Stunting is defined as being at least 2 standard deviations (SD) below the average of the reference group for your height, sex and age. Wasting is defined as being at least 2 SD below average weight for your height and sex. The reference group is an international sample of socio-economically advantaged breast fed children.
Commenter “Someguy” pointed out that using stunting rates to measure how malnourished a certain ethnic group was is faulty because some groups might be genetically shorter than others. I agree but was unsure if this genetic difference would show up in young children. After all, the World Health Organization (WHO) claims children of all ethnic groups grow similarly when breast fed and born and raised healthy, at least up to age five, and so a single reference group can be applied internationally.
Further, Arthur Jensen stated that (in his population) height has a heritability of 0.95 in early adulthood, but only 0.30 in infancy. With genes having only moderate effects in the first years of life, this made it seem quite plausible that all races (with the exception of pygmies) could use the same growth chart to measure nutritional status.
However even comparing different races in First World countries show large differences in early childhood height. For example averaging across ages zero, 0.5, 1.5, 2.5, 3.5 and 4.5 years, Dutch boys (see table 1) are 1.02 SD taller than Japanese boys (Japanese SD used since the Dutch one not provided).
To be sure this is much smaller than the 1.93 SD height gap that shows up at age 17.5, consistent with the square root of height heritability being almost twice as high in early adulthood compared to infancy.
It is sometimes said that in most ethnic groups, well nourished kids are within half an SD of the WHO growth chart so close enough, but if one population is half an SD above and another half an SD below, that’s a 1 SD difference!
And because small differences in the mean create huge differences at the extremes, a 1 SD gap means the shorter group will show about 7% of their population stunting while the taller group will show only 0.6% despite the fact that both groups have equal nutrition! That’s a little too much error for comfort.
If the World Health Organization is serious about measuring malnutrition, they should invest in getting us better polygenic scores for height. Only then could they say with accuracy that a given population is below their genetic height potential, and thus malnourished.