|Classification and external resources|
Ketosis (pron.: //) is a state of elevated levels of ketone bodies in the body. It is almost always generalized throughout the body, with hyperketonemia, that is, an elevated level of ketone bodies in the blood. Ketone bodies are formed by ketogenesis when liver glycogen stores are depleted. The ketone bodies acetoacetate and β-hydroxybutyrate are used for energy.
Metabolic pathways 
When glycogen stores are not available in the cells, fat (triacylglycerol) is cleaved to provide 3 fatty acid chains and 1 glycerol molecule in a process known as lipolysis. Most of the body is able to use fatty acids as an alternative source of energy in a process called beta-oxidation. One of the products of beta-oxidation is acetyl-CoA, which can be further used in the citric acid cycle. During prolonged fasting or starvation, acetyl-CoA in the liver is used to produce ketone bodies instead, leading to a state of ketosis.
During starvation or a long physical training session, the body starts using fatty acids instead of glucose. The brain cannot use long-chain fatty acids for energy because they are completely albumin-bound and cannot cross the blood–brain barrier. Not all medium-chain fatty acids are bound to albumin. The unbound medium-chain fatty acids are soluble in the blood and can cross the blood–brain barrier. The ketone bodies produced in the liver can also cross the blood–brain barrier. In the brain, these ketone bodies are then incorporated into acetyl-CoA and used in the citric acid cycle.
Ketone bodies are acidic, but acid-base homeostasis in the blood is normally maintained through bicarbonate buffering, respiratory compensation to vary the amount of CO2 in the bloodstream, hydrogen ion absorption by tissue proteins and bone, and renal compensation through increased excretion of dihydrogen phosphate and ammonium ions. Prolonged excess of ketone bodies can overwhelm normal compensatory mechanisms, leading to acidosis if blood pH falls below 7.35.
There are two major causes of ketoacidosis:
- Most commonly, ketoacidosis is diabetic ketoacidosis (DKA), resulting from increased fat metabolism due to a shortage of insulin. It is associated primarily with type I diabetes, and may result in a diabetic coma if left untreated.
- Alcoholic ketoacidosis (AKA) presents infrequently, but can occur with acute alcohol intoxication, most often following a binge in alcoholics with acute or chronic liver or pancreatic disorders. Alcoholic ketoacidosis occurs more frequently following methanol or ethylene glycol intoxication than following intoxication with uncontaminated ethanol.
If the diet is changed from one that is high in carbohydrates to one 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, blood glucose levels are maintained through gluconeogenesis, and the adult brain does not burn ketones. However, the brain makes immediate use of ketones for lipid synthesis in the brain. After about 48 hours of this process, the brain starts burning ketones in order to more directly use 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. The strips have a small pad on the end which is dipped in a fresh specimen of urine. Within a matter of seconds, the strip changes color indicating the level of ketone bodies detected, which reflects the degree of ketonuria, which, in turn, can be used to give a rough estimation of the level of hyperketonemia in the body (see table below). Alternatively, some products targeted to diabetics such as the Abbott Precision Xtra or the Nova Max can be used to take a blood sample and measure the ketone levels directly. Normal serum reference ranges for ketone bodies are 0.5–3.0 mg/dL, equivalent to 0.05–0.29 mmol/L.
Also, when the body is in ketosis, one's breath may smell of acetone. This is due to the break down of of acetoacetic acid into acetone and carbon dioxide which is exhaled through the lungs. Some find the smell offensive. Acetone is the same chemical responsible for the smell of nail polish remover and some paint thinners.
|Designation||Approximate serum concentration|
|0||Negative||Reference range: 0.5–3.0||0.05–0.29|
|1+||5 (interquartile range
|0.5 (IQR: 0.1–0.9)|
|2+||Ketonuria||7 (IQR: 2–19)||0.7 (IQR: 0.2–1.8)|
|3+||30 (IQR: 14–54)||3 (IQR: 1.4–5.2)|
Some clinicians regard restricting a diet from all carbohydrates as unhealthy and dangerous. However, it isn't necessary to completely eliminate all carbohydrates from the diet in order to achieve a state of ketosis. Other clinicians regard ketosis as a safe biochemical process that occurs during the fat-burning state. Ketogenesis can occur solely from the byproduct of fat degradation: acetyl-CoA. Ketosis, which is accompanied by gluconeogenesis (the creation of glucose de novo from pyruvate), is the specific state with which some clinicians are concerned. However, it is unlikely for a normal functioning person to reach life-threatening levels of ketosis, defined as serum beta-hydroxybutyrate (B-OHB) levels above 15 millimolar (mM) compared to ketogenic diets among non diabetics which "rarely run serum B-OHB levels above 3 mM." This is avoided with proper basal secretion of pancreatic insulin. People who are unable to secrete basal insulin, such as type I diabetics and long-term type II diabetics, are liable to enter an unsafe level of ketosis, causing an eventual comatose state that requires emergency medical treatment.
