What do we learn from comparing ethnic-specific and WHO child growth references?

There is an ongoing discussion as to the question of which childhood growth references to use for which population. The WHO child growth standard (0–5 years) was designed as a universal norm, because WHO concluded that growth of affluent children between birth and 5 years of age was found to be quite similar on all continents. Despite it being implemented in over 125 countries, including a complementary reference for 5–19-year-olds, the universal application of both the standard and the reference for assessing growth of children has been questioned repeatedly, especially its use in Asian populations. In this issue of Public Health Nutrition, Sandjaja et al. contribute to the discussion with their South-East Asian Nutrition Surveys (SEANUTS) study of weight and BMI in children from four South-East Asian countries (Malaysia, Thailand, Indonesia and Vietnam). They derived population-specific weight-for-age and BMI-for-age reference values from their pooled data from these four countries. They recommend using these reference values in clinical practice as well as for research and public health applications, as an additional tool to the WHO reference values, and instead of country-specific values. As swapping references may have a profound impact on the detection of children at risk, such a recommendation needs thorough investigation and discussion. Sandjaja et al.’s article is an illustration of the difficult questions we are confronted with in the area of something seemingly as simple as optimal height and weight of children. For several reasons these questions are difficult. First, growth is influenced by genetic, epigenetic, lifestyle and environmental factors, and we do not exactly know the impact of each type of factor on a global scale nor in specific populations. Second, regarding weight and BMI as estimators of fat mass, we know that these quantities do not differentiate between fat and lean body mass. In addition, secular changes in height may represent a third difficulty. However, a disturbing influence of height on BMI reference values is likely limited. Therefore, we do not deal with this subject here. First, we discuss the problem of using weight or BMI as an estimator of fat mass. It is currently well known that the body composition of Asian people differs from Caucasians. For any given BMI (or weight), Asian populations generally have a larger fat mass together with a smaller muscle mass than Caucasian populations. This is found in all age groups and even at birth; a well-known example is the so-called ‘thin-fat’ Indian baby with low birth weight and high fat mass. In Sri Lankan children, even in those considered thin, the fat mass was much higher than in Caucasian children. These studies stress the problem of using a single measure of body size (weight or BMI), not differentiating between fat and lean body mass. This is especially true when universally applicable growth standards such as those of WHO are used. In several cases, country-specific or national BMI-for-age references were shown to be superior in detecting an excess of body fat compared with universal references and may therefore be more appropriate for use in clinical practice. We now use our own studies on growth of South Asian children in the Hague, the Netherlands, as an example of the problems one encounters because of the complexity of the factors influencing growth. In our ‘1976 study’ of South Asian children living in the Netherlands, we developed reference values based on data from South Asian children born in 1974–1976, living in affluent circumstances but before the obesity epidemic started. We found a left shift in the ethnic-specific BMI reference, compared with the WHO reference. As a result, many children with underweight according to the WHO reference actually had a normal weight when based on ethnic-specific norms. And at the other end of the BMI spectrum, many children now had overweight, although they had a normal weight according to the universal standard. So, on the one hand, parents might have been wrongly informed to stimulate their child to eat more; and, on the other, parents might have been wrongly reassured that their child had a normal weight. Some years after developing these South Asianspecific reference values, we studied growth in South Asian children 0–19 years of age. In that cross-sectional study, performed in 2007–2010, children with a high BMI were over-represented in 5–19-year-olds, compared with the distribution of the South Asian-specific reference from the ‘1976 study’ and even compared with the WHO reference. Apparently, these results reflected the effects of the obesity epidemic. So, if we would have used a reference based on more recently acquired data, we would have underestimated overweight and obesity prevalence figures in this group. Actually, our estimation would have been even worse than an estimation based on the universal standard. So, a first conclusion from our studies would be that the requirement of restriction to children Public Health Nutrition: 21(16), 2969–2971 doi:10.1017/S1368980018002252