Waistband feeling a bit tighter, or buttons straining after Christmas?
While it’s easy to blame your appalling willpower or TV-inspired lethargy, according to a respected U.S. obesity expert, weight gain might not be your fault at all.
In a fascinating new book, Robert Lustig, a professor of clinical paediatrics at the University of California, expounds a whole new scientific theory.
He 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 Lustig warns that our sweet tooth is sending this process haywire.
SUGAR TRICKS YOUR BRAIN
For many years scientists thought obesity could be caused by a shortage of leptin — thinking that without adequate levels, overweight people simply never received the message that they were full.
But more recent studies have shown that obese people have plenty of leptin (in fact, the fatter you are, the more of it you appear to have), but are more likely to be ‘leptin-resistant’.
This means the cells in the brain that should register leptin no longer ‘read’ the signals saying the body is full, but instead assume it is starving — no matter how much food you continue to eat.
In panic, the brain pumps out instructions to increase energy storage — instigating powerful cravings for high-fat, high-sugar foods because these are the easiest and most immediate forms of energy — and conserve energy usage, by dampening any urge to get up off the sofa and go for a run.
The food cravings are made even more intense — and impossible to resist — because leptin is supposed to dampen the feeling of pleasure and enjoyment you get from food by suppressing the release of the brain chemical dopamine, helping to decrease appetite.
But if you are leptin-resistant, food never stops tasting delicious, no matter how much of it you eat.
This, says Professor Lustig, is why many overweight people find it so hard to stop eating, and why diets so often fail.