What are enzymes?

Like any other machine, the body also needs energy to work. This energy is obtained from the food materials through metabolism. Some activating agents or catalysts called enzymes carry on the metabolic processes efficiently. Do you know what these enzymes are and what they do in our body?

 An enzyme is an organic catalyst produced by a living cell. The human body literally contains hundreds of different enzymes. Many are contained within the cells, but some others, such as those used for digestive purposes, act outside cells in the gut itself. Enzymes are involved in almost every chemical reaction-taking place in the body.

Many physiological activities such as digestion, building up and breakdown of tissues, cellular respiration and muscle contraction depend on their action. The activity of an enzyme, depends on the temperature, the degree of acidity or alkalinity (pH) and the substance upon which the enzyme acts. A single enzyme molecule is capable of bringing about the required changes on hundreds of molecules of the substrate in a few seconds. All the enzymes are themselves proteins and made up on long chains of amino acids. They combine with the substrate to form an intermediate compound. This intermediate compound is an unstable complex and breaks down to yield the reaction product plus the original enzyme.

Some poisonous substances such as mercury, lead or arsenic can block enzyme action. The presence of such substances hinders the enzymes from forming intermediate complex with the substrate. Normal metabolism is thus prevented. Enzymes are not only important for our body but are also very useful in industry, medicine and analytical chemistry. They are used to convert starch into glucose and glucose into fructose. They are also used in cheese-making industry and for the production of semi synthetic penicillins. Artificial sweeteners are also produced with their help.

Enzymes are classified into six major groups: Oxidases, which bring about oxidation, transferases, which bring about group transfer; hydrolases, which speed up the process of hydrolysis; lyases that bring about group removal. Isomerases enzymes are responsible for isomerization and ligases for joining of molecules.

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SO WHERE DO THOSE EXTRAS POUNDS COME FROM?

As we saw in Chapter I, an excess of "Calories taken in" over "calories burned up" does not in itself explain why we put on weight. In other words, it does not account for how the body comes to store fat. There has to be some other explanation, and that is what we shall look at in this chapter.

INSULIN

Whether or not we accumulate body fat is directly linked to the secretion of insulin, so we will first take a brief look at this. Insulin is a hormone secreted by the pancreas and it plays a vital role in human metabolism. Its function is to act on the glucose (i.e. the sugar) in the bloodstream in such a way that the glucose is absorbed into the body's tissues. The glucose can then either be used to satisfy the body's immediate energy needs or, if there is a surplus, it can be stored as body fat.

So let us look at a few hypothetical examples to see under what conditions and with what types of food body fat is likely to be produced, and to what extent.

INGESTING A CARBOHYDRATE

Let us take the example of a piece of bread, eaten on its own.

Bread is a carbohydrate, whose starch is broken down into glucose, which in turn passes directly into the bloodstream. The body is suddenly in a state of hyperglycaemia (that is, the level of glucose in the blood is raised). The pancreas thereupon secretes insulin in order to:

1. release the glucose into the body tissues, either to be stored short-term as glycogen which will

be used for the body's immediate needs, or to be stored for the longer term in the form of body fat.

2. lower the blood glucose level (see chapter on hypoglycaemia).

INGESTING A CARBOHYDRATE WITH A LIPID

When, for example, you eat a piece of bread with butter, the metabolic process is similar to the one described in the previous paragraph. The carbohydrate is broken down into glucose; the blood glucose level rises; the pancreas secretes insulin. However, there is a fundamental difference. In this example the lipid is converted into a fatty acid in the blood.

If the pancreas is in perfect condition, the quantity of insulin secreted will be exactly right for the amount of glucose to be dealt with. If, on the other hand, the pancreas is defective, the amount of insulin released may be greater than is needed to deal with the glucose. The result is that a part of the lipid's energy, which would normally simply be eliminated, will in this instance be stored as body fat. So you can now see that it is the condition of the pancreas that determines whether an individual will tend toward plumpness or will be able to eat absolutely anything without putting on an ounce: the person who puts on weight easily has a tendency to hyperinsulinism.

INGESTING A LIPID ON ITS OWN

Let us take as our example a piece of cheese, eaten on its own. The metabolism of a lipid on its own involves no release of glucose into the bloodstream. Consequently, the pancreas secretes virtually no insulin. In the absence of insulin, the energy cannot be stored away as fat. That does not mean that ingesting the lipid has served no purpose. During the process of digestion the body extracts from it all the substances essential to its metabolism, particularly vitamins, essential fatty acids and minerals (such as calcium from milk).

This example has been deliberately simplified. Even though it is based on sound scientific principles, you may be inclined to smile at its apparent simplicity. For, as you will have guessed, the reality is somewhat more complicated.

The example does illustrate, though, the essence of the process we are looking at, and the essence of what we need to know in order to understand the basic rules we are going to take as our guide.

But although this chapter seems to me the most important in the book, in that it shows how body fat is created, it will not yet have explained to you how, by continuing to eat perfectly normally, but " differently", you can shed all those unwanted pounds and then maintain your ideal weight.

Note : The pancreas is, in a sense, the conductor of the metabolic orchestra. If it is in good condition it will fulfil its role in bringing down the blood glucose level by secreting the appropriate amount of insulin. If it is not functioning well, if there is hyperinsulinism, it will tend to trigger the mechanisms which lay down fatty acids abnormally as body fat. So it is the pancreas, with its insulin-producing function, which turns out to be responsible for those extra pounds. However, we shall see later on that a diet with too much carbohydrate leads in the long term to pancreatic dysfunction .