nervous system.
However, scientists from Ohio State University now think that having a busy social life is an even more effective way of changing white fat into brown.
The team came up with their theory by studying the effects of various living environments on mice.
Those who lived alongside a greater number of mice, had more space and toys to stimulate them lost far more weight over the course of the study than their 'couch potato' counterparts.
Increased levels of brown fat may also be attributed to an increase in a brain chemical called brain-derived neurotrophic factor [BDNF] found in the sociable mice.
Study author Dr Matthew During, whose team's findings appear in journal Cell Metabolism said: I'm still amazed at the degree of fat loss that occurs.
'The amount that comes off is far more than you would get with a treadmill. TIt's usually hard to induce the switch from white to brown fat.
'It takes months of cold - you really have to push - and it doesn't induce brown fat to the same degree as what on the surface appears to be a relatively mild change in physical and social environments.'
Explaining how new technology had threatened face-to-face socialising, he added: 'It's not just a sedentary lifestyle and high calorie foods, but an increasing lack of social engagement.'
Co-author Dr Lei Cao said: 'After four weeks in the enriched environment, the animals' abdominal fat decreased by 50 per cent.
'We often think of stress as a negative thing, but some kinds of stress can be good for your health.
'In fact, the enriched housing is more taxing for the animals as they have to deal with each other and with a more complex environment.'
Dr Cao added: 'The new result may offer insight into studies showing a link between loneliness and ill health.
'Loneliness is a profound factor for cancer and death; it's on par with cigarette smoking. Social engagement is very important.'
Rakesh babu R