"Food Today" No. 1 defined nutrition as the science of food in relation to health and also introduced a framework for studying nutrition's effects on the human body. The article in this issue reviews the role of the two key nutrient groups: macronutrients and micronutrients.

The word 'nutrient' is a broad term to describe all dietary substances used by the body to ensure normal development and maintain good health. The term, however, can be divided into two distinct groups of dietary components:

• macronutrients and
• micronutrients

Macronutrients are proteins, lipids (fats), and carbohydrates. They are the principal ingredients of the diet and are either the basic material from which the body is built (proteins and fats normally constitute 44% and 36% of the dry weight of the body, respectively), or the fuel required to run it (carbohydrates and fats ideally supply about 55% and 30% of our energy).

Water is also a macronutrient, but because we do not obtain any 'nourishment' from it (neither energy nor other essential components), it is often not considered as one. It is, however, the most important constituent of our body, quantitatively and qualitatively. Not only does water account for around 60% of our total body weight, it is also the component that we can afford to lose the least of. Generally, a loss of only 8% of our body water (about four litres) is sufficient to cause serious illness. This compares with about 15% for protein, the next most important, and up to 90% of fat, the least important.

Micronutrients, in contrast, provide virtually no energy but are the essential cofactors for metabolism to function. Micronutrients are primarily vitamins (e.g., vitamins A, B, C, D, E, and K), minerals (such as calcium and phosphorous), and trace elements (such as iron, zinc, selenium, and manganese).

Although these are required in very small amounts in the diet, they are nevertheless key dietary components. The processes of growth, energy production, and many other normal functions would not occur without them.

Health, consequently, is related to an optimum supply of both macronutrients and micronutrients. Insufficient or excess intake of either can lead to problems. In the world today, the main nutritional issues are primarily related to excess intake of macronutrients or insufficient intake of micronutrients. The next article in the series will look at an example of each.

FOOD TODAY 01/1998