J Karlberg, K Albertsson-Wikland

In order to measure obesity or under nutrition through body measurements the optimum weight for height index should be independent (not correlated) with height. Common expressions of weight for height such as body mass index (BMI) is, however correlated with height; a taller child will have a higher BMI. The aim of this work was to develop a nutritional status index being independent of height.

The data used here to illustrate a new weight for height index represents a longitudinal growth study of 3650 full-term, healthy children born in 1973-1975 in Gothenburg, Sweden.

The new nutritional status index was taken from the linear regression between weight standard deviation scores (SDS) and height SDS, or weight_SDS-β *height_SDS (W_SDSβ*H_SDS), where β is the slope between weight SDS and height SDS. After correcting weight SDS for the slope (β approximately 0.7 for most ages) of this linear regression the correlation coefficient between the new index and height became zero for all ages.

BMI (W/H²) and other similar expressions are correlated with height and should not be used to measure neither obesity nor under nutrition. The alternative method presented here (W_SDS-β*H_SDS) has also a practical advantage, i.e. by offering a quick way of estimating the individual weight for height; weight_SDS and height_SDS are read from the individual growth chart and W_SDS-0.7*H_SDS is computed.