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Benefits of low carb diets with exercise
When to cut carbs, when to eat around exercise, spacing between meals, importance of carbs and protein for break feast

What Is Ketosis? What Causes Ketosis?

Ketosis is a condition in which levels of ketones (ketone bodies) in the blood are elevated. Ketones are formed when glycogen stores in the liver have run out.

The ketones – acetoacetate and β-hydroxybutyrate – are used for energy. Ketones are small carbon fragments that are the fuel created by the breakdown of fat stores. Ketosis is potentially a serious condition if keytone levels go too high.

However, when the body is in ketosis the individual tends to feel less hungry, and will probably eat less than he/she might otherwise do. The body switches from being a carbohydrate-burning organism into a fat-burning one. The fat stores become a primary energy source, and the person loses weight. That is why low-carb diets have become popular, and effective, especially among obese people.

The modern human body in most societies usually metabolizes glucose from carbohydrates for energy purposes, rather than energy from fat. If there is not enough glucose (from carbohydrates) in the bloodstream the body draws on fat stores for fuel, causing the appearance of ketones in the blood. Ketones are produced by the liver from fatty acids.

We need proteins and fats for building and repairing tissue and cells – proteins and fats can also be sources of energy. If necessary, the body can get all its energy from fats and proteins.

Our brain can use glucose or ketones for energy; it cannot generally burn fat for energy. A study carried out at the Psychology Department of Tufts University in Medford, Massachusetts found that women on low- or zero-carb diets performed worse in memory or thinking tests than women whose diets were not low in carbs.

When there are plenty of carbohydrates in the body, it breaks them down into glucose, which is then converted into energy and transported into the cells of our body.

If glucose cannot be broken down, as may be the case if the insulin levels are too low, or if there is a lack of glucose, then the body has to break down stored fat and convert it into energy. Metabolizing fat raises blood ketone levels, leading to ketosis. Ketosis can occur with Type 1 diabetes (not enough insulin), alcoholism, starvation, and with a low-carb, high fat/protein diet.

Ketones consist of acetone, acetoacetate or beta-hydroxybutyrate. Very high ketone levels can be toxic, making the blood more acid, and may damage such organs as the kidneys and liver.

The human body tries to lower acetone (a ketone) levels by breathing it out, causing a sweet and fruity breath. We also reduce keytone levels by expelling them through our urine.

The Process of Ketosis

Ketosis is a form of acidosis, a disruption in the pH balance of your body that results from the presence of excessive ketones in your blood. Ketones, or ketone bodies, are a byproduct of fat metabolism. They are released when fat is broken down for energy. Ketosis is a condition that is common during starvation and acute attacks of diabetes. The presence of large amounts of ketone bodies in your bloodstream may lead to a condition called ketoacidosis, which may result in adverse side effects. Ketogenic diets, when supervised by qualified medical professionals, can lead to significant amounts of weight loss in obese individuals, and they have proved promising in the treatment and management of epilepsy and certain forms of cancer.


Ketosis results from the buildup of ketone bodies, which are a byproduct of fat metabolism. When blood sugar is not available for your body to be used as energy, your body will begin breaking down fat instead. When fat is broken down into glucose to be used for energy, ketone bodies are produced as a result, and circulate throughout your bloodstream, causing a state of ketosis. The ketone bodies are produced in your liver, and can be re-used for other metabolic processes involved in energy production, or excreted from your body through your urine.


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.

  • Gluconeogenesis (abbreviated GNG) is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as pyruvate, lactate, glycerol, glucogenic amino acids, and odd-chain fatty acids.

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, or as the intentional result of a ketogenic diet, 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.  The ketone body acetoacetate will slowly decarboxylate into acetone, a volatile compound that is both metabolized as an energy source and lost in the breath and urine.