The anti-ketosis conclusions have been challenged by a number of doctors and advocates of low-carbohydrate diets, who dispute assertions that the body has a preference for glucose and that there are dangers associated with ketosis. Because of the experience of Arctic explorers like Vilhjalmur Stefansson who adopted native Inuit diets which derived as much as 90% of energy from fats and proteins, many have held up the Inuit people as an example of a culture that has lived for thousands of years on a ketogenic diet. Conversely, it is speculated by Nick Lane  that the Inuit may have a genetic predisposition allowing them to eat a ketogenic diet and remain healthy. According to this view, such an evolutionary adaptation would have been caused by environmental stresses. This speculation is unsupported, however, in light of the many arctic explorers, including John Rae, Fridtjof Nansen, and Frederick Schwatka, who adapted to native ketogenic diets with no adverse effects. Note especially Schwatka, who specifically commented that after a 2- to 3-week period of adaptation to the ketogenic diet of the native peoples he could manage "prolonged sledge journeys," including the longest sledge journey on record, relying solely on the Inuit diet without difficulty. Furthermore, in a comprehensive review of the anthropological and nutritional evidence collected on 229 hunter-gatherer societies it was found that, "Most (73%) of the worldwide hunter-gatherer societies derived >50% (≥56–65% of energy) of their subsistence from animal foods, whereas only 14% of these societies derived >50% (≥56–65% of energy) of their subsistence from gathered plant foods," suggesting that the ability to thrive on ketogenic diets is widespread and not limited to any particular genetic predisposition. While it is believed that carbohydrate intake after exercise is the most effective way of replacing depleted glycogen stores, studies have shown that, after a period of 2–4 weeks of adaptation, physical endurance (as opposed to physical intensity) is unaffected by ketosis, as long as the diet contains high amounts of fat. It seems appropriate that some clinicians refer to this period of keto-adaptation as the "Schwatka Imperative" after the explorer who first identified the transition period from glucose-adaptation to keto-adaptation.
Veterinary medicine 
In dairy cattle, ketosis is a common ailment that usually occurs during the first weeks after giving birth to a calf. Ketosis is in these cases sometimes referred to as acetonemia. A study from 2011 revealed that whether ketosis is developed or not depends on the lipids a cow uses to create butterfat. Animals prone to ketosis mobilize fatty acids from adipose tissue, while robust animals create fatty acids from blood phosphatidylcholine (lecithin). Healthy animals can be recognized by high levels of milk glycerophosphocholine and low levels of milk phosphocholine.
In sheep, ketosis, evidenced by hyperketonemia with beta-hydroxybutyrate in blood over 0.7 mmol/L, occurs in pregnancy toxemia. This may develop in late pregnancy in ewes bearing multiple fetuses, and is associated with the considerable glucose demands of the conceptuses. In ruminants, because most glucose in the digestive tract is metabolized by rumen organisms, glucose must be supplied by gluconeogenesis, for which propionate (produced by rumen bacteria and absorbed across the rumen wall) is normally the principal substrate in sheep, with other gluconeogenic substrates increasing in importance when glucose demand is high or propionate is limited. Pregnancy toxemia is most likely to occur in late pregnancy because most fetal growth (and hence most glucose demand) occurs in the final weeks of gestation; it may be triggered by insufficient feed energy intake (anorexia due to weather conditions, stress or other causes), necessitating reliance on hydrolysis of stored triglyceride, with the glycerol moiety being used in gluconeogenesis and the fatty acid moieties being subject to oxidation, producing ketone bodies. Among ewes with pregnancy toxemia, beta-hydroxybutyrate in blood tends to be higher in those that die than in survivors. Prompt recovery may occur with natural parturition, Caesarean section or induced abortion. Prevention (through appropriate feeding and other management) is more effective than treatment of advanced stages of ovine ketosis.
