单项选择题

Increasingly, over the past ten years, people—especially young people—have become aware of the need to change their eating habits, because much of the food they eat, particularly processed foods, is not good for the health.
Consequently, there has been a growing interest in natural foods, foods which do not contain chemical additives and which have not been affected by chemical fertilizers, widely used in farming today.
Natural foods, for example, are vegetables, fruits and grains which have been grown in soil that is rich in organic matter. In simple terms, this means that the soil has been nourished by unused vegetable matter, which provides it with essential vitamins and minerals. This in itself is a natural process compared with the use of chemicals and fertilizers, the main purpose of which is to increase the amount—but not the quality-of foods grown in commercial farming areas.
Natural foods also include animals which have been allowed to feed and move freely in healthy pastures. Compare this with what happens in the mass production of poultry: there are battery farms, for example, where thousands of chickens live crowded together in one building and are fed on food which is little better than rubbish. Chickens kept in this way are not only tasteless as food; they also produce eggs which lack important vitamins.
There are other aspects of healthy eating which are now receiving increasing attention from experts on diet.
It is significant that nowadays fibre is considered to be an important part of a healthy diet. In white bread, for example, the fibre has been removed. But it is present in unrefined flour and of course in vegetables. It is interesting to note that in countries where the national diet contains large quantities of unrefined flour and vegetables, certain diseases are comparatively rare. Hence the emphasis is placed on the eating of wholemeal bread and more vegetables by modern experts on "healthy eating". In the last paragraph, people are recommended to have ______.