If you're reading this sitting down, stand up immediately, you disgusting blob (no offence). Do some heel raises to improve your core strength. Would it kill you to march on the spot? You'll activate the protein lipase, which sucks fat from bloodstream into muscles, where it can be burned off if you throw in a few star jumps now and then.

Aim to keep a steady walking pace of 1.3 to 1.4 mph for the rest of this article. Your brain may atrophy, but that'll be my fault. Incidentally, I wrote this while standing at a lectern like Donald Rumsfeld. Think how much worse the world would be today if Rumsfeld had worked sitting down.

In Horizon: The Truth About Exercise (BBC2), presenter Michael Mosley repeated the mantra "The chair is a killer, the chair is a killer." His father had type two diabetes and he didn't want to continue that family tradition. But he also detested gyms. What should he do? Mosley put on a pair of what scientists call "fidget pants" that monitored how much his sedentary self moved by comparison with a waitress. Her lifestyle – cycling to work, criss-crossing the cafe with trays – proved ideal to boost something called "non-exercise activity thermogenesis" (Neat).

James Levine, the doctor who developed Neat, argues that the energy burnt off by exercises such as jogging or at the gym is negligible compared with natural movements like fidgeting, bending, walking and shaking your fist at doctors. In the past, Levine has removed chairs from offices, replacing them with desks attached to treadmills, and installed tracks on office perimeters to facilitate "walking meetings". If only the resultant human energy (rage at not having a chair, for example) could be harnessed to the national grid, corporate fuel bills would be slashed.

Later Levine revealed he had found negligible activity in Mosley's fidget pants. Mosley had been sitting for 12 hours-plus a day. Not unusual – the average Briton sits for 12 to 14 hours a day. Rolling your eyes sarcastically doesn't count as a workout.

So Mosley started walking and cycling more. He also got involved with scientists at Nottingham and Birmingham universities who have developed something called Hit (High-Intensity Interval Training). Their incendiary idea is that three minutes of intense workouts a week can burn more fat than longer workouts. Mosley put this to the test by cycling on an exercise bike as hard as he could for 20 seconds as his son grinned. TV always likes seeing a middle-aged man suffer, but his son enjoyed it more. Mosley repeated this twice, and the whole training regime three times a week. Professor James Timmons argued this regimen helps increase the effectiveness of insulin by 30%. Timmons may well keep fit by running to avoid angry mobs of soon-to-be redundant personal trainers.

Could three minutes' weekly exercise be enough? Perhaps: vigorous bursts of physical activity kill your appetite, whereas longer workouts can leave you wanting to eat more. Timmons was sceptical about government guidelines recommending 150 minutes moderate and 75 minutes vigorous activity a week: "They're not personalised. People respond very differently to the same exercises." Mosley turned out through Timmons's genetic tests to be a non-responder: his aerobic capacity cannot be increased, even if he works his moneymaker incessantly. Again, not unusual: 20% of us experience negligible benefit from exercise; 15% experience a huge benefit from aerobic workouts.

As for food, Mosley argued that 95% of diets fail partly because the body conspires against the will. As you lose weight, your metabolic rate slows and your body responds by reducing movement to conserve calories. This isn't what hunky Dr Christian tells patients at his feeding clinic in the new series of Supersize v Superskinny (Channel 4) as he gets them to swap their grotesque diets. I watched this on a diet of custard creams and tears, alternately gorging and sobbing as 25st 1lb Helen and 6st 5lbs Catherine bonded. "If we carry on as we are we're gonna be dead in 10 years. Right, babe?" "Yeah, babe."

Christian took his centre parting to America's fat capital, Evansville, Indiana, where one third of citizens are obese. At the the local hospital he met 55-year-old Nancy, whose ankle is deformed because of diabetes. She also lost a toe because of a diabetic ulcer. Is Britain turning into Evansville? It is, Christian argued, more than possible.

You can sit down now.