See also 
- Ketogenic diet
- Low-carbohydrate diet
- Spontaneous human combustion, for which acetone produced by ketosis has been suggested as a cause.
- Very-low-calorie diet
- thefreedictionary.com/ketosis citing:
- The American Heritage® Medical Dictionary Copyright © 2007
- Mosby's Medical Dictionary, 8th edition. © 2009
- Dorland's Medical Dictionary for Health Consumers. © 2007
- Harvey & Champe, biochemistry
- Robert C Johnson, Susan K Young, Richard Cotter, Lawrence Lin, and W Bruce Rowe (1990). "Medium-chain-triglyceride lipid emulsion: metabolism and tissue distribution". Am J Clin Nutr 52 (3): 502–8.
- Marshall, William J.; Bangert, Stephen K. (2008). Clinical biochemistry: metabolic and clinical aspects. Elsevier Health Sciences. pp. 67–80. ISBN 978-0-443-10186-1.
- Kitabchi AE, Umpierrez GE, Murphy MB, Kreisberg RA (December 2006). "Hyperglycemic crises in adult patients with diabetes: a consensus statement from the American Diabetes Association". Diabetes Care 29 (12): 2739–48. doi:10.2337/dc06-9916. PMID 17130218.
- Kraut JA, Kurtz I (January 2008). "Toxic alcohol ingestions: clinical features, diagnosis, and management". Clinical Journal of the American Society of Nephrology : CJASN 3 (1): 208–25. doi:10.2215/CJN.03220807. PMID 18045860.
- Hartman AL, Vining EP (January 2007). "Clinical aspects of the ketogenic diet". Epilepsia 48 (1): 31–42. doi:10.1111/j.1528-1167.2007.00914.x. PMID 17241206.
- Delbridge E, Proietto J (2006). "State of the science: VLED (Very Low Energy Diet) for obesity". Asia Pac J Clin Nutr 15: 49–54. PMID 16928661.
- Eades, M. R. (2007-05-22). "Metabolism and Ketosis".
- Foster GD, Wyatt HR, Hill JO et al. (May 2003). "A randomized trial of a low-carbohydrate diet for obesity". N. Engl. J. Med. 348 (21): 2082–90. doi:10.1056/NEJMoa022207. PMID 12761365.
- Bravata DM, Sanders L, Huang J et al. (April 2003). "Efficacy and safety of low-carbohydrate diets: a systematic review". JAMA 289 (14): 1837–50. doi:10.1001/jama.289.14.1837. PMID 12684364.
- PTS PANELS™ Ketone Test Strips Information paper PS-002588E Rev. 2 10/05 by Polymer Technology Systems
- Converted from molar values, using average of 10.3 g/mol as used in: PTS PANELS™ Ketone Test Strips Information paper PS-002588E Rev. 2 10/05 by Polymer Technology Systems, and subsequently rounded to same number of significant figures as molar value
- Taboulet, P; Deconinck, N; Thurel, A; Haas, L; Manamani, J; Porcher, R; Schmit, C; Fontaine, J et al. (2007). "Correlation between urine ketones (acetoacetate) and capillary blood ketones (3-beta-hydroxybutyrate) in hyperglycaemic patients". Diabetes & Metabolism 33 (2): 135–139. doi:10.1016/j.diabet.2006.11.006.
- Sekizawa, A; Sugito, Y; Iwasaki, M; Watanabe, A; Jimbo, M; Hoshi, S; Saito, H; Okai, T (2001). "Cell-free fetal DNA is increased in plasma of women with hyperemesis gravidarum". Clinical chemistry 47 (12): 2164–5. PMID 11719487. 
- Burbos, Nikolaos; Shiner, Alice M.; Morris, Edward (2008). "Severe metabolic acidosis as a consequence of acute starvation in pregnancy". Archives of Gynecology and Obstetrics 279 (3): 399–400. doi:10.1007/s00404-008-0715-3. PMID 18592261.
- 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
- Volek, Jeff S.; Stephen D. Phinney (2011). The Art and Science of Low Carbohydrate Living. Beyond Obesity. p. 302. ISBN 978-0-9834907-0-8.
