KETOSIS – WHAT IS IT?*
Ketosis is a condition in which the levels of ketones, also called ketone bodies, in the blood are elevated.
Ketones or Ketone Bodies
The ketones, or ketone bodies – acetoacetic acid, beta-hydroxybutyric acid and acetone - are small carbon fragments that are the fuel created by the breakdown of fat stores. They are formed when liver and muscle glycogen stores are depleted. They are used for energy, especially in the brain.
Glucose is the fuel of the body. Excess glucose in the blood is removed from the blood under the influence of insulin and is stored as glycogen, mainly in the cells of the liver and muscles. Glycogen is a multi-branched polysaccharide of glucose. Muscle glycogen is converted to glucose by the muscle cells, to be used by the muscles, and liver glycogen converts to glucose for use throughout the body, including the central nervous system.
The citric acid cycle, known as the Krebs cycle or the tricarboxylic acid cycle, is one of the major metabolic pathways of cellular respiration and involves a cyclic series of enzymatic reactions (which take place in the mitochondria) by which pyruvate, converted into acetyl CoA, is completely oxidised to carbon dioxide and water to produce high-energy phosphate compounds, such as adenosine triphosphate (ATP), which are the source of cellular energy. Pyruvate is the end product of glycolysis, which is the metabolic pathway that converts glucose to pyruvate.
When glycogen stores are no longer available, fat (triacylglycerol) is split into fatty acids and glycerol in a process known as lipolysis. In the liver, the glycerol, via the process of glycolysis, is converted into pyruvate. Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substances such as pyruvate.
In other tissues, during high rates of fatty acid oxidation (beta-oxidation), large amounts of acetyl-Coenzyme A (CoA) are generated. These exceed the capacity of the citric acid cycle (tricarboxylic acid cycle) and result in the synthesis of the ketone bodies acetoacetic acid, beta-hydroxybutyric acid and acetone.
Although termed ketone ‘bodies’, they are molecules, not particles.
The ketone body acetoacetic acid will slowly decarboxylate into acetone, a volatile compound that is both metabolised as an energy source and excreted in the breath and urine, giving a characteristic "fruity" smell.
Ketosis or Ketoacidosis
Both acetoacetic acid and beta-hydroxybutyric acid are acidic, and if levels of these ketone bodies are too high, the pH of the blood drops, resulting in ketoacidosis (or just ‘acidosis’).
It is essential for health that the correct pH of the blood is maintained, a pH in the region of 7.4. The acid-base (acid/alkali) homeostasis in the blood is normally maintained through bicarbonate buffering, respiratory compensation to vary the amount of carbon dioxide in the blood stream, hydrogen ion absorption by tissue proteins and bone, and renal compensation through increased excretion of dihydrogen phosphate and ammonium ions. Minerals such as calcium (removed from bones) act as an immediate buffer until the above mechanisms restore homeostasis. Prolonged excess of ketones or ketone bodies can overwhelm the normal compensatory mechanisms, leading to ketoacidosis when the blood pH falls below 7.35.
Most commonly, ketoacidosis occurs in diabetes, resulting from increased fat metabolism due to a shortage of insulin. It is associated primarily with type 1 diabetes, but also in untreated type 2 diabetes, and may result in a diabetic coma if left untreated, a potentially life-threatening situation.
A mild ketoacidosis may occur in prolonged fasting or when following a ketogenic diet (high-fat, adequate protein but low-carbohydrate) or a very low calorie diet.
For a detailed discussion of the acid/alkaline balance in the body and the role of food in this, refer to my September 2005 newsletter Acid / Alkaline Balance - The Ideal Diet.
Diagnosis of Ketosis
Whether ketosis is present can be checked by using special urine test strips such as Ketostix. The strips have a small pad on the end which is dipped into a fresh specimen of urine. Within a matter of seconds, the strip changes colour indicating the level of ketone bodies detected, which reflects the level of hyper-ketonaemia in the body.
Blood levels of ketones can be measured directly.
When ketosis is present, there is the characteristic smell of acetone on the breath.
Is Ketosis Dangerous?
The National Health Service (NHS) UK describes ketosis as a potentially serious condition, whereas a number of popular diets (eg Atkins) cite ketosis as being as essential part of weight loss.
The NHS describes ketosis as being potentially dangerous as very high levels of ketosis, with resulting ketoacidosis, may lead to serious illness in a relatively short space of time.
*Copyright 2014: The Huntly Centre.
Disclaimer: All material in the huntlycentre.com.au website is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.
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