Don't worry about the deep-fried Mars bar, pints of stout, or the doner kebab on the way home from the pub. Just turn off that air-conditioning! A study published in the US International Journal of Obesity has found that air-conditioning results in us still wanting to eat despite baking temperatures. Or rather it stops us from feeling as if we do not want to eat. According to the researchers, if we are frying at work and home, we don't want to do the same to our food.

David Allison, professor of biostatistics at the University of Alabama at Birmingham, who led the study team, points out that over the past 25 years, since air-conditioning in the home has become more common in the US, rates of obesity have steadily risen. The aim of the research was to "investigate plausible contributors to the obesity epidemic beyond the two most commonly suggested factors, reduced physical activity and food marketing practices".

So air-conditioning becomes the new McDonald's, or couch-potato lifestyle. The research found that sweating burns calories (but probably no more than getting up to switch on the fan). However, being too cold makes your body work to achieve warmth, so really aggressive air- conditioning can help you lose weight. What is important, say the researchers, is that we do not sit around all day at work in the perfect temperature, as it could affect our waistlines.

I had a look into other factors which apparently cause obesity, and learned that just about everything makes you fat except, well, fat. Lack of sleep; the older your mum was when she had you; your weight at birth; having a fat partner; some chemicals in pesticides and plastics; the contraceptive pill; giving up smoking (but smoking in pregnancy can result in obese children, so you may stay thin but your kid might be a fatty); and being stressed (because then, according to yet another piece of research, you are less likely to resist an offer of wine or chocolate). Last year it was email that made you fat. A health and fitness expert deduced that because we no longer run up to the third floor to pass on gossip, or hike up to human resources to find out why we've been underpaid because we just have to send an email, we are exercising less.

Currently more than 40% of British women are trying to diet, which could lead to hundreds of thousands of us being trapped in stiflingly hot work-places while slimmers try yet another miracle cure. Would anyone really rather be half-dead with heat exhaustion than carry a few extra pounds?

So, those of you who are in constant battle with colleagues who tell you to turn off the air-conditioning because it spreads legionnaire's disease are actually covert slimmers. Expose their true motive at the water cooler. They can suffer for their size 10s, but why should the rest of us join them?