HM’s Food & Wine Magazine

Metabolism is the sum total of all the chemical changes that nutrients undergo from the time they are absorbed until they become part of the body or are excreted from the body. The first phase of metabolism is Anabolism which involves the chemical reaction that nutrients undergo for the construction or building up of materials, such as muscle, tissues, enzymes, hormones, blood or glycogens. The other phase is catabolism which involves all the practices in which various compounds of the tissues are broken down. Energy metabolism is the term generally used to describe all the chemical and physical changes that the energy nutrients undergo in the process of releasing energy for the body’s use.

During the digestive processes, the carbohydrates of foods are converted into the simple sugars, glucose, fructose, and lactose. The portal vein carries them from the intestinal tract to the liver. The liver releases into the blood as much of glucose as in normally needed for the body’s immediate use and stores the rest by converting it into glycogen or “animal starch.” The process by which glucose is converted into glycogen is called glycogenesis. Some glycogens are also stored in the muscles. The liver can store up to about 100 gms or 10 percent of its weight in glycogens whereas the storage capacity of the muscles is only about 2 percent of its weight.

Insulin is a hormone selected by the pancreas in carbohydrate metabolism. It facilitates the oxidation of glucose as well as the formation of glycogen. In diabetes mellitus, a metabolic disease, there is a decrease in the productions of insulin and the liver is not able to store the excess of glucose. Therefore, the glucose level in the blood reserves and the body is not able to utilize the carbohydrates and glucose is secreted in the urine.

Adrenalin is a hormone and act in a manner exactly opposite to that of insulin. It stimulates the breakdown of liver glycogen and causes the withdrawal of glucose from the liver leading to consequent rise of glucose in the blood. That is why; there is an outburst, such as anger, shock or fear. Thus supply feed for some immediate physical action like fighting or running when extra energy is required by the body or when it does not get sufficient food as during starvation, under nutrition and certain diseases, at that time glycogen which is stored in the liver is converted into glucose.

Most of glucose in the body is derived from the dietary carbohydrates, a small quantity of glucose may be formed in the liver from non- carbohydrate sources, for an example lactic acid which is formed by the breakdown of muscle glycogen. The glycerol part of fats and the deaminized portions of amino acids. The oxidation of glucose or glycogen for
release of energy is complex and involves many stages, in which several complex enzymes take part. Glucose or glycogen is first broken down to pyruvic and lactic acids and later on oxidized to release energy, forming carbon dioxide and water. At this stage the deaminized amino acids and the fatty acid parts of fats enter the metabolism cycle. When the carbohydrates are consumed in greater quantities than the energy requirement of the body, the excess is converted into fat and either stored in the tissues or used in the form of amino acids.

In metabolism of fats, the end-products of the digestion of fats are fatty acids and glycerol. They are absorbed from the intestinal tract and passed into the lymph vessels on their way to the cells and tissues of the body.  They are recombined to form fat molecules which unite milk phosphoric acid to form phospholipids, which aid in the transport of fatty acids in the body. The blood carries the fat, phospholipids, glycerol and fatty acids and distributes them to all parts of the body where they either oxidized for energy or stored as fatty tissues means get fatty body.

After metabolism of protein, amino acids are end-products which are absorbed into the blood stream immediately and passed into the liver from where they are distributed to the various cells of the body. The body uses the amino acids in three ways:

1.    Some amino acids are synthesized into protein to build new cells to replace worn-out cells and to form body  regulators such as hormones, enzymes , antibodies and  vitamins. Therefore the amino acids are used as “building blocks”.
2.    Some amino acids exchange their amino groups with other amino acids to form new amino acids peculiar to the species.
3.    The remaining amino acids are either converted into fats and carbohydrates or broken down to be used as fuel after oxidation.

Before oxidizing amino acids, their amino groups must be removed. This involves several steps and takes place in many of the tissues of the body, mainly in the liver and kidney. The amino group which is removed forms ammonia which is converted into urea and eliminated through urine.

All the three food factors, carbohydrates, fats and proteins are burnt in the body to yield energy for external muscular work and internal activity, the products of this burning are carbon dioxide, water, urea, and other nitrogenous constituents.  These are excreted through the lungs, skin and kidneys.  The excess of them is stored as fat.

Digestion and metabolism help toward the maintenance of the dynamic state of the “internal environment” of the body. The “internal environment” directly controls all life processes.