New Study Reveals Why Extreme Calorie-Restriction Diets Just Don't Work

A new study reveals how extreme calorie-restriction diets trick our bodies into "survival mode" and prevent us from burning fat.

On the surface, extreme calorie-restriction diets seem like a surefire way to lose weight.

By restricting your calories to less than 1,200 or so per day, you're almost guaranteed to create a massive caloric deficit—i.e., you'll burn more calories than you consume on a daily basis. However, our bodies aren't quite that simple.

As it turns out, our brains often prevent us from burning calories in such situations as a means of survival. A new study published in the journal eLife shines light on this phenomenon. The study—which was carried out in mice—found that certain brain cells may prevent us from burning calories when our bodies believe food is scarce. Science Daily explains the methods used in the study:

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.

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. They studied the mice in special chambers than 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.

Researchers found that these neurons are capable of "flipping a switch" that dictates whether our bodies go into calorie-burning mode or calorie-saving mode. If they believe food is widely available, they entice us to eat. If they believe food is scarce, they go into survival mode and stop us from burning fat.

"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. Clémence Blouet, who led the study. "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."

Our bodies didn't evolve with dieting in mind. Dieting, in the modern sense, has only existed for a fraction of human history. Our great ancestors ate for survival, not for aesthetics. If they were in a significant caloric deficit, it's not because they wanted to shed some pounds before beach season—it's because they simply didn't have enough food. Our bodies are still designed to defend against these situations, which makes extreme calorie-restriction diets counterintuitive. If you go on one, you're likely going to be making a lot of sacrifice for minimal results.

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

By keeping the reduction in caloric intake moderate as opposed to extreme, you're putting yourself in a better biological position to see sustainable results.

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