In each phase of our life we have specific dietary needs. Prof. Peter J. Aggett of the Lancashire Postgraduate School of Medicine and Health, University of Central Lancashire, UK, looks at an important moment in our life: when we start to eat our first solid foods.

The World Health Organisation (WHO) advises that after exclusive breast feeding for the first 4-6 months of life, the evolving nutritional requirements of infants should be met by nutritionally adequate and safe complementary feeds while breast feeding continues for up to two years of age or beyond.

This diversification of a baby's diet is a topic of debate centring on the best time to introduce complementary feeds, as well as on what these foods should be. Most, but not all, guidelines reflect those of the WHO, with a "mixed diet" being offered by 6 months of age. However, in some environments, where hygienic conditions are not good, in developed and developing countries alike, giving babies fluids or solids can increase their risk of infection. Consequently, some authorities argue that solids should not be introduced until "about 6 months".

This like many other issues concerning weaning practices is difficult to resolve because the practices are governed by tradition rather than by science. For example, many mothers, including those in populations which achieve the ideal of breast feeding in to the second year of life, give their infants solids as early as 2 months of age.

Studies in other mammals suggest that the introduction of foods as well as maternal milk occurs at a particular milestone in neurophysiological and metabolic development. These changes have not been well characterised in humans, but by 4 months of age infants have sufficient neuro-muscular coordination to swallow pureed foods as well as being able to discriminate between some tastes and textures. The infant's metabolic and immunological maturity is less clear.

Most authorities recommend that types of foods introduced initially should be gluten free cereals (rice is often used), vegetables, fruits and meat.

The best ways to deliver these foods is by spoon, and there is no benefit in mixing them with liquid feeds. Indeed, this practice might impair the acquisition of an infant's ability to cope with textured foods.

The pureed products can quite conveniently be prepared at home. One potential advantage of using commercially-prepared products is that they are often iron supplemented, but the efficiency with which this iron is absorbed by the infant varies according to the nature of the product, and of course, the infant's need for extra iron.

The later transition to less finely pureed solids occurs in the latter half of infancy (i.e. 6 to 12 months) when infants are learning to chew, and manage the more granular texture of mince etc., and to finger feed. Recommended finger foods include crusts, toast fingers, pieces of fruit, cooked vegetables and cooked meat.

The problems associated with introducing complementary foods too early include satiation of the infant's appetite leading to a reduced intake of breast milk, iron deficiency anaemia because solids reduce the absorption of iron from breast milk and increased risk of infections. There are risks of delayed weaning also. These include slower growth, and nutrient deficiencies particularly of iron, zinc, fat-soluble vitamins, and essential fatty acids.

It is not known how infants become immunologically tolerant of proteins in food. The development by babies of allergies, and immunological reactions in the intestine are related to the early introduction of complementary foods. It is not clear how breast feeding affects this risk. Some foods are more likely to cause reactions than others are.

Thus the avoidance of gluten at this stage is based on the association of the intestinal malabsorption syndrome, coeliac disease, with the early introduction of wheat. For this reason barley and oat cereals are usually offered before wheat and mixed cereals. When there is a family history of allergies, the cautious advice is to delay the introduction of foods such as cow milk, peanuts, soya, egg, fish and chicken, which have a known allergenicity, until at least after six and up to twelve months of age.

Early immunological adverse reactions vary according to local complementary foods; for example, compared with Europe, reactions to rice are common in Japan, as, were reactions to peanuts in the USA until the recent increase of these reactions in Europe. Reactions to peanuts and eggs may persist to adulthood, others, such as those to cow milk, might not. Unfortunately, there is no way to predict reliably the progress of individual children and their susceptibility to allergies and intolerances.

The influence of the early diet on later health may extend also to the metabolism of nutrients and the subsequent risk of conditions such as cardiovascular disease, late onset diabetes and high blood pressure. These and related possibilities show how crucial it is to optimise the introduction of complementary feeding not just with short term goals in mind but also with a view to later health.

FOOD TODAY 11/2000