The Truth About Body Fat

In our weight-obsessed culture, it’s common to disparage the fat in our bodies. But body fat is a highly specialized organ, critically important for health and longevity. Among its many functions, fat surrounds and cushions vital organs like the kidneys and insulates us against the cold. Body fat also signifies health, conferring beauty when distributed in the right amounts and locations. But critically, fat is our fuel tank — a strategic calorie reserve to protect against starvation.

Compared to other species our size, humans have an exceptionally large brain that requires an enormous amount of calories. The metabolic demands of the brain are so great that, under resting conditions, it uses about one of every three calories we consume. And this calorie requirement is absolute. Any interruption would cause immediate loss of consciousness, rapidly followed by seizure, coma, and death. That’s a problem, because until very recently in human history, access to calories had always been unpredictable. Our ancestors faced extended periods of deprivation when a hunt or a staple food crop failed, during harsh winters, or when venturing out across an ocean. The key to their survival was body fat.

If we go for more than a few hours without eating, the body must rely on stored fuels for energy, and these come in three basic types, familiar to anyone who reads a nutrition label: carbohydrate, protein, and fat. The body stores accessible carbohydrate in the liver and protein in muscle, but these are in dilute forms, surrounded by lots of water. In contrast, stored fat is highly concentrated, since fat tissue contains very little water. In addition, pure carbohydrate and protein have less than half the calories of pure fat, making them relatively weak sources of energy. For these reasons, liver and muscle contain only a small fraction of the calories in fat tissue (less than 600 compared to about 3,500 per pound). In the absence of body fat, even a muscular man would waste away in days without eating, whereas all but the leanest adults have enough body fat to survive many weeks.

And these fat cells aren’t just inert storage depots. Fat cells actively take up excess calories soon after meals and release them in a controlled fashion at other times, according to the body’s needs. Fat tissue also responds to and emits a multitude of chemical signals and neural messages, helping fine-tune our metabolism and immune system. But when fat cells malfunction, big problems ensue.

The underlying issue in obesity isn’t having too many calories in the body; it’s not having enough in the right place. High insulin levels — caused by our modern processed diet and other influences — have programmed fat cells to take in and store too many calories, leaving too few for the rest of the body. So we get hungry, and metabolism slows down. Eventually, fat tissue develops chronic inflammation, setting the stage for diabetes and heart disease. Cutting back calories on conventional diets doesn’t solve the fundamental problem: “hungry fat” stuck in calorie storage overdrive. The best way to calm down fat cells is a higher fat diet, with the right balance of protein and natural, slow digesting carbohydrates — which is the basis of the program in my forthcoming book, Always Hungry?

This article originally appeared on Mind Body Green, January 4, 2016.

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