Overweight by osmosis

Your roomies, colleagues and boyfriend could be making you fat without you even realising it...

When Jess, a 27-year-old account manager, got a job at a new firm, she put on 10kg in eight months. "It was the culture there," she explains.

"My colleagues and I were always having big, unhealthy corporate lunches, going to the pub after work, and hitting the vending machine. If I tried to resist I'd be met with a barrage of 'Oh, go on. One Mars Bar won't kill you!'"

Ellie, a 24-year-old nurse, had a similar situation. "At my last sharehouse, I put on 6kg in three months," she says. "My flatmates were pizza-and-beer people. I wanted to be social, so, every night, I ate the grease, downed the booze, and quickly watched my belly expand."

Social sabotage

Dr David Crawford, professor of exercise and nutrition sciences at Deakin University in Australia, hears these stories often. "When people are unsupportive of a friend's or loved one's healthy choices, it's known as 'social sabotage'," he says. Social sabotage isn't malicious — it's usually unconscious — but it makes a girl's health goals nearly impossible to achieve.

Why? "Because humans are social animals, with an in-built need to please the pack," says Crawford. We're easily influenced by those close to us — for example, if you come home and say to your partner, "I'm going for a run. Wanna come?", and he responds, "No, don't go. I haven't seen you all day", chances are you'll ditch your running shoes.

Breaking the cycle

After eight months of work-related weight gain, account manager Jess got tough with her colleagues: "I called the vending machine 'The Fat Box' and steered away from pub lunches. I got flack at first, but the guys got used to it. I'd rather be known as a 'food fascist' than be carrying those extra 10 kilos."

Dr David Crawford's ideas for living an active lifestyle without being negatively influenced by others:

• Tell your mates that you're on a health kick/detox. Or let them know about the goal you're working towards: "I'm in training for the marathon/the Kokoda trail/fitting into last year's pants."

• Don't enter into discussions about whether or not you're going out to exercise. Just cheerfully say, "Bye!", and head for the door.

• Instead of suggesting food- and booze-centric activities, invite friends out for bike rides and swims, or walk your dogs.