“I answer 20,000 letters a year and a lot of couples have problems because they don’t get adequate protein and vitamins.”

Barbara Cartland, English novelist.

The Observer (London) “Sayings of the Week” (31 August 1986).

There are three nutrients that produce energy: carbohydrates, proteins and fats. These nutrients are written on the following lines.

1. Carbohydrates. Carbohydrates generally provide most of the energy in a normal diet, but no single carbohydrate is an essential nutrient in the sense that the body needs it but cannot make it on its own from other nutrients. If carbohydrate intake is less than 100g per day, ketosis is likely to occur.

2. Fats. Due to their high caloric value, fats are useful for people with a high energy expenditure; In addition, they are useful for cooking and making food appetizing. Although rats require linoleic or arachidonic acids in their diet, deficiency of essential fatty acids is rare in man. It has been shown in patients who have been fed intravenously for long periods without fat emulsions. They develop a desquamative dermatitis and eicosatrienoic acid accumulates in plasma lipids. Essential fatty acids are precursors for prostaglandin synthesis.

3. Protein. Proteins provide about 20 amino acids, eight of which are essential for normal protein synthesis and for maintaining nitrogen balance in adults. These essential amino acids are methionine, lysine, tryptophan, phenylalanine, leucine, isoleucine, threonine, and valine. Histidine and perhaps arginine are also necessary for the growth of babies.

The ‘biological value’ of different proteins depends on the relative proportions of essential amino acids they contain. Animal-based proteins, particularly from eggs, milk, and meat, are generally of higher biological value than plant-based proteins that are deficient in one or more of the essential amino acids. However, it is possible to have a diet of mixed vegetable proteins with a high biological value if the principle of supplementation is used. For example, grains such as wheat contain about 10% protein and are relatively deficient in lysine. Vegetables contain about 20% protein that is relatively deficient in methionine. If two parts of wheat are mixed (or eaten) with one part of vegetables, a food containing 13% of a protein of high biological value is obtained. This happens because grains contain enough methionine and vegetables enough lysine to complement the other component of the mix.

The usual amount recommended for adequate protein intake is 10% of total calories, or about 65g for an average adult. The minimum requirement is less than 40 g per day of protein of good biological value for an adult.