How does the Keto Diet Work?
To preface this section: I am not a licensed nutritionist, nor did I major in Bio/Organic chemistry, so some of my verbiage here may be off. Bear with me, though — I will aim to be as precise as possible.
For the nutritionally uninitiated, common-knowledge nutritional science dictates that the human body needs 3 main macronutrients to survive: Fats, Carbohydrates, and Proteins, all of which have a corresponding calorie count when metabolized fully in the body (4 kcal/g for Carbs, 9kcal/g for Fats, and 4 kcal/g for Proteins). A “complete diet” for a human will involve some proportion of these 3 macronutrients, or macros — for example, if a bodybuilder is aiming to put on mass and must eat around 3000 calories a day to do so, it will be critical that a high proportion (30–45%, depending on who you ask) of these calories come from protein. This proportion will vary widely depending on one’s fitness regime, daily activity level, body composition, general state of health, and genetic profile (no two humans are alike and there is no universal dietary “catch-all”), but close attention should always be paid to macronutrient split when putting together a complete, holistic meal plan.
Each macronutrient has different functions throughout the body: Carbs serve as energy sources while also helping with digestion, Fats help maintain joint, brain, and organ health, and proteins help build and maintain muscle mass — and, of course, each macronutrient has many more uses throughout the body, but this is just a snapshot.
As such, traditional nutritional wisdom has held that Carbohydrates are — and should rightfully be — the main source of energy in the human diet. While the body is physically able to metabolize all 3 macronutrients into energy (an evolutionary adaptation which has allowed humans to survive even with little access to food), the metabolic process for metabolizing carbohydrates is the most effective & efficient — it is, if I may borrow some technical language, effectively the “default” metabolic setting for the body, with processes for the other 2 macronutrients being often delegated to secondary status. And while nutritional science is a relatively recent addition to the scientific lexicon, this conclusion has still been historically easy to accept, given that the lion’s share of readily-farmable food crops on planet earth have been Carbohydrate-rich: wheat, grain, corn, rice, potatoes, quinoa, most fruits, beetroot, etc.
This is where the Ketogenic diet disagrees. The Keto diet hypothesizes that the process for metabolizing fats for energy — Ketosis, from which the diet gets its name — is an equally effective way for the body to receive all of its energy. The Keto diet also supposes that the reasons that carbohydrates have historically held such prominence in the human diet are more external than anything else; i.e. mainly due to their abundance on Earth and the ease with which they are farmed. As such, the central idea of the Keto diet is to force the body to metabolize fats as the primary source of energy in the same way that it would do for carbohydrates.
This comes back to evolution and adaptation. If we view the human body as a state machine — i.e. a machine with several defined “states” triggered by different external stimuli — the primary state would be one of metabolizing carbohydrates for energy. In this state, the body will use all 3 macronutrients for their various processes, but will rely on carbohydrates as its main source of energy for both muscles and vital organs. As such, if the body in this state does not receive enough carbohydrates, feelings such as drowsiness, dizziness, irritability or lack of focus may occur — the body’s way of telling you that it needs to eat. Additionally, if the body in this state receives too many carbohydrates (i.e. more than it needs to power muscles through their daily physical regimen, a threshold which also depends on a variety of factors), then the remaining nutrients will be stored in the form of body fat, to be metabolized at a later date when carbohydrates are scarce. This state can be likened to the kind of “default” state that I referenced above.
However, what happens when the body doesn’t receive enough carbohydrates for a lengthy-enough period of time? This would be our next state: Ketosis. Ketosis is the process by which fatty acids — either from food or from body fat cells — are broken down in the liver into one of three bodies known as Ketone Bodies, which can then be used as an energy source in various places throughout the body, primarily in the brain. The body will typically enter Ketosis after 3 or more days without Carbohydrates, though this number, again, will vary slightly person-to-person. Ketosis is, thus, essentially an anti-starvation adaptation; it is the human body’s way of ensuring that, by turning to fat stores for energy, the body will still be able to run even after food has become unavailable for an extended period of time.
This is the central idea behind the Keto diet: enter Ketosis by severely limiting Carbohydrate intake, effectively forcing the body to burn fat in order to maintain muscles and vital organs. As such, the Keto diet is highly effective at burning off excess body fat. While the diet has a number of different effects on the body, one thing is certain: The Keto diet is highly effective at burning fat.