Men from wealthy countries are getting taller because their diet is rich in nitrogen and phosphorus
18 de December 2017
Mean male height in countries with a high level of GDP is 23 cm greater than in countries with a low level, a difference that has risen by 1.5 cm over the last 30 years. Thanks to a more varied diet rich in animal products, the annual nitrogen and phosphorus intake of people in wealthy countries is practically twice that of those in poor countries.
A CREAF-led study published in Scientific Reports has concluded that the growing difference in height between men from rich and poor countries is related to the amount of nitrogen and phosphorus in their diet. This finding is based on data from institutions such as the Food and Agriculture Organization (FAO) of the United Nations on men from 80 countries who were born in the 1960s, 1970s or 1980s (for the study’s purposes, the FAO only had useful data on young male adults).
The study has shown that mean male height varies substantially between countries, and that this variation is connected to each country’s gross domestic product (GDP). On average, there is a difference of 23 cm between the countries with the tallest inhabitants (Denmark and the Netherlands, with a mean height of 1.83 m) and those with the shortest (Guatemala and Vietnam, with a mean height of 1.60 m). The difference in height between people from rich and poor countries (based on GDP) has actually risen by 1.5 cm in the last 30 years, as the former have become taller while the latter have not.
The study has also demonstrated that the height difference in question is much more closely linked to per capita nitrogen and phosphorus intake than to other factors that might seem more relevant, such as daily calorie intake. Rich countries’ inhabitants obtain more nitrogen and phosphorus through their diet each year (19.5 kg and 2.17 kg respectively) than the inhabitants of poor countries do (9.66 kg and 1.35 kg respectively). Furthermore, between 1961 and 2009 nitrogen intake rose by 12% in high GDP countries but by just 7% in low GDP countries (the equivalent difference in the case of phosphorus was only 1%).
In comparison to that of people from poor countries, the study explains, the diet of people born in high GDP countries is more varied and has a higher animal to plant product ratio. Rich countries’ inhabitants consequently obtain larger quantities of nitrogen and phosphorus, as well as having a higher nitrogen to phosphorus ratio. Additionally, the plant products they consume are of better quality and thus contain more of the nutrients in question.
A food security problem with no easy solution
“Height isn’t a neutral trait, as science has proven it to be directly related to health and life expectancy”, says CREAF researcher and study co-author Jordi Sardans. “So, if we want to do away with both height and health-related differences between rich and poor countries, we need to think about the quantities of nitrogen and phosphorus people get from food, and suggest major changes to our agricultural model and the proportion of animal products we eat in relation to plant products on a global scale.”
According to Sardans, a combination of two complementary measures could put an end to this flagrant inequality between rich and poor countries without any detriment to the former. Firstly, bearing in mind that it takes an average of 10 g of plant-based food to produce 1 g of animal product, it would be very positive if wealthy countries were to take steps to adopt a diet less rich in animal products and richer in plant products in appropriate proportions. That would contribute to increasing food production worldwide and making more animal products, more nutritious plant products and a more varied diet available to poor countries. Secondly, as the CREAF-based CSIC research professor Josep Peñuelas explains, attempts to improve poor countries’ crop productivity must take the shortage of phosphorus into account. “Crop productivity is better when phosphorus levels in the soil are high, but the soil in tropical areas, where many of the poorest countries lie, contains very little phosphorus”, he says. “Furthermore, as global phosphorus reserves are limited and located in just a few parts of the world, there is a clear situation of speculation and constant price rises, making fertilizers containing phosphorus unaffordable for farmers in poor countries”, he adds. “So, everything unfortunately seems to suggest that the differences in quality and quantity between the diets of rich and poor countries will continue to grow”, he concludes.
Peñuelas J., Janssens I.A., Ciais P., Obersteiner M., Krisztin T., Piao S., Sardans J. (2017) Increasing gap in human height between rich and poor countries associated to their different intakes of N and P. Nature Scientific Reports 7, 17671. DOI: 10.1038/s41598-017-17880-3