- Volek and Phinney, p. 4
- Eaton, S. Boyd; Melvin Konner (31 January 1985). "Paleolithic nutrition: a consideration of its nature and current implications". N. Engl. J. Med. 312 (5): 283–89. doi:10.1056/NEJM198501313120505. PMID 2981409.
- Eades, M. et al. Protein Power Lifeplan
- 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. PMC 1325029. PMID 16318637.
- Lane, Nick (2005). Power Sex Suicide Mitochondria and the Meaning of Life. pp. 254–256. ISBN 0-19-280481-2.
- Phinney, Stephen D. (2004). "Ketogenic diets and physical performance". Nutrition & Metabolism 1 (1): 2. doi:10.1186/1743-7075-1-2. PMC 524027. PMID 15507148.
- "Vilhjalmur Stefansson – Low-carbohydrate diet of meat and fish". Wikipedia. Retrieved 2012-03-27.
- Schwatka, Frederick (1965). The Long Arctic Search. Ed. Edouard A. Stackpole. New Bedford, Mass.: Reynolds-DeWalt. p.115.
- Cordain, L., J. B. Miller, S. B. Eaton, N. Mann, S. H. Holt, and J.D. Speth (2000). "Plant-Animal Subsistence Ratios and Macronutrient Energy Estimations in Worldwide Hunter-Gatherer Diets.". American Journal of Clinical Nutrition 71 (3): 682–92.
- J. L., Ivy (Jun,19). "Glycogen Resynthesis After Exercise: Effect of Carbohydrate Intake". Int J Sports Med 19: S142–5. doi:10.1055/s-2007-971981. PMID 9694422.
- Burke, LM; Collier, GR; Hargreaves, M (August 1993). "Muscle glycogen storage after prolonged exercise: effect of the glycemic index of carbohydrate feedings". Journal of Applied Physiology. 2 75 (2): 1019–1023. PMID 8226443.
- Volek and Phinney, p. 237
- Klein MS, Buttchereit N, Miemczyk SP, et al. (February 2012). "NMR metabolomic analysis of dairy cows reveals milk glycerophosphocholine to phosphocholine ratio as prognostic biomarker for risk of ketosis". J. Proteome Res. 11 (2): 1373–81. doi:10.1021/pr201017n. PMID 22098372.
- Pugh, D. G. 2002. Sheep and goat medicine. Saunders, Philadelphia. 468 pp.
- Kimberling, C. V. 1988. Jensen and Swift's diseases of sheep. 3rd Ed. Lea & Febiger, Philadelphia. 394 pp.
- Marteniuk J. V., Herdt T. H. (1988). "Pregnancy toxemia and ketosis of ewes and does". Vet. Clin. North. Am. Food Anim. Pract 4: 307–315.
- Reid R. L. (1960). "Studies on the carbohydrate metabolism of sheep. IX. Metabolic effects of glucose and glycerol in undernourished pregnant ewes and in ewes with pregnancy toxaemia". Aust. J. Agr. Res. 11: 42–47.
- Van Soest, P. J. 1994. Nutritional ecology of the ruminant. 2nd Ed. Cornell Univ. Press. 476 pp.
- Overton T. R., Drackley J. K., Ottemann-Abbamonte C. J., Beaulieu A. D., Emmert L. S., Clark J. H. (1999). "Substrate utilization for hepatic gluconeogenesis is altered by increased glucose demand in ruminants. J. Anim". Sci 77: 1940–1951.
- Sasaki S., Ambo K., Muramatsu M., Tsuda T. (1975). "Gluconeogenesis in the kidney-cortex slices of normal fed and starved sheep". Tohoku J. Agr. Res. 26: 20–29.
- Henze P., Bickhardt K., Fuhrmann H., Sallmann H. P. (1998). "Spontaneous pregnancy toxaemia (ketosis) in sheep and the role of insulin". J. Vet. Med. Ser. A. 45: 255–266.
- Kahn, C. M. (ed.) 2005. Merck veterinary manual. 9th Ed. Merck & Co., Inc., Whitehouse Station.
- Diabetic Ketoacidosis at eMedicine
- NHS Direct: Ketosis
- Musa-Veloso K, Likhodii SS, Cunnane SC (July 2002). "Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals". Am. J. Clin. Nutr. 76 (1): 65–70. PMID 12081817.
- The Merck Manual —