Why it’s so hard to shed the fat

Diets rarely work – not in the long term, says Jenni Russell. And there’s a scientific reason for this. “Our bodies like equilibrium and they establish set points to which they want to return.” Put a few extra pounds on over Christmas and it’s relatively easy to lose them; remain overweight for a long time – “no one is quite sure how long; perhaps a year” – and you effectively reset your default weight at this higher level.

When you then try to shed that fat, your body fights to retain the extra reserves by increasing the level of your hunger hormones and slowing down your metabolism. So a newly thin person will always have to eat less, or exercise more, than someone who has simply maintained that weight.

The lesson is clear: unless we want rising obesity levels to bankrupt the NHS, we must devote our energies to preventing people, children in particular, from getting fat in the first place. US studies show that 80% of obese children become obese adults, whereas less than 5% of normal-sized children do. In the long run, this is a far more important issue “than HS2, or where to put a third runway”.