So far on this blog, I’ve discussed metabolism of the three primary macronutrients within the body and their metabolism under normal conditions, but sometimes they’re used a little bit differently if circumstances aren’t normal. An example of this would be a Ketogenic diet, which is a type of high fat, very low carbohydrate diet that induces a state of nutritional ketosis.

Nutritional Ketosis

Nutritional Ketosis is a state in which the body begins to metabolise fats into ketone bodies. It does this because the brain needs energy to function which is usually provided for by glucose, but if we reduce carbohydrates, we have less glucose available to us. The body is smart, it doesn’t want us to be at risk of having no energy for our brain if we can’t get access to carbohydrates, and this is where Ketone bodies come in.

Fatty acids cannot pass the blood-brain barrier and, therefore, cannot be used for brain fuel. But, fatty acids can be broken down into very high energy intermediates called ketone bodies which can spare some of the glucose requirement in the brain. The term ketone bodies (KBs) refers to three molecules: Acetoacetate (AcAc), 3-hydroxybutyrate (3HB) and acetone. Seen below.

Ketone bodies go through the blood-brain barrier to be used for energy. In fact, the Ketone bodies are such good sources of energy they outperform glucose in the brain, the central Ketone body, beta-hydroxybutyrate can produce 8.7kg of ATP per 100g, and glucose only produces 6.9kg of ATP for the same amount. As we know from my earlier post on energy metabolism, ATP is the universal energy for all of our cells.

We will enter this ketogenic state under conditions of starvation as well as very low carbohydrate consumption, which had led to the theory that this is a metabolic pathway that was implicated in our ancestor’s survival when they had very limited carbs or were under conditions of famine. The people that had this metabolic advantage to survive without needing as much glucose would have passed this on to us.

Ketogenic diets

An earlier post discussed the metabolism of Ketogenic diets, but here is just a quick outline of what they are. A ketogenic diet is an extremely low carbohydrate diet, so low that the body begins to produce something called Ketone bodies. The idea is that the body will start to use more fat as energy and thus lead to greater weight loss.

The science. A 2008 study on Obese people allowed them to eat a Ketogenic diet ad libitum; that meant they could eat as much fat as they liked as long as they controlled their protein and carbs. The study found that the diet reduced hunger, and the participants reduced their calorie intake by choice, which led to much greater weight loss! Ketogenic diets may even have some therapeutic uses!

The takeaway – There’s a pathway that exists in metabolism to save us from starving to death if we don’t have any carbs. Which is great if you’re an Eskimo.


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