Your brain could stop you from losing weight when on a diet

People who struggle to lose weight by dieting often see no result. And it might be just because their brain is trying to protect them and regulate the ‘caloric thermostat.’

A team of researchers carried out a study in mice and found something that may explain why for some people dieting can be an inefficient way to lose weight.

“The body works like a thermostat and couples the amount of calories we burn to the amount of calories we eat. When we eat less, our body compensates and burns fewer calories, which makes losing weight harder,” Dr Clémence Blouet from the Metabolic Research Laboratories at the University of Cambridge said.

The reason is key brain cells act as a trigger to prevent burning calories when food is scarce. Scientists identified a new mechanism through which the body adapts to low caloric intake and limits weight loss in mice.

According to a University of Cambridge press release, the researchers tested the role of a group of neurons in a brain region known as the hypothalamus. These ‘agouti-related neuropeptide’ (AGRP) neurons are known for their major role in the regulation of appetite: when activated, they make us eat, but when fully inhibited they can lead to almost complete anorexia.

Researchers used a genetic trick to switch the AGRP neurons ‘on’ and ‘off’ in mice so that they could rapidly and reversibly manipulate the neurons’ activity. They studied the mice in special chambers that can measure energy expenditure and implanted them with probes to remotely measure their temperature, a proxy for energy expenditure, in different contexts of food availability.

The team demonstrated that AGRP neurons are key contributors to the caloric thermostat that regulates our weight, regulating how many calories we burn. The findings suggest that when activated, these neurons make us hungry and drive us to eat – but when there is no food available, they act to spare energy, limiting the number of calories that we burn and hence our weight loss.

As soon as food becomes available and we start eating, the action of the AGRP neurons is interrupted and our energy expenditure goes back up again to normal levels.

“While this mechanism may have evolved to help us cope with famine, nowadays most people only encounter such a situation when they are deliberately dieting to lose weight. Our work helps explain why for these people, dieting has little effect on its own over a long period. Our bodies compensate for the reduction in calories,” Dr Blouet explained.

Researchers say the study could help in the design of new or improved therapies in the future to help reduce overeating and obesity. But until then, according to Dr Luke Burke, the study’s first author, the best solution for people to lose weight – at least for those who are only moderately overweight – is a combination of exercise and a moderate reduction in caloric intake.