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. It is seen in conditions in which the body produces excess ketones as an alternative source of energy.

It is seen during starvation or more commonly in type I diabetes mellitus. Production of ketone bodies is a normal response to a shortage of glucose, meant to provide an alternate source of fuel from fatty acids. For instance, after 24 hours of fasting the blood will have increased levels of ketone bodies (called ketonemia or ketosis), but all of it will be used by the muscles and very little will remain to be excreted in urine. PathophysiologyKetones are metabolic end-products of fatty acid metabolism. In healthy individuals, ketones are formed in the liver and are completely metabolized so that only negligible amounts appear in the urine. However, when carbohydrates are unavailable or unable to be used as an energy source, fat becomes the predominant body fuel instead of carbohydrates and excessive amounts of ketones are formed as a metabolic byproduct. Higher levels of ketones in the urine indicate that the body is using fat as the major source of energy.Ketone bodies that commonly appear in the urine when fats are burned for energy are acetoacetate and beta-hydroxybutyric acid.

The gas acetone is also produced, but is exhaled. Normally, the urine should not contain a noticeable concentration of ketones to give a positive reading. As with tests for glucose, acetone can be tested by a dipstick or by a tablet. The results are reported as small, moderate, or large amounts of acetone. A small amount of acetone is a value under 20mg/dl; a moderate amount is a value of 30-40mg/dl, and a finding of 80mg/dl or greater is reported as a large amount. ScreeningScreening for ketonuria is done frequently for acutely ill patients, presurgical patients, and pregnant women. Any diabetic patient who has elevated levels of blood and urine glucose should be tested for urinary ketones. In addition, when diabetic treatment is being switched from insulin to oral hypoglycemic agents, the patient's urine should be monitored for ketonuria. The development of ketonuria within 24 hours after insulin withdrawal usually indicates a poor response to the oral hypoglycemic agents.

Diabetic patients who use oral hypoglycemic agents should have their urine tested regularly for glucose and ketones because oral hypoglycemic agents, unlike insulin, do not control diabetes when an acute infection or other illness develops.In conditions associated with acidosis, urinary ketones are tested to assess the severity of acidosis and to monitor treatment response. Urine ketones appear before there is any significant increase in blood ketones; therefore, urine ketone measurement is especially helpful in emergency situations. During pregnancy, early detection of ketonuria is essential because ketoacidosis is a factor associated with intrauterine death. Causes of ketosis and ketonuriaMetabolic abnormalities such as diabetes, renal glycosuria, or glycogen storage disease Dietary conditions such as starvation, fasting, high protein, or low.

Ketosis

Ketosis (pronounced /ki?'to?s?s/) is a state in metabolism occurring when the liver excessively converts fat into fatty acids and ketone bodies which can be used by the body for energy.Adipose tissue consists of highly specialized cells which store energy in the form of a triglyceride and release it upon hydrolysis in a process known as lipolysis, yielding three fatty acids and one glycerol molecule. These ketone bodies are a by-product of the lipid metabolic pathway after the fat is converted to energy. Ketoacidosis, by contrast, is the accumulation of excessive keto acids in the blood stream (specifically acetoacetate and beta-hydroxy butyrate). Metabolic pathwaysMost medical resources regard ketosis as a physiological state associated with chronic starvation.citation needed Glucose is regarded as the preferred energy source for all cells in the body with ketosis being regarded as a crisis reaction of the body to a lack of carbohydrates in the diet.

In recent years this viewpoint, both the body's preference for glucose and the dangers associated with ketosis, has been challenged by some doctors.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. 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 for energy by cells such as neurons and red blood cells.citation needed Similar conditionsKetosis 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.

DietIf the diet is changed from a highly glycemic diet to a diet that does not substantially contribute to blood glucose, the body goes through a set of stages to enter ketosis.