Ketosis
From Wikipedia, the free encyclopedia
| Ketosis Classification and external resources |
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|---|---|
| Ketone bodies | |
| ICD-9 | 276.2 |
| DiseasesDB | 29485 |
| MeSH | D007662 |
Ketosis (pronounced /kiːˈtoʊsɪs/) is a state 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 by all of the body for energy as an alternative to glucose). These ketone bodies are a by-product of the lipid metabolic pathway after the fat is converted to energy.[1][2][3][4][5] Ketoacidosis, by contrast, is the accumulation of excessive keto acids in the blood stream (specifically acetoacetate and beta-hydroxy butyrate). Whereas most consider ketoacidosis to be a medical condition, a minority of specialists believe that ketosis is not.
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[edit] Metabolic pathways
Most medical resources regard ketosis as a physiological state associated with chronic starvation.[citation needed] Glucose is the energy source used initially by cells in the body due to its availability within the cell; ketosis is regarded as a crisis reaction of the body due to a lack of carbohydrates in the diet. Ketosis would thus be a dangerous (potentially life-threatening) state which unnecessarily stresses the liver and causes destruction of muscle tissues. This is still the view of the majority in the medical and nutritional science communities[6][7][8], but in recent years it has been challenged by a number of doctors and adherents of low-carbohydrate diets, who dispute both the body's preference for glucose and the dangers associated with ketosis.[9][10][11]
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]
[edit] 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.
[edit] 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 takes place can be checked by using special urine test strips such as Ketostix.
Deliberately induced ketosis through a low-carbohydrate diet has been used to treat medical conditions although most such treatments remain controversial.[12] [13]
[edit] See also
[edit] External links
- Diabetic Ketoacidosis
- NHS Direct: Ketosis
- Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals, American Journal of Clinical Nutrition.
- The Merck Manual -
[edit] References
- ^ "http://www.jhu.edu/~jhumag/495web/fat.html", Johns Hopkins University, http://www.jhu.edu/~jhumag/495web/fat.html
- ^ "http://www.med.upenn.edu/nutrimed/MedNutandDisSampleCase.shtml", University of Pennsylvania School of Medicine, http://www.med.upenn.edu/nutrimed/MedNutandDisSampleCase.shtml
- ^ "http://www.med.umich.edu/diabetes/patients/dictionary.htm", University of Michigan Medical School, http://www.med.umich.edu/diabetes/patients/dictionary.htm
- ^ "http://www.orcbs.msu.edu/occupational/programs_guidelines/right_to_know/gloss/ketosis.htm", Michigan State University, http://www.orcbs.msu.edu/occupational/programs_guidelines/right_to_know/gloss/ketosis.htm
- ^ "http://depts.washington.edu/chdd/outlook/outlook00_13.1.pdf" (PDF), University of Washington School of Medicine, http://depts.washington.edu/chdd/outlook/outlook00_13.1.pdf
- ^ High-Protein Diets, American Heart Association, 14 March 2008
- ^ [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
- ^ 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
- ^ Eaton, S. Boyd; Melvin Konner (1985). "Paleolithic nutrition: a consideration of its nature and current implications". New England Journal of Medicine 312: 283–89. PMID 2981409. http://content.nejm.org/cgi/content/citation/312/5/283.
- ^ Eades, M. et al. Protein Power Lifeplan[1]
- ^ 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:.
- ^ G.D Foster et al, NEJM2003;348:2082-90[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[3]
