Will a Low-Carb Diet Really Boost Your Metabolism?

According to Google Search data, interest in the ketogenic diet appears to have waned significantly lately. But the popular and scientific fascination with low-carb diets persists.

The ketogenic diet, of course, is just the latest reincarnation of other diets that severely restrict carbohydrates, including the Atkins, South Beach, and Dukan diets. The goal of these very-low-carb diets is to induce ketosis, where the body’s cells are forced to burn fat for energy instead of sugar. 

Just because the body is using fat as its fuel source, that doesn’t necessarily mean it’s burning body fat.

Although sugar (or carbohydrate) is the body’s preferred source of energy, we have very flexible metabolisms. If sugar isn’t available and fat is, the body can switch over to burn fat instead. Sort of like a car that can run on both gas and electric power. If the battery runs out of juice, the car can burn gasoline until you have a chance to recharge your batteries.

RELATED: Carbs or Fat: Which Is the Body's Preferred Fuel Source?

Just because the body is using fat as its fuel source, that doesn’t necessarily mean it’s burning body fat. First, it will be burning the fat that you eat, and ketogenic diets tend to be very high in fat. You'll only start burning body fat for energy when your body runs out of dietary fuel. So if you take in fewer calories than you burn, your body will turn to its fat stores to make up the difference. But this is true of any diet, not just low-carb diets.

So why the continuing fascination with very-low-carb diets? Well, one advantage of being in ketosis for a prolonged period of time is that it suppresses your appetite. That can make it easier to eat less. But in order to reap this advantage, you have to be pretty strict in your avoidance of carbohydrates.

What is the carbohydrate-insulin hypothesis?

Very-low-carb diets also tend to reduce blood sugar levels and insulin production. One of the normal (and necessary) biological functions of insulin is to promote fat storage. The carbohydrate-insulin hypothesis supposes that a diet high in carbs would result in higher insulin levels, which would, in turn, cause you to store fat and become obese. Restricting carbohydrates, therefore, should suppress insulin, trigger fat burning, and reverse obesity.

Study after study, including some designed and funded by proponents of the carbohydrate-insulin theory, have failed to prove the theory.

The carbohydrate-insulin theory also argues that low-carb diets lead to weight loss because they increase your metabolism, or the number of calories you burn. Theoretically, you would lose more weight...

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