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How fat is used as energy PDF Print E-mail


Unsaturated fats are typically called oils but the term oil can be confusing, because it is also used for substances having no relation to lipids or dietary fats, such as mineral oil or lubricating oil. To keep this clear in your mind, remember that the word oil indicates the physical state of a substance, not its chemical nature.

Adding to the potential confusion is the fact that the hardness or consistency of a fat, which is related to its melting point, can’t be fixed too precisely because fats are generally mixtures rather than pure substances. Dietary fats often contain some of both saturated and unsaturated fatty acids.

Also, the colour of a fat has nothing to do with the issue. Animal fats, for example, derive their color from the pigments present in the diet of the animal.

The Difference Between Adipose Tissue And Structural Fat

When we talk about body fat, we differentiate between adipose tissue and structural fat.

  • Structural fat is the body fat that is essential for the protection of the internal organs, for building parts of the brain, and for the development and maintenance of body cells, nerves and hormones. These are present as more complex lipids, such as phospholipids and cholesterol.
  • Adipose tissue (the spare tyre around our bellies) is made up mostly of simple fats.


Ketone Production

When fats are absorbed through the walls of the small intestines, the glycerol is separated from the fatty acids, and the fatty acids are broken into pieces in the liver. The pieces are known as ketone bodies.

Ketone bodies are used as a source of energy, and like glucose, ketone bodies eventually become carbon dioxide and water. The production of ketone bodies is a part of normal fat metabolism, and it is the way that fat is used.

The amount of ketones formed in the liver depends on the amount of glucose or glycogen (stored glucose) available for use as energy. This reverse ratio means that fewer ketones will be produced in the presence of a lot of glucose. The reason for this is that insulin depresses the formation of ketone bodies. When glucose is being used for energy, ketones are not needed in large amounts. On the other hand, in the absence of adequate insulin, the body metabolizes stored fats to produce the energy that the body’s tissues require.

The action of the pituitary gland on the formation of ketones is just the opposite. Pituitary hormones mobilize fat, and favour the formation of ketones in the liver, thereby decreasing the power of tissues to consume glucose.

What Is Ketosis?

When the glucose available for energy use exceeds the tissues’ needs, the glucose, under the influence of insulin, is converted to glycogen and to body fat. But when there are more ketone bodies available for energy use than are needed by the tissues, they cannot be converted into fat storage. They accumulate in the blood, and are excreted in the urine. This is called ketosis.

One of the ketone bodies is called acetone, and it is the chemical that is detected on urine ketone dip sticks.

Ketone production results from the breakdown of body fats. The excretion of the excess ketones in the urine is important because the presence of large amounts of ketone bodies in the blood threatens to upset the acid-alkaline balance of the blood, and thereby, the balance in the tissues.

If you follow a very low carbohydrate diet, and thereby reduce the amount of glucose and insulin circulating in your blood, your body will manufacture increased amounts of ketones, as it uses your stored body fat for its energy needs. In this case, we generally consider the ketosis to be a good thing because excess adipose body fat is being used and discarded.

Some authorities have referred to this kind of ketosis as benign dietary ketosis, or lipolysis ketosis. Lipolysis means fat destruction.

The Controversy

The ketosis controversy stems from the fact that there is another kind of ketosis, more properly called ketoacidosis (keto-ACID-dough-sis). This type of ketosis occurs in serious diabetes, in the total or almost total absence of insulin. It is quite dangerous, and is associated with kidney disease and with certain blood and brain dysfunctions.

Confusion between these two types of ketosis leads some scientists and some doctors to consider all ketosis to be inadvisable. Since the production of ketones can be prevented by the presence of carbohydrates, some consider the low carbohydrate diet to be dangerous as well.

In this regard, a very famous phrase was repeated for decades, and is still repeated among those who advocate a high carbohydrate, low fat diet. The phrase is “Fat burns in the fire of carbohydrates.” This means that fat is utilized when carbohydrate is metabolized. But one of the major problems with this viewpoint is the well-known fact that fats are always used by the cells, no matter how abundant – or how meager – the supply of carbohydrates may be.

The bottom line is that unless there is complete or nearly complete absence of insulin, there will be no ketoacidosis problem arising from the formation of ketones, thus ketoacidosis is unlikely to occur in healthy individuals whereas ketosis (which is safer) will. However, if you are embarking on a radical new dietary change, it is always advisable to consult your healthcare provider in order to discuss the possible dangers that may be associated with drastic changes especailly if you are already being treated for various health issues the likes of diabetes or cardiovascular disease.