Ketosis

Ketosis - What is Ketosis?

In biology, ketosis is a state of the organism characterised by elevated levels of ketone bodies in the blood, by the processes of lipolysis and beta-oxidation.

Ketone bodies are formed from excess amount of fat break down. Some of these ketone bodies such as acetoacetate and ß-hydroxybutyrate can also be used for energy.

When glycogen stores are not available in the cells, fat (triacylglycerol) is cleaved to give 3 fatty acid chains and 1 glycerol molecule in a process called lipolysis.

Most of the body is able to utilize fatty acids as an alternative source of energy in a process in which fatty acid chains are cleaved by coenzyme A (CoA) to form acetyl-CoA, which can then be fed into the Krebs cycle.

Acetyl-CoA can only enter the Krebs cycle bound to oxaloacetate. When carbohydrate supplies are inadequate to maintain blood glucose levels, the liver naturally converts oxaloacetate in the liver to glucose via gluconeogenesis for use by the brain and other tissues.

Excess acetyl-CoA in the liver is used to produce ketone bodies, leading to a state of ketosis. During this process, a high concentration of glucagon is present in the serum, which inactivates hexokinase and phosphofructokinase-1 (regulators of glycolysis) indirectly, causing most cells in the body to use fatty acids as their primary energy source.

The brain cannot use fatty acids for energy because the fatty acids cannot cross the blood-brain barrier. However, the ketone bodies produced in the liver can cross the blood-brain barrier. In the brain, these ketone bodies are then incorporated into acetyl-CoA and used in the Krebs cycle.

Excess ketone bodies will slowly decarboxylate into acetone. Acetone is excreted in the breath and urine.

Ketosis should not be confused with ketoacidosis (diabetic ketoacidosis or the less common alcoholic ketoacidosis), which is severe ketosis causing the pH of the blood to drop below 7.2.

Ketoacidosis is a medical condition usually caused by diabetes and accompanied by dehydration, hyperglycemia, ketonuria, and increased levels of glucagon. The high-glucagon, low-insulin serum levels signal the body to produce more glucose via gluconeogenesis and glycogenolysis, and ketone bodies via ketogenesis. High levels of glucose causes the failure of tubular reabsorption in the kidneys, causing water to leak into the tubules in a process called osmotic diuresis, causing dehydration and further exacerbating the acidosis.

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Ketosis Diet

If the diet is changed from a highly glycemic diet to a diet that does not provide sufficient carbohydrate to replenish glycogen stores, the body goes through a set of stages to enter ketosis.

During the initial stages of this process, the adult brain does not burn ketones; however, the brain makes immediate use of this important substrate for lipid synthesis in the brain.

After about 48 hours of this process, the brain starts burning ketones in order to more directly utilize the energy from the fat stores that are being depended upon, and to reserve the glucose only for its absolute needs, thus avoiding the depletion of the body's protein store in the muscles.

Ketosis is deliberately induced in the ketogenic diet used to treat epilepsy. Other uses of low-carbohydrate diets remain controversial.

This article is licensed under the Creative Commons Attribution-ShareAlike License. It uses material from the Wikipedia article on "Ketosis" All material adapted used from Wikipedia is available under the terms of the Creative Commons Attribution-ShareAlike License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.

Ketosis Controversy

Some medical resources regard ketosis as a physiological state associated with chronic starvation.

Some clinicians regard ketosis as a crisis reaction of the body due to a lack of carbohydrates in the diet and consider it a dangerous and potentially life-threatening state that stresses the liver and causes destruction of muscle tissues.

Ketogenesis does not destroy muscle tissue. Ketogenesis can occur solely from the byproduct of fat degradation: acetyl-CoA.

Ketosis, which is accompanied by gluconeogenesis (the creation of de novo glucose from amino acids), is the specific state with which clinicians are concerned.

The anti-ketosis conclusions have been challenged by a number of doctors and adherents of low-carbohydrate diets, who dispute assertions that the body has a preference for glucose and that there are dangers associated with ketosis.

It has been argued that not only did hunter societies live for thousands of years in a primarily ketogenic state, but also that there are many documented cases of modern humans living in these societies for extended periods of time.

While it is believed by some that exercise requires carbohydrate intake in order to replace depleted glycogen stores, studies have shown that after a period of 2–4 weeks adaptation, physical endurance is unaffected by ketosis.

This article is licensed under the Creative Commons Attribution-ShareAlike License. It uses material from the Wikipedia article on "Ketosis" All material adapted used from Wikipedia is available under the terms of the Creative Commons Attribution-ShareAlike License. Wikipedia® itself is a registered trademark of the Wikimedia Foundation, Inc.