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The most basic premise of the ketogenic diet is that the body can be forced to burn greater amounts of fat by decreasing its use of glucose.
The primary determinant of fuel utilization in humans is carbohydrate availability, which affects hormone levels. Additional factors affecting fuel utilization are the status of liver glycogen (full or empty) as well as the levels of certain enzymes.
The fact that the brain is incapable of using FFA for fuel has led to one of the biggest misconceptions about human physiology: that the brain can only use glucose for fuel. While it is true that the brain normally runs on glucose, the brain will readily use ketones for fuel if they are available.
Under normal dietary conditions, ketone concentrations are so low that ketones provide a negligible amount of energy to the tissues of the body. If ketone concentrations increase, most tissues in the body will begin to derive some portion of their energy requirements from ketones.
When carbohydrate availability is high, carbohydrate use and storage is high and fat use is low. When carbohydrate availability is low, carbohydrate use and storage is low and fat use is high.
When blood glucose increases, insulin levels increase as well, causing glucose in the bloodstream to be stored as glycogen in the muscle or liver. Excess glucose can be pushed into fat cells for storage.
The liver is always producing ketones to some small degree and they are always present in the bloodstream. Under normal dietary conditions, ketone concentrations are simply too low to be of any physiological consequence. A ketogenic diet increases the amount of ketones which are produced and the blood concentrations seen.
The major difference between starvation, dietary and diabetic/alcoholic ketoacidosis is in the level of ketone concentrations seen in the blood. Starvation and dietary ketosis will normally not progress to dangerous levels, due to various feedback loops which are present in the body. Diabetic and alcoholic ketoacidosis are both potentially fatal conditions.
The general metabolic state of ketosis can be further subdivided into two categories. The first is ketonemia which describes the buildup of ketone bodies in the bloodstream. The second subdivision is ketonuria which describes the buildup and excretion of ketone bodies in the urine, which occurs due to the accumulation of ketones in the kidney.
Most tissues except the brain, stop using ketones for fuel after the third week of ketosis. This is especially true for skeletal muscle. While muscle initially derives up to 50% of its energy requirements from ketones, this drops to 4-6% by the third week of ketosis.
During the first few days of ketosis, the brain is incapable of using ketones for fuel. By using a large amount of ketones for fuel, skeletal muscle prevents a rapid increase in blood ketone levels, which might cause acidosis. As time passes and the brain adapts to using ketones for fuel, skeletal muscle must stop using ketones for fuel, to avoid depriving the brain of fuel.
When carbohydrate is removed from the diet, the body undergoes at least three major adaptations to conserve what little glucose and protein it does have. The primary adaptation is an overall shift in fuel utilization from glucose to FFA in most tissues. This shift spares what little glucose is available to fuel the brain.
The initial storage depot of carbohydrate in the body is the liver, which contains enough glycogen to sustain the brain’s glucose needs for approximately 12-16 hours.
The loss of body protein during total starvation is unacceptable but the [...] body goes through a series of adaptations to conserve its protein. [...] the addition of dietary protein will maintain ketosis, while preventing the breakdown of bodily protein. In brief, rather than break down bodily protein to produce glucose, the body will use some of the incoming dietary protein for glucose production.
After much research, it was concluded that a protein intake of 1.5-1.75 grams protein per kilogram of ideal body weight would spare most of the nitrogen loss, especially as ketosis developed and the body’s glucose requirements decreased.
Carbohydrate is 100% anti-ketogenic. Protein is approximately 46% ketogenic and 58% anti-ketogenic. Fat is 90% ketogenic and 10% anti-ketogenic.
A well established fact is that low-carbohydrate diets tend to cause a rapid loss of water in the first few days. This occurs [because] glycogen is stored along with water in a ratio of three grams of water for every gram of stored carbohydrate. As glycogen is depleted, water is lost.
A popular belief states that fat can be lost on a ketogenic diet without the creation of a caloric deficit. Most individuals will automatically reduce their caloric intake when they restrict carbohydrate to low levels. Therefore, in a sense individuals are losing weight eating ‘as much as they like’, it is simply that they are eating less than they think.
To avoid metabolic slowdown from an excessively low caloric intake, dietary fat is necessary as a caloric ballast since protein and carbohydrates must be kept relatively static on a ketogenic diet.
1. Improve the nutrient quality of the low carb week
2. Eat the day’s calories across fewer meals
3. Take a week off the diet
4. Cycle calories throughout the week
The main problem with the scale is that it does not differentiate between what is being gained or lost (i.e. muscle, fat, water). Ideally the scale should always be used along with skinfold measurements or the tape measure for more accurate measures of changes in body composition.
Whether correct or not, many ketogenic dieters tend to live or die by the presence of ketones in their urine. The presence of ketosis, which is indicative of lipolysis can be psychologically reassuring [...]. However it should be noted that one can be in ketosis, defined as ketones in the bloodstream, without showing urinary ketones.
When muscle glycogen falls to extremely low levels (about 40 mmol/kg), anaerobic exercise performance may be negatively affected. Individuals following a ketogenic diet who wish to lift weights or perform sprint training must make modifications by consuming carbohydrates for optimal performance.
Any calorically restricted diet may not provide for all nutritional requirements and the limited number of food available on a ketogenic diet may cause deficiencies [...]. At the very least, individuals on a ketogenic diet should take some form of sugar free vitamin and mineral supplement to ensure nutritional adequacy.
Originally compiled by LadySixString.