Introduction
A “diet” refers to the collection of food and drinks regularly consumed by an individual, which forms a part of their lifestyle. It also means a restricted or selective intake of food to achieve a set objective, be it for improving one’s stamina, immunity, health, or even to lose weight.
People follow different types of diets, depending on what factors influence their choice of food. These range from physiological and health-related factors, to cultural and religious limitations. Dietary types such as plant-based, vegan, mediterranean, low-carb, ultra-low-fat, intermittent fasting, ketogenic diet, etc., each have their specific characteristics and benefits.
People, while choosing their diet, turn to various sources for information and a sample diet plan. While such information and advice is abundant, it also becomes important for one to understand the choice they make, along with the benefits and side effects that accompany such a choice.
Ketosis - a physiological overview
The rationale behind adopting a keto diet lies in its physiological processes and effects. A simplified understanding of the same will provide a better insight into what appears to be an anomaly to the stereotypical notion of “dieting”.
The human body primarily uses glucose as its fuel to function. Since ketosis means a drastic reduction in carbohydrate intake, it will result in the depletion of the body’s go-to energy source: glucose. Such low levels of glucose being insufficient to act as a source of energy, the body is prompted to switch to an alternative source. It then turns to the free fatty acids released by fat cells. These are sent to the liver, where they undergo several biochemical reactions to produce ketone bodies.
Ketone bodies are a result of beta-oxidation of fatty acids and can be utilised by every cell in the body as a powerful source of energy to meet their functional requirements.
This process occurs over two stages:
Ketogenesis: The production of ketone bodies takes place in the liver, where fatty acids are broken down into Acetyl coenzyme A (“acetyl CoA”) along with the release of Acetoacetate (“AcAc”), which is one of the three ketone bodies. The other two: Acetone and Beta-Hydroxybutyrate (“BHB”) are derived from AcAc. Acetone is produced through spontaneous degradation of AcAc and is excreted through breath and sweat. On the other hand, BHB is the product of a reaction that AcAc undergoes with the enzyme BHB-dehydrogenase. BHB is then transported out of the liver through monocarboxylate transporters making its way into the bloodstream. BHB occurs in two forms: dextro and levo (a detailed explanation is given below).
Ketolysis: Although the liver is the genesis of ketone bodies, it lacks the ability to convert them into energy, which requires the production of adenosine triphosphate (“ATP”). BHB is converted and used as energy in the brain and the muscles. BHB is converted back into AcAc through a reversible reaction with BHB dehydrogenase, and then into acetyl CoA. This enters the Krebs cycle, ultimately producing ATP, which is used as energy by the cells.
BHB level in the blood is abundant (~80% of ketone bodies), making it easier to be circulated. This is also the reason for them being used to measuring blood ketone levels. Unlike fatty acids, it is relatively easier for BHB to cross the blood-brain barrier. This enables the ketone bodies to be utilised by the brain for its cognitive functioning. The oxidation of fatty acids would have led to an oxygen-poor environment for neurons as the process would consume a large amount of oxygen. This would also be slow, impairing the brain’s ability to take quick decisions, commonly termed “brain fog”.
