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4. Protein needs during catch-up growth

4.1. Basis of recommendations in the 1985 report

In the 1985 report (p. 143), protein requirements for catch-up growth were considered separately according to whether children were low in weight-for-height (wasted) or low in height-for-age (stunted). In the case of wasting, protein needs were estimated to be 0.23 g per gram of tissue deposited (assuming that 16% of tissue deposited is protein, and that the efficiency of conversion of dietary protein to tissue protein is 70%: 0.16/ 0.70 = 0.23). However, this estimate was not used in a factorial model to calculate total requirements. In the case of stunted children, examples of how protein needs might be calculated based on the 'safe' levels of intake for normal children were illustrated (Table 52 in the 1985 report). The approach proposed was to estimate average requirement for catch-up by using the 'safe level' for a child of the same height-age (not chronological age) and at the median weight for height. The 1985 report defended this approach on the basis that it provided estimates that were consistent with observed rates of catch-up growth.

4.2. Protein and energy needs for rapid catch-up growth

In the 1985 report, an example was given for catch-up growth of an undernourished child with a weight deficit of 3.3-3.8 kg and a height-age of 12 months, provided with a protein intake of 1.37 g/kg/d (p. 198). It was calculated that with this level of intake, satisfactory catch-up would require 5-6 months. However, for hospitalized malnourished children, such a long duration of recovery is impractical. Furthermore, it is likely that during this period there would be illnesses causing additional catabolic losses. Hastening catch-up growth would be advantageous, if it could be achieved by practical nutritional measures.

To test the hypothesis that catch-up growth could be more rapid without compromising body composition or other indices of nutritional recovery, Fjeld et al (1989a) refed marasmic children using diets formulated to meet the theoretical requirements for energy, protein and micronutrients. Children were randomly assigned to dietary treatments that permitted either moderate (4-6 g/kg/d) or rapid (12-16g/kg/d) rates of weight gain. The composition of total weight gained and final body composition were similar in the two groups, indicating that appropriate nutritional therapy can reduce the time required for catch-up growth while restoring reference levels of body composition.

In the above study, the rate of weight gain in the rapid gain group (12-16g/kg/d) was well within the range of growth velocity observed in other studies in hospital settings (up to 20 g/kg/d: Waterlow, 1992a). This rate of growth is far above the average growth velocity for a normal young child (approximately 1.3 g/kg/d at 6-12 months). Such a high rate of catch-up growth cannot be expected with dietary interventions in community settings, in which few children would be likely to have more than mild to moderate growth impairment (compared with the severe cases treated in a clinical setting). However, a report from The Gambia describes rates of catch-up growth of up to eight times the average daily growth rate calculated from the normal annual growth increment (Rowland et al, 1977).

In the 1985 report (p. 147), the percentage increase in protein requirements for children to grow at twice the 'normal' growth rate was presented as an example of what might be applicable in the community. Although there is clearly a need for more information on rates of catch-up growth in non-hospital settings, the 'twice normal' example given in the 1985 report is almost certainly well below the potential, given appropriate dietary interventions.

For a stunted child with normal body composition, the amount of protein required for rapid catch-up growth can be estimated based on the gain in lean tissue associated with normal growth. In such cases, protein makes up approximately 16-17% of weight gain. Nitrogen balance data from recovering malnourished children (Waterlow, 1992a; Fjeld et al, 1989a) and reference values for normal children at 9-12 months of age (Fomon et al, 1982) are consistent with this estimate. For severely wasted children, catch-up growth will likely include a higher proportion of fat tissue, and therefore a proportionately lower amount of lean tissue. Table 21 provides estimates of the protein and energy needs at various rates of weight gain under conditions of either normal growth (i.e. applicable to the stunted child), or a high rate of fat deposition (i.e. applicable to the severely wasted child). In the latter case, the estimates of fat and lean tissue gain were taken from those expected of a normal infant at 2-3 months of age, when fat deposition is rapid (Fomon et al, 1982); the assumed percentage of fat tissue (43%) is consistent with data for recovering marasmic children in Peru (Fjeld et al, 1989a). In both parts of Table 21, the maintenance protein need was assumed to be 0.63 g/kg/d (90 mg N/ kg/d). The efficiency of conversion of dietary protein to tissue protein was estimated at 70%, to be consistent with the factorial models presented in previous sections. It is possible, however, that recovering malnourished children are more efficient at protein deposition. Table 21 presents energy needs based on two levels of 'maintenance' energy expenditure (i.e. including BMR and activity but not growth): 80 and 90 kcal/kg/d. The latter value is typical of normal infants at 9-12 months of age (see the position paper by Butte), but may be higher than would be expected of malnourished infants if they are less active. The former value (80 kcal/kg/d) is similar to the average energy expenditure of preschool children (see the position paper by Torun et al) and to energy expenditure for maintenance and activity of recovering malnourished children in Peru (Fjeld et al, 1989b). The table also presents the ratios of requirements expressed as percentage of energy from protein (P: E) in each situation.

