Protein and Energy Needs in the First two Years of Life

Infants on average double their birth weight (3.3 kg), by four months (6.6 kg) and treble it by one year (9.9 kg). Growth is slower in the second year of life, an average of 2 to 2.5 kg in weight. Thus, it is not surprising that energy and protein requirements expressed per kilogram bodyweight are highest in the young infant and decrease modestly in the second year of life.

Recently at the request of the United Nation’s Sub-Committee on Nutrition, an international dietary energy consultative group has been established. The task of the Consultative Group was to review the 1985 FAO/WHO Report on Energy and Protein Requirements ¹, in light of more recent data in the literature. This group held a workshop in November of 1994 which was published as a supplement to the European Journal of Clinical Nutrition ². The purpose of the present article is to summarize for the clinician (dietitian, doctor or nurse) the new thoughts on the energy and protein needs of infants in the first two years of life, arising from the Consultative Group.

Energy Requirements

Energy requirements are made up of several components including resting or basal metabolic rate, diet-induced thermogenesis, growth, and activity (exercise). Only in young infants, due to their rapid growth, is it possible to measure, on a daily basis, the growth component ³. The important new observations relating to energy requirements of infants, comes from measurements of total daily energy expenditure. These measurements have been made possible in the past five to ten years, due to the development of a new technique which is known as double labelled water studies ⁴. These studies consist of giving the subject water in which the hydrogen is labelled with ²H and which the oxygen is labelled with ¹⁸O. Both of these traces are stable isotopes. Their excretion is followed in urine over a period of seven to ten days. The concentration of the ¹⁸O in urine water falls more rapidly than the ²H. CO ²production can be calculated from this difference in isotope clearance. Knowledge of the protein, fat and carbohydrate composition of the diet allows calculation of a food quotient. The food quotient is the result of the complete oxidation of the food to carbon dioxide and how much oxygen is required to do that. It is analogous to a respiratory quotient. Normal values are in the range of 0.85. It is therefore possible to calculate oxygen consumption as well as the measured carbon dioxide consumption. From these values of oxygen consumption and carbon dioxide production, it is possible to calculate, quite reliably, total daily energy expenditure. Using this type of methodology, careful studies have been done in infants principally at the Children’s Nutrition Research Center in Houston. The result is a realization that the daily expenditure of infants, particularly those who are breast fed, is considerably lower than the present energy requirements for infants ³. These lower values are seen in the first two months of life, after which, there is little or no important difference ^3,5 (table 1).

Protein Requirements

There are two components of protein requirements, that for maintenance, and that for growth. On a unit weight basis, the amount for maintenance appears to be constant at 90 mg of nitrogen/ kg per day. This is equivalent to 0.56 g of protein/ kg per day. Conversely, the nitrogen increment for growth in the first month of life is 160 mg of nitrogen/ kg per day and falls in a curvilinear fashion to a value of 24 mg of nitrogen/ kg per day, by the end of the first year of life. Safe levels of protein intake, which are listed in the table 2, take into account the sum of maintenance plus the growth increment and in addition take into account issues of protein digestibility. The values in table 2 relate to high quality protein coming from milk or egg. If the diet were completely vegetarian, then there would be a need to consider the amino acid balance of the diet. If the amino acid balance was not ideal, there might well be a need for higher protein intake. However, in practical terms, infants usually eat a mixed diet in which vegetable protein (e.g. cereal) is taken with animal protein (e.g. milk), in which case the requirement values shown in table 2 are acceptable. In general terms, the latest (1996) values are lower than those in 1985. The latest values are based on observation of intakes of infants in relationship to growth, in addition to nitrogen balance studies.

It is important to realize that these requirements do not take into account illness nor the amounts required to recover from weight loss. Any form of stress (including infection and trauma) increases urinary nitrogen excretion and hence increases protein needs by amounts of 20 to 30% ⁵Having recovered from the acute illness the child will then need to restore the lost lean mass (catch up) as well as normal growth. In those cases, the child will need to take more protein and for that matter energy. How much more depends upon the rate of weight gain and the reader is referred to the supplement to the European Journal of Clinical Nutrition ⁵for full details. However it may require an increase of up to 50% over the values listed in table 2. In practice, the protein content of a mixed diet, is between 10 to 15% of energy, as a child eats more food, to meet their energy needs they will also meet their protein requirements.

The implications of these new estimates is principally with regard to energy needs in the first two months of life. The values shown in the energy requirement tables are mean values. It is important for the clinician to bear in mind that there is a co-efficient variance of 10 - 15% around these mean values to cover the range of individual needs. Thus, although you may counsel the parents/ caregiver to feed at around 110 kcal/ kg., some more rapidly growing infants might need more. At a practical clinical level, the protein needs would not alter anything in feeding practice. With hospitalized children, requiring nutritional support, the basal values need to be considered. However, as mentioned above, children who are undergoing stress or illness, will need additional energy and protein. Their review ^2,5suggest that they can be increased by 20 to 50%; the lower values relating to stress and illness and the higher values relating to recovery from undernutriton, particularly during the period of catch-up growth.

References:

1. Report of a Joint FAO/WHO/UNU Expert Consultation. World health Organization, Geneva. Technical Report Series #724, 1985.

2. Scrimshaw NS, Waterlow JC, Schurch B. (eds) Energy and Protein Requirements. Eur. J.Clin. Nutr. Feb.1996, 50: Suppl 1.

3. Butte NF. Energy requirements of infants.Eur J Clin Nutr 1996, 50, Suppl 1: S24-S36.

4. Schoeller DA. Measurement of energy expenditure in free-living humans using doubly labeled water. J. Nutr. , 1988,118:1278-89.

5 Torun B, Davies PSW, Livingstone MBE, Paolisso M, Spurr GB. Energy requirements and dietary energy recommendations for children and adolescents 1 to 18 years old. Eur J Clin Nutr 1996, 50, Suppl 1:S37-S81, .

6. Dewey KG, Beaton G, Fjed C, Lonnerdal B, Reeds P. Protein requirements of infants and children. Eur J Clin Nutr, 1996, Suppl 1: S119-S150, .

Table 1:

Energy Requirements of Infants 0-2 year old

(World Health Organization 1985 versus 1996 estimates)

*The 1996 energy requirement is calculated from total energy expenditure taking into account energy absorption of 85% of under 4 months and 90% of intake 4 - 12 months.

Table 2:

Protein Requirements of Infants 0-2 year old

(World Health Organization 1985 vs. 1996 estimates)