Trying to lose weight? Dieting may not help

Dieting has a little effect on losing weight, as a study finds that brain cells act as a trigger to prevent us burning calories when food is scarce.

The findings suggest that a group of neurons in the brain coordinate appetite and energy expenditure and can turn a switch on and off to burn or spare calories depending on what is available in the environment.

According to researchers from the University of Cambridge, if food is available then the neurons make us eat and if food is scarce then they turn our body into saving mode and stop us from burning fat.

They 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.

"Weight loss strategies are often inefficient because the body works like a thermostat and couples the amount of calories we burn to the amount of calories we eat," said lead study author Dr Clemence Blouet.

"When we eat less, our body compensates and burns fewer calories, which makes losing weight harder. We know that the brain must regulate this caloric thermostat, but how it adjusts calorie burning to the amount of food we've eaten has been something of a mystery," Blouet

added.

Now, in research published in the open access journal eLife.

The team 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.

The researchers 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 no food is 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.