Several points are noteworthy with regard to the estimates in Table 21:

(1) At the higher rates of catch-up growth (10-20g/kg/ d), the amount of protein needed ranges from 2.0 to 5.4 g/kg/d, depending on the composition of weight gain. The P: E ratio is much higher for children expected to have a normal composition of weight gain (up to 15% dietary protein) than for those expected to have a high rate of fat deposition (up to 7% dietary protein). Because most wasted children are also stunted, it is probably prudent to err on the high side when calculating the P: E ratio for refeeding, especially given the fact that the P: E ratios in Table 21 are based on average estimated requirements, and are therefore not analogous to 'safe levels'.

(2) Energy needs are higher for wasted children than for non-wasted children, because of the higher energy cost of depositing fat tissue. At the higher rates of weight gain, energy needs range from 113 to 156 kcal/kg/d for nonwasted children and from 140 to 210 kcal/kg/d for wasted children. The duration of such feeding regimes should be determined on a case-by-case basis; if an initially wasted child is fed a very high energy diet for too long, he or she may become obese.

Table 21 Protein and energy needs for catch-up growth at different rates of weight gain

^a 17% protein, 9% fat; assume energy cost of growth = 3.3 kcal/g (based on 5.65 kcal/g protein and 9.25 kcal/g fat, with efficiencies of synthesis of 42% and 85%, respectively (Roberts and Young, 1988): 0.17g protein × 5.65 kcal/g/0.42 = 2.3 kcal; 0.09g fat × 9.25 kcal/g/0.85 = 1.0 kcal); protein needs for growth = protein need/efficiency = 0.17/0.7 = 0.24 g/kg/d.
^b 10% protein, 43% fat; assume energy cost of growth = 6.0 kcal/g (based on 5.65 kcal/g protein and 9.25 kcal/g fat, with efficiencies of synthesis of 42% and 85%, respectively (Roberts and Young, 1988): 0.10 g protein × 5.65 kcal/g/0.42 = 1.3 kcal; 0.43 g fat × 9.25 kcal/g/0.85 = 4.7 kcal); protein needs for growth = protein need/efficiency = 0.10/0.7 = 0.14g/kg/d.
^c EE = energy expenditure for maintenance and activity.
^d In normal children, average rates of weight gain are about 1.3 g kg/d at 6-12 months, 0.8 g/kg/d at 12-18 months and O.5 g/kg/d at 18-24 months.
^e Assume maintenance needs for protein of 0.63 g/kg/d.
^f Metabolizable energy intake.
^g Ratio of requirements expressed as percentage of energy from protein. This differs from the concept of a 'sale level' of P: E as used in Section 2.4.

Waterlow (1992a) noted that requirements based only on gains in tissue protein do not account for restoration of proteins that may be depleted in malnourished children, such as serum albumin. However, he calculated that the amount of protein required for this is only about 5% of the tissue protein deficit, which is too small to strongly affect the estimates in Table 21. Waterlow (1992a) also illustrated the impact of illnesses during the period of recovery on protein needs for catch-up growth, using the assumptions that each day of infection produces a deficit of 30 g in weight gain and that the extra protein is consumed only during the days when the child is well. For a recovery period of 100 days, protein needs for catch-up increase by about 15-25% when the prevalence of infections is 20-30%. The impact of infections is discussed in more detail in section 5.

