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Dieting Doesn’t Work Because Your Brain Limits Fat Burning

Your brain doesn’t let you burn fat when you’re dieting because it is protecting you from a scarcity of food by preventing you from getting rid of those calories! Or so suggests a new study published in eLife.

Losing weight is no easy task, and many will attest to the fact that dieting will, sometimes, prove to be inefficient. Why does this happen? New research conducted by scientists from the University of Cambridge attempts to solve the puzzling question: apparently, certain brain cells prevent the burning of calories during dieting because they ‘think’ that food is scarce.

Study lead author Dr Clémence Blouet explains that the body tends to balance the amount of calories burnt, and the amount consumed, a system acting like a caloric thermostat. Therefore, when someone is eating less than he normally does, his body will compensate for this change by burning fewer calories. Therefore, losing weight gets even harder. Now, how does the brain beat you at your own game?!

The research team was able to identify the mechanism that brings about this adaptation in mice, an animal considered a useful model for humans because of their biological and physiological resemblance.

A specific group of neurones found in the hypothalamus, called agouti-related neuropeptide (AGRP), believed to play a role in appetite regulation, were analysed. Activated AGRP neurones cause us to eat while, when inhibited completely, they might result in anorexia. The researchers manipulated this ‘switch’ genetically, turning the AGRP neurones on and off, to control their activity. All the while, the mice’s energy expenditure and temperature were measured as the availability of food was varied.

The findings show that AGRP neurones are crucial to the functioning of the caloric thermostat regulating the quantity of calories burnt, and thus controlling weight as well. Even if the neurones cause us to eat when they are activated, they play a different role when no food is available: they, instead, act to save energy, thereby restricting the number of calories to be burnt, resulting in a limited weight loss. Then, when food is available again (that is, when the person starts eating), everything goes back to normal, and energy expenditure is restored to its usual figures.

“Our 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’s available in the environment,” says Dr Blouet. “If food is available, they make us eat, and if food is scarce, they turn our body into saving mode and stop us from burning fat.”

Dr Blouet adds that this ability might have evolved to serve as a coping mechanism for famine. In our contemporary world, this type of famine situation would be dieting, and the brain sets in motion the AGRP neurone activity as required. This would explain why dieting does not lead to the wanted results for some people.

Good news, this study might help counter the problem of ineffective weight loss strategies.

“This study could help in the design of new or improved therapies in future to help reduce overeating and obesity. Until then, 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,” says co-author Dr Luke Burke.


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