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Seasonal variation in growth rate of weight of 4,030 Ntomba babies (Lake Tumba, Zaire), aged 0 to 4 years was analysed in relation to sex, age and caste differences. The data were collected between mid‐August, 1977, and May, 1980, during a longitudinal survey and consisted of 34,470 measurements of body weight. The actual analysis is based on mean standardized weight increments, calculated over three monthly intervals.
The growth rate in weight of Ntomba babies showed a cyclic pattern, which appeared to be synchronized with the alternations of dry and rainy seasons. The unfavourable rainy seasons decelerated growth in weight to about 0.2 SD below the average rate. (This is approximately 40 g/month below the average velocity). The subsequent favourable dry seasons resulted in a catch‐up growth. The effects were visible towards the end of each season or in the beginning of the next season and were more pronounced and lasted longer when following the major rainy or dry seasons than when following the minor rainy or dry seasons. The Twa (pygmies) showed a similar, but slightly more contrasting, annual pattern in growth rate compared with the (tall) Oto. Girls also tended to show somewhat sharper contrasts between maximum and minimum growth velocities when compared to boys, but, at the same time, they seemed to catch‐up more quickly. The analysis of periodicity in growth rate of weight in four different age groups, corresponding to characteristic periods of lactation and weaning, revealed a seasonality in the annual pattern of growth velocity in weight for children in all age groups, including those exclusively on breast‐feeding. It was postulated that the growth of breast‐fed babies was influenced by changes in the composition and volume of the milk secretion, which was itself subject to seasonal variations in the mothers’ diet.