Updated: Dec 20, 2020
Are you puzzled by the seemingly endless promotion of weight loss strategies and diets? In this series, we look at some popular diets - and the research behind them.
Healthy weight loss What are they?
The ketogenic or "keto" diet is a low-carbohydrate, high-fat diet that has been used for centuries to treat certain diseases. In the 19th century, the ketogenic diet was often used to control diabetes. In 1920, it was introduced as an effective treatment for epilepsy in children for whom drugs were ineffective. The ketogenic diet was also tested for cancer, diabetes, polycystic ovary syndrome and Alzheimer's disease and was used in closely monitored areas.
However, the diet is receiving considerable attention as a potential weight loss strategy due to the low carbohydrate diet craze that began in the 1970s with the Atkins diet (a very low carbohydrate, high protein diet that was commercially successful and took low carbohydrate diets to a new level of popularity). Today, other low carbohydrate diets such as the Paleo, South Beach and Dukan diets are all high in protein but moderate in fat. The ketogenic diet, on the other hand, is characterised by its exceptionally high fat content, generally between 70 and 80%, but with a moderate protein intake.
How does it work?
The ketogenic diet is based on the principle that when glucose - the main source of energy for all cells in the body, which is obtained by eating carbohydrate foods - is eliminated from the body, an alternative fuel, called ketones, is produced from the stored fat (hence the term "keto" - genetically determined). The brain needs glucose the most, about 120 grams a day, if it is supplied uniformly, because it cannot store glucose. During fasting or when very little carbohydrate is consumed, the body first draws the stored glucose from the liver and temporarily breaks down the muscles to release the glucose. If this continues for 3-4 days and the stored glucose is completely depleted, blood levels of a hormone called insulin drop and the body begins to use fat as its main fuel. The liver produces ketones from fat, which can be used in the absence of glucose. 
When ketone bodies accumulate in the blood, this is called ketosis. Healthy people naturally suffer from slight ketosis during periods of fasting (e.g. during the night) and during very intense exercise. Proponents of the ketogenic diet argue that if the diet is followed carefully, blood levels of ketones should not reach a harmful level (known as "ketoacidosis") because the brain uses ketones as fuel and healthy people usually produce enough insulin to prevent the formation of too many ketones. 2] The speed at which ketosis occurs and the number of ketones accumulated in the blood varies from person to person and depends on factors such as body fat percentage and resting metabolic rate. 
An excess of ketone bodies can produce a dangerously toxic level of acid in the blood, called ketoacidosis. During ketoacidosis, the kidneys begin to excrete ketones in the urine along with body water, causing fluid-related weight loss. Ketoacidosis is more common in people with type 1 diabetes because they do not produce insulin, a hormone that prevents the overproduction of ketones. In a few rare cases, however, ketoacidosis has been reported in non-diabetics after a long and very low-carbohydrate diet. [4,5]
There is no single "standard ketogenic" diet with a certain ratio of macronutrients (carbohydrates, proteins, fats). The ketogenic diet generally reduces total carbohydrate intake to less than 50 grams per day - less than the amount contained in an average bagel - and can be as much as 20 grams per day. In general, common ketogenic resources assume an average fat content of 70-80% of total daily calories, 5-10% carbohydrate and 10-20% protein. For a 2000 calorie diet, this corresponds to about 165 grams of fat, 40 grams of carbohydrates and 75 grams of protein. The amount of protein in the ketogenic diet is moderated by