Recommended Intakes of Protein for Growth

R. Passmore

The scientific approach to defining protein requirements for growth is measurements of nitrogen balances and changes in body composition of experimental animals and children, fed diets containing varying quantities of protein and amino acids. This approach was adopted in the 1965 FAO/WHO report.

An alternative approach, now being explored, is based on studies of protein turnover in individual tissue and the whole body, together with estimates of the efficiency of protein synthesis in tissues.

Both these approaches are beset with difficulties, of which perhaps the most fundamental is the fact that even in a child who is growing rapidly the protein requirements for growth are only a small fraction of those needed for their maintenance; further the need of maintenance is related to the dietary energy intake.

The 1965 FAO/WHO report is difficult reading for experienced nutritionists and nearly impossible for others. Inconsistencies appear to arise when the statements of requirements are converted into practical recommendations. These defects arise from inherent difficulties in the experimental approach and in my opinion are unlikely to be resolved in the next few years. As a result there is now much confusion amongst persons responsible for food planning both at national and international levels. An alternative approach is set out here which is simpler, but based on ad hoc experience rather than experimental findings.

A child seldom fails to thrive solely because his diet is inadequate in protein; the diet is usually also inadequate in energy and often in some of the essential minerals and vitamins. Further the requirements of proteins and of other nutrients are often raised by infection, trauma and perhaps other environmental stresses. Recommendations specifically related to protein are, it is suggested unrealistic.

The present recommended intakes for adults of proteins, vitamins and minerals have a liberal safety margin. If any community was provided with food sufficient to satisfy the appetite of all its members and with all the nutrients present in the proportions recommended for the reference man, the children in that community would almost certainly grow well. However foods are not evenly distributed amongst members of a family and in many communities foods of high quality are given preferentially to the adult males. Children have extra needs for these nutrients because of growth, the need here being generally small, and because of the greater incidence and severity of infections.

Insurance that an adult diet is satisfactory for children can be provided by recommending additional milk. This is of course no novel idea, but it can bear repetition. The infant is entirely dependent on milk for the first 3 months of life and for the remainder of the first year a milk or milk substitute should form a major part of the diet. In the next four years up to the fifth birthday, the child gradually comes to eat the normal food of the family, but milk should remain an important part of his diet during this period. After the age of five when the growth rate is slowed down, a child thrives on a normal adult diet, provided there is ample of it and the protein mixture is of good quality. However much experience shows that school milk is of great benefit to children from homes where the family diet is poor or only marginally adequate.

In planning the food supplies of a country or a community the protein requirements should be met if the food supply meets the energy requirements, of which 10 per cent comes from a protein mixture of good quality, and, in addition, milk or milk substitutes are provided for growing children and pregnant and lactating mothers. How much milk or milk substitute is needed?

Individual needs of course vary, but for planning purposes the following guide might be recommended:

If in any country the energy needs are met and milk or equivalent substitutes are available, distributed and utilized on the above scale, then it can be stated with confidence that the children will grow well and that protein-calorie malnutrition will be a rarity.

If the above recommendation is acceptable, then it is easy to calculate from demographic data the total annual milk requirement for children. An estimate of the production capacity of the dairy herds can then be made. Next, this figure is substracted from the milk requirement to give a figure for the requirement of a milk substitute. The latter figure provides a target for agriculturalists who have to provide the raw material for the milk substitute and for the industrialists who have to manufacture it. In countries where the milk supply is inadequate, it would be easy to set up the target, the nature of which is readily understandable and the idea behind it suitable for exposition by health educationalists (unlike the 1965 FAO/WHO Report on Proteins!).

There remains the difficult problem of naming and defining the milk substitutes. At least 20 accredited products have been prepared in various parts of the world each with a local or brand name. There is no reason why these names should not be used locally, but there is need for a generic term. Milk substitute is unsuitable because in English a substitute is inferior and the evidence is that these new products are nutritionally as good as milk. Various other terms are used, e.g. "fully formulated processed protein foods", which may be accurate, but hardly catches the imagination.

Electricians have preserved the names of Volt, Ampere, Ohm and Faraday in their everyday conversation. Similarly bacteriologists respect Pasteur, Bruce and Welch. The discovery of effective milk substitutes is perhaps the most important achievement of nutritionists and it is suggested that it would be proper to name them after a distinguished nutritionist. The names of the Frenchman, Boussingault, and the American, Mendel, two notable pioneers in the study of dietary proteins, have been suggested.

A Boussingault or fully formulated processed protein food would differ significantly in its composition in different parts of the world. To guide manufacturers and to protect the public, minimum standards would be necessary in terms of calorie, protein, vitamin and mineral content per unit of dry weight. Recommended amounts of Boussingaults for each age group would also be necessary.

This new approach to making recommendations for intakes of protein for growth is put forward for discussion. Critics may say that it is unscientific; and certainly it is based on empiricism and not scientific experimentation. It is claimed that it has two merits which outweigh this defect. The first is that it does not separate the need for protein from the needs for other nutrients. The second is that it is simple and can be explained in everyday speech either to a cabinet minister or to a poor mother.

Postscript - Should this empirical approach to recommended intakes be acceptable, the report should still contain a statement of the present scientific evidence on the precise requirements of protein for growth. Apart from its fundamental interest to nutritionists, such a statement would be of practical value to those responsible for the treatment in hospital and rehabilitation of children who have been severely malnourished.