Weight loss sends ‘red flag’ to brain, researcher warns

Dieting is hard because weight loss sets off an evolutionary “red flag” in the brain which triggers hunger cravings, a Cambridge University geneticist has warned.

Giles Yeo told last month’s Hay Festival in Hay-On-Wye, U.K., that losing weight is meant to be difficult because humans are hardwired to maintain a constant size for the best chance of survival.

Some people find it harder to diet because their genes cause their brain to underestimate body weight from signals released by fat cells, causing the body to make hunger hormones.

“Losing weight ain’t easy, and it isn’t meant to be,” said Yeo, author of Gene Eating. “It doesn’t matter how skinny you are, your brain perceives weight-loss as a big red flag, a decrease in your chances of survival.

“The moment you lose weight your brain ... drags you kicking and screaming back up to the weight you were.”

Yeo said the only way to lose weight is to follow the first law of thermodynamics: energy cannot be created or destroyed. People must eat more than they burn to gain weight, and burn more than they eat to lose weight.

“It’s physics,” he said. “Anyone who is selling you an effortless way to lose weight is lying.”

No foods should be off limits, Yeo said, unless there is a clinical reason not to eat them. Gluten or milk were fine for 95 per cent of white Europeans. Whereas most mammals do not consume milk after childhood, humans developed a mutation, after the birth of agriculture and animal domestication about 7,500 years ago, that allowed the digestion of lactose in adulthood.

Instead of cutting out food groups, he suggested eating a little of everything.

“Moderating is intensively boring, and it’s very difficult,” he said. “People have removed all kinds of stuff from their diet ... They are now naming things gluten-free which never had gluten to begin with.”

He advised dieters to stop counting calories because with many foods all the calories are not absorbed. People absorb only about 70 per cent of the calories in meat, which is why diets that cut out carbohydrates are effective. Similarly vegan diets work because plants are bulky, Yeo said.

“The caloric availability from vegan food is lower than everything else. In 29 days on a vegan diet I lost 10 pounds while eating as much as I wanted and my blood cholesterol dropped 12 per cent.

“Except let’s look at why. A plant-based diet is very bulky. So what actually happened is I ended up eating less calories. My cholesterol level dropped because I lost weight but largely because I gave up saturated fats.”