Do we need carbohydrates to live?

The food we eat has three macronutrients – carbohydrates, fat, and protein – plus some micronutrients like vitamins and minerals. A lot of the energy goes to power our large mammalian brains. We estimate that the brain needs 130g of glucose, the end product of all carbohydrates, per day. We also draw the line for a low carbohydrate diet at this amount.

Many people believe that we need carbohydrates in our diet for the brain to work right. We’re smarter than that. In the absence of carbohydrates, the brain turns to ketone bodies for fuel. For this reason, we store energy as fat, so that during periods of fasting the body still receives the energy it needs to maintain homeostasis. A small part of the brain indeed remains glucose-dependent, but it can derive energy from gluconeogenesis – the process where protein becomes glucose. Both protein and fat are essential nutrients. Carbohydrates are not. Many advocates of low-carb diets like to point back to our ancestral diet before we got agriculture 10,000 years ago.

The state where the body burns ketone bodies derived from fat rather than glucose is called ketosis. I find that I stay in ketosis when I eat less than 50g of carbohydrates per day. There’s a lot of hype around ketosis as a magic bullet for weight loss. I’ve both gained and lost weight in the past year and a half that I’ve spent in ketosis. For me, the amount of calories, specifically how much butter and cheese I eat, is the determining factor. Not ketosis in itself.

It’s worth noting that many overweight type 2 diabetics, when they combine the ketogenic diet with intermittent fasting, lose weight. It probably is due to eating less as well as lowering insulin levels. Insulin is a storage hormone, so burning off fat when you’re suffering from hyperinsulinemia is difficult.

Finally, ketosis is not the same as ketoacidosis. Some medical professionals confuse the two and are terrified of ketosis in their patients with type 1 diabetes as a result. In ketoacidosis, the body is wasting itself with high blood sugar, ketones, and a shift in the acid-base balance of the blood. It’s a medical emergency. In nutritional ketosis, you see low levels of ketones as the body has adapted to burning fat but blood sugar remains normal. While both involve ketones, they’re two completely different states.

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