Photo: AFP
There is one country that constantly produces the tallest people in the world - so what is their secret?
Like in the rest of Europe and Western nations, heights in the Netherlands have increased dramatically over the past 200 years - but for some reason, the Dutch grow higher.
The Dutch started shooting up in the late 19th century, Kristina Thompson, an associate professor of health and society at Wageningen University, told RNZ's Nights.
"At the beginning of the 19th century, the Dutch were relatively short - they were around 163-165 centimetres for men. And we really start to see a massive shift towards the middle of the 19th century when the Dutch start growing at this tremendous rate.
"And it was only really in the 20th century that the Dutch outstripped other nations and became the tallest nation in the world."
This is not a story of genetics, she said.
"This change really happened way too fast for genetics to be the main story here. And unfortunately, in terms of the type of environmental factors, we don't have a perfect, neat and tidy answer just yet.
"But we have identified a bunch of contributing factors that likely played a role. And that all likely went just slightly better in the Netherlands than in other countries."
Body height is a reflection of a concept called net nutrition, she said. The quality and quantity of food someone eats, minus different stresses on their bodies.
"These stressors are disease, physical labour, and actual stress. So sometimes someone can be eating plenty to reach their genetic potential height, but energy might be diverted to other sources.
"In the Netherlands, the main story here is protein - that's the most important thing for growth. And the Netherlands had that a lot more than in other countries."
The Dutch have a long tradition of dairy, and that protein source is a big part of the explanation for their height, she said.
"There are so many dairy cows in the Netherlands and people consume a whole lot of dairy. And even within the Netherlands, there's this strong relationship between the number of dairy cows per municipality and how tall people were."
The Dutch were also consuming more high quality animal protein than their neighbours, she said.
"The Dutch are the second-biggest potato eaters in the world after the Irish, and there is an association between eating potatoes and being slightly taller. They're just a bit more nutrient dense than other types of staple carbs."
And it was not just a story about diet - the Dutch have done well with controlling disease in their population, she said.
"The Dutch just were a little bit more more proactive there. There was a lot of infectious disease here, particularly in the 19th century, but the Dutch did not have as many big cities in the same period.
"And they also didn't industrialise until really, really late. So they missed out on a lot of the sort of worst aspects of being in crowded, unsanitary spaces. And they also started public works projects earlier in terms of public sanitation. So, there were lower rates of waterborne diseases a bit earlier than in other countries."
So, given the Dutch stand taller than other nations, were they likely to keep growing into a nation of giants? Not so much, she said.
"The opposite is happening; the Dutch are currently shrinking, or average heights are decreasing. Children today are shorter than their parents - in particular, daughters are shorter than their mothers."
A number of theories sought to explain this shrinking - more vegans and vegetarians was one explanation.
"I don't quite buy that. I think, really, you need a slightly bigger, more systemic explanation for that. What we know is that the Dutch are getting heavier - like many high-income countries - and particularly children are getting heavier at younger ages.
"And for girls, this might be particularly problematic because higher body fat percentages can sort of trick the body into thinking it's mature, so that girls reach menarche or have their first menstruation at younger ages."
Women in the 1960s and 1970s would reach maturity around age 16. Now it was closer to age 12, she said.
"Girls stop growing when that happens. And this would ultimately result in shorter heights. And this is just a theory of mine. I've run it past a few people who think this is sensible, but it's something I would like to investigate."
