Do you want to lose weight? Well, forget the gym and the fad diets, because there's a very simple way to shed the pounds: stand up while you teach.
Research published in the academic journal Science suggests that simply standing more and sitting less could help you lose as much as 15kg a year.
The study, which was carried out by Dr James Levine of the Mayo Clinic in Rochester, Minnesota, investigated how often mildly obese people stand during a normal day, compared with their leaner colleagues.
The investigators picked self-confessed "couch potatoes" for their research. The fat and thin subjects, none of whom exercised much, were fitted with special instruments to measure body posture and movements continuously for 10 days. The researchers found that obese people sit for an average of 2.5 hours per day more than their lean colleagues, a difference that saves about 350 calories in energy expenditure. They then calculated that if the mildly obese were to stand up as much as their counterparts, they could lose 15kg a year.
Dr Levine says that most people don't realise that only around 10 to 20 per cent of daily energy is expended on planned physical activity, such as walking or running. Most of the calories we burn are instead used by our resting metabolic rate (the energy needed for body maintenance, including cellular metabolism and breathing, circulation, and tissue oxygen uptake), thermogenesis (the heat generated from burning food that we need to stop freezing to death), and muscle activities such as fidgeting, muscle tone, standing and maintenance of posture.
And yet most people think only of structured exercise when they decide to lose weight, despite the fact it has only a limited impact. In his paper, Dr Levine reminds us that the "energy gap" used to explain the increased prevalence of obesity is 100 to 200 calories per day, which suggests that only a small sustained change in either energy intake or energy expenditure would prevent obesity in most of us.
But why do some of us prefer standing to sitting? Is there something about being overweight that makes us sit more? Does it, for instance, put more stress on our joints, which hurts? Some endocrinologists or hormone specialists have even suggested that fat cells might release a hormone that encourages people to sit more and be less active.
To test these theories, Dr Levine and his colleagues encouraged their subjects to either gain or lose weight to see if the changes altered the amount of time they spent sitting or standing. Intriguingly, they didn't - suggesting these are deeply ingrained habits that might even be genetic; an idea backed by previous research that found that average daily standing time is more similar among siblings than among unrelated individuals.
But if how much we stand is a deeply ingrained habit, then increasing standing in order to lose weight might require profound changes in our environment. Perhaps teachers keen to lose weight should keep temptation out of the way and remove their chair from their classroom.
Professor Raj Persaud is a consultant psychiatrist at the Bethlem Royal and Maudsley hospitals in London. His latest book is The Motivated Mind (Bantam Press, pound;12.99). Email: firstname.lastname@example.org