a professor of clinical pediatrics at the University of California...argues that the urge to overeat and lounge around doing nothing is not a sign of weakness.

It is, he says, a hormonal issue, triggered by eating too much sugar.

He points the finger of blame at the hormone leptin, which acts like an appetite thermostat.

As one of two ‘hunger hormones’ in the body, leptin works to decrease the appetite (its partner, ghrelin, increases appetite).

When you have had enough to eat, your fat cells release leptin, which effectively dulls the appetite by instructing the brain that it’s time to stop eating.

But Professor [Robert] Lustig warns that our sweet tooth is sending this process haywire...

...Professor Lustig believes the key to losing weight is to reverse leptin resistance. Here is his action plan:

Have just one dessert a week

When cooking, reduce sugar in every recipe by a third, and eat dessert as a treat, once a week.

Fiber leads to weight loss

Fiber is now routinely stripped from foods to give a finer texture and extend shelf life (manufacturers have found food with fiber doesn’t freeze well, and can’t be cooked quickly), but according to Professor Lustig: ‘Fiber, or roughage, is the most misunderstood weapon in our nutritional arsenal.’

This is because the digestive system has to work to strip away the outside bran of a wholegrain, so slowing the whole digestive process, and stopping glucose levels from peaking suddenly.

This means less insulin is released, therefore less energy is stored as fat. Slower digestion also gives your brain a chance to register that you are full.

Take 15 minutes’ exercise daily

Exercise alone cannot cause significant weight loss (unless you change your diet at the same time) but Professor Lustig says 15 minutes a day is enough to improve your insulin sensitivity (because activity helps cells become more receptive to insulin), and build muscle at the expense of fat.

Although you may not see a drop on the scales, by improving insulin sensitivity and lowering insulin levels, exercise, will improve leptin signalling.

Eat like your Grandma

Beware packaged food. Professor Lustig’s mantra is: ‘Don’t eat anything your grandmother wouldn’t recognize. If the food has a company logo you’ve heard of, it’s processed.’

Don’t eat on your feet

Eating standing up means you will be eating fast, with no time for satiety signals to kick in, says Professor Lustig.

Always include some sort of protein (chicken, pulses) in every meal (to slow the digestive process and reduce the risk of insulin spikes) and avoid any ‘food’ that is just fat, carbohydrate and sugar (such as doughnuts, milk-shakes, pastries).