Virtually all weight loss diets to varying degrees focus on either calorie reduction or the manipulation of the intake of one of the three essential macronutrients (proteins, fats, or carbohydrates) to achieve their weight loss effects.
Ketogenic diets are a group of "high-fat, moderate protein" or "high-protein moderate fat" but very low-carbohydrate diets. The term ketogenic basically refers to the increased production of ketone bodies occasioned by the elevated rate of lipolysis (fat break down). Ketones are the acidic by-products formed during the intermediate break down of "fat" into "fatty acids" by the liver.
The first sets of effective ketogenic diet were actually developed as far back as the early 1920s by the Johns Hopkins Pediatric Epilepsy Center and also by Dr. R.M. Wilder of the Mayo Clinic to treat children with hard to control seizures. The diets were designed to mimic the biochemical changes that occurred during periods of fasting, namely ketosis, acidosis, and dehydration. The diets involved the consumption of about 10-15 grams of carbohydrates per day, 1 gram of protein per kilogram bodyweight of the patient and the remaining calories derived from fats.
Today, the promoters of ketogenic diets are strongly of the view that carbohydrates especially the high glycemic index ones are the major reasons why people gain weight. Carbohydrate foods are generally metabolized to produce glucose, a form of simple sugar that is generally regarded as the preferred energy source for the body as it is a faster burning energy. Although the body can break down muscle glycogen (a mixture of glucose and water) and fat to produce energy, it however prefers to get it from high glycemic index carbohydrates from diets.
Of the macronutrients, carbohydrates are therefore argued to be the major cause of weight gain. This is more so because the increased intake of high glycemic index carbohydrate foods generally causes fluctuating blood sugar levels due to their fast absorption into the bloodstream and which more often than not leads to the overproduction of insulin. This is where the problem actually starts.
Insulin is a hormone that regulates blood glucose levels and therefore maintenance of the energy in/energy out equation of the body which rules body weight. Excess amounts of glucose in the bloodstream causes the excessive secretion of insulin which leads to the storage of the excess glucose in the body as either glycogen in liver and muscle cells or fat in fat cells.
One aim of ketogenic diets is therefore to reduce insulin production to its barest minimum by drastically reducing carbohydrate consumption while using fats and proteins to supplement the body's energy requirement.