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ketosis

 
Dictionary: ke·to·sis   (kē-tō'sĭs) pronunciation
n., pl., -ses (-sēz).
A pathological increase in the production of ketone bodies.

ketotic ke·tot'ic (-tŏt'ĭk) adj.

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World of the Body: ketosis
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Ketosis is recognizable by the smell of acetone (as in nail varnish) on the breath. It occurs when the body's processing of nutrient materials for the release of energy depends predominantly on the use of fats. In the absence of a dietary carbohydrate supply for maintaining blood sugar, or if sugars cannot be utilized normally, fuel must come from stored fat and muscle protein. This can occur in previously healthy people during prolonged fasting or starvation, after persistent vomiting, or on a very high fat and low carbohydrate diet; or it can occur because of disordered hormonal control of metabolism in diabetes mellitus. The high rate of breakdown of fatty acids by the liver produces the ‘ketone bodies’, acetoacetate and b-hydroxybutyrate, which are released into the blood. Some of the acetoacetate is converted to acetone — another ‘ketone body’ — mainly in the lungs, and this becomes noticeable on the breath.

The physiologically useful consequence is that ketone bodies, which are made only in the liver and exported from it, can be used by other tissues for energy production. During starvation even the brain, which normally uses only glucose, can adapt to utilizing ketone bodies.

In diabetes, the fault lies in the absence of the effects of insulin. Normally, this hormone acts to restrain mobilization of amino acids from muscle protein and their conversion to glucose in the liver, and to restrain the mobilization of fatty acids from lipid store in adipose tissue. Without this restraint, the liver not only overloads the blood with glucose, which most other tissues cannot take up and use without the action of insulin, but also overloads the blood with ketone bodies as a by-product of its excessive use of fatty acids. If the condition is uncontrolled — as it used to be before the days of insulin treatment — increasing ketosis leads to progressively more harmful acidosis, diabetic coma, and death.

— Sheila Jennett

See also acid-base homeostasis; fats; insulin; liver.

Food and Nutrition: ketosis
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High concentrations of ketone bodies in the blood.

Excessive ketone formation resulting from fat breakdown and which increases body fluid acidity. See also acidosis.

1. accumulation in the blood and tissues of large quantities of the ketone bodies: β-hydroxybutyric acid, acetoacetic acid and acetone. Because the first two are acids, this results in metabolic acidosis. Thus, the condition is often referred to as ketoacidosis.
2. in ruminants is used synonymously with acetonemia, pregnancy toxemia. See also fat cow syndrome.

  • secondary k. — acetonemia secondary to another condition which reduces the cow's feed intake.
Wikipedia: Ketosis
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Ketosis
Classification and external resources

Ketone bodies
ICD-9 276.2
DiseasesDB 29485
MeSH D007662

In biology, ketosis (pronounced /kɪˈtəʊsɪs/) is a state of the organism characterised by elevated levels of ketone bodies in the blood, occurring when the liver converts fat into fatty acids and ketone bodies (which can be used for energy as an alternative to glucose).

Contents

Metabolic pathways

Ketone bodies, from the breakdown of fatty acids to acetyl groups, are also produced during this state, and are burned throughout the body. Excess ketone bodies will slowly decarboxylate into acetone. That molecule is excreted in the breath and urine. When glycogen stores are not available in the cells (glycogen is primarily created when carbohydrates such as starch and sugar are consumed in the diet), 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 where fatty acid chains are cleaved to form acetyl-CoA, which can then be fed into the Krebs Cycle. It is important to note that acetyl-CoA can only enter the Krebs Cycle bound to oxaloacetate. When carbohydrate supplies are inadequate, however, the liver naturally converts oxaloacetate to glucose via gluconeogenesis for use by the brain and other tissues. When acetyl CoA does not bind with oxaloacetate, the liver converts it to ketones (or ketone bodies), leading to a state of ketosis. During this process a high concentration of glucagon is present in the serum and this inactivates hexokinase and phosphofructokinase-1 (regulators of glycolysis) indirectly, causing most cells in the body to use fatty acids as their primary energy source. At the same time, glucose is synthesized in the liver from lactic acid, glucogenic amino acids, and glycerol, in a process called gluconeogenesis. This glucose is used exclusively[clarification needed] for energy by cells such as neurons and red blood cells.[citation needed]

Similar conditions

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 signals 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.

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.

Whether ketosis is taking place can be checked by using special urine test strips such as Ketostix.

Ketosis is deliberately induced in the ketogenic diet used to treat epilepsy. Other uses of low-carbohydrate diets remain controversial.[1] [2]

Controversy

Some medical resources regard ketosis as a physiological state associated with chronic starvation.[citation needed] 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[3][4][5]. It should be remembered from the above discussion that 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 denovo 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.[6][7][8] 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[9]. 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[9].

See also

External links

Diabetic Ketoacidosis
Alcoholic Ketoacidosis

References

  1. ^ G.D Foster et al., NEJM2003;348:2082-90[1]
  2. ^ Bravata et al., "Efficacy and safety of low-carbohydrate diets: a systematic review." Journal of the American Medical Association, Apr, 2003; 289(14):1837-50[2]
  3. ^ High-Protein Diets, American Heart Association, 14 March 2008
  4. ^ [http://www.cancer.org/docroot/SPC/content/SPC_1_A_Low_Carb_Diet_to_Prevent_Cancer.asp Weighing In on Low-Carb Diets], The American Cancer Society, retrieved 12 March 2008
  5. ^ Karra, Cindy: Shape Up America! Reveals The Truth About Dieters, Shape Up America! (by former U.S. Surgeon General C. Everett Koop), 29 December 2003
  6. ^ Eaton, S. Boyd; Melvin Konner (31 Jan 1985). "Paleolithic nutrition: a consideration of its nature and current implications". New England Journal of Medicine 312 (5): 283–89. PMID 2981409. http://content.nejm.org/cgi/content/citation/312/5/283. 
  7. ^ Eades, M. et al. Protein Power Lifeplan[3]
  8. ^ William S Yancy, Jr, Marjorie Foy, Allison M Chalecki, Mary C Vernon, and Eric C Westman (2005). "A low-carbohydrate, ketogenic diet to treat type 2 diabetes". Journal of Nutrition and Metabolism 2: 34. doi:10.1186/1743-7075-2-34. 
  9. ^ a b Diets, Ketogenic; Performance Jo, Physical; Nutrition, .; Metabolism Ur, .; .; . N.; Impaired Physical Performance Is A. Common But Not Obligate Result Of A. Low Carbohydrate Diet. Lessons From Traditional Inuit Culture Indicate That Time For Adaptation, Optimized Sodium; Nutriture, Potassium et al. (2004), "TY - JOUR AU - Phinney, Stephen PY -", SN - 1 (1): 1743–7075, doi:10.1186/1743-7075-1-2, http://www.nutritionandmetabolism.com/content/1/1/2, retrieved 2009-10-29 

 
 

 

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Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.  Read more
World of the Body. The Oxford Companion to the Body. Copyright © 2001, 2003 by Oxford University Press. All rights reserved.  Read more
Food and Nutrition. A Dictionary of Food and Nutrition. Copyright © 1995, 2003, 2005 by A. E. Bender and D. A. Bender. All rights reserved.  Read more
Sports Science and Medicine. The Oxford Dictionary of Sports Science & Medicine. Copyright © Michael Kent 1998, 2006, 2007. All rights reserved.  Read more
Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Ketosis" Read more