For a stunted child with normal body composition, the rate of catch-up growth may be limited by the amount of time needed to recover in height. It has been observed that when recovering malnourished children reach a normal weight for height, their appetite and rate of weight gain usually diminish, even though they may still be stunted. Thus, in these situations it would be rare to observe rates of weight gain as high as the upper end of the range in Table 21 (20 g/kg/d). A more realistic example is shown in Table 22, which provides estimates of the protein and energy needs for a child whose initial height-for-age is three standard deviations below the reference median and who reaches normal height-forage within 6 months. Weight gain in this case is expected to be 1.63 g/kg/d. At this rate, energy needs are only about 4% higher than normal, whereas protein needs are 37% greater than the requirement for a normal child. Table 22 is meant to provide only an example of the needs for catch-up in height, and is not intended to be used prescriptively.

Table 22 Example of protein and energy needs for catch-up in height

N = normal boy, 2 years of age, initial Z-score in height = 0.
S = stunted boy, 2 years of age, initial Z-score in height = - 3, but weight-for-height normal.
Assuming full catch-up in height in 6 months (with normal body composition)

4.3. Evidence from nutrition intervention studies

Results of nutrition interventions in developing countries appear to provide support for the value of relatively high protein intakes for malnourished children (Kabir et al, 1992, 1993; Fjeld et al, 1989a; Malcolm, 1970; Jackson et al, 1990). Unfortunately, most studies have not controlled for the levels of micronutrients provided by the supplementary foods given, so it is difficult to determine whether the observed improvement in growth can be attributed to extra protein or to higher intakes of other nutrients. For example, Kabir et al (1992, 1993) demonstrated that catch-up growth can be accelerated in children 2-4 y of age recovering from malnutrition secondary to shigellosis. Accelerated linear growth was achieved by supplementing the standard recovery diet (lentils, banana, bread, rice, oil, milk powder, sugar) with egg, milk and chicken. The standard diet provided 7.5% of dietary energy as protein, whereas the experimental diet provided 15% of energy as protein, as well as increased levels of other nutrients. The linear growth rate in control children was comparable with the NCHS reference; the rate in the experimental group was significantly higher. In the study of malnourished Peruvian children by Fjeld et al (1989a), height gain in the control children fed the standard recovery diet (approximately 125 kcal/kg/d, 8% energy as protein, micronutrient intake supplemented by level of energy intake) was comparable to the NCHS reference based on height-age, whereas height gain in the children fed the experimental diet (approximately 165 kcal/kg/d, 11 % energy as protein, micronutrient intake supplemented by level of energy intake) was significantly greater than the NCHS reference based on height-age. In several studies, children fed control diets (considered adequate for children not experiencing catch-up growth, but having less protein and other nutrients than the experimental diets) tended to deposit fat tissue at the expense of lean tissue (Malcolm, 1970; MacLean and Graham, 1980; Jackson et al, 1990; Fjeld et al, 1989), which supports the idea that restoration of appropriate body composition requires nutrient intakes different from those needed at lower rates of weight gain.

The mechanism by which dietary treatment stimulates linear growth probably involves increased synthesis of insulin-like growth factor I (IGF-I) and IGF-binding proteins (Kabir et al, 1992; Kabir et al, 1993). The above studies suggest that dietary interventions can stimulate the anabolic drive during convalescence from malnutrition, which implies that nutrient requirements during this period should be calculated on the basis of the maximal rate of growth achievable without compromising optimal body composition or function. It is important to note that the increased needs for catch-up growth include not only protein and energy but nearly all other nutrients as well.

At present there is some disagreement about whether complete catch-up growth in height of stunted children is achievable after the first 2-3 years of life (Uauy & Alvear et al, 1992; Waterlow, 1992a; Martorell et al, 1994; Golden, 1994). If there is a 'critical period' for linear catch-up growth, the benefits of increased nutrient intake to support accelerated growth may not be demonstrable in older children.

4.4. Recommendations for revision of the 1985 report

Requirements for catch-up growth should include a factor for maintenance and a factor for growth. The latter should be presented for various rates of weight gain, as illustrated in Table 21. The values used for maintenance nitrogen needs and the efficiency of conversion from dietary protein to body protein should be consistent with those chosen for the protein requirement tables for infants and children in general.

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