Science Selection September 2017 | Volume 125 | Issue 9
Estimated Deficiencies Resulting from Reduced Protein Content of Staple Foods: Taking the Cream out of the Crop?
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Published: 22 September 2017
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Related EHP Article
Estimated Effects of Future Atmospheric CO2 Concentrations on Protein Intake and the Risk of Protein Deficiency by Country and Region
Projected changes in climate are expected to play a complicated role in global crop production. Rising levels of atmospheric carbon dioxide (CO2) may improve yield, but higher average temperatures and more frequent extreme weather could damage crops, increase the risk of foodborne illness, and impair distribution of safe and nutritious food.1 However, there is another, less intuitive potential effect on the global food supply and human nutrition that also warrants consideration: reductions in the nutrient content of food staples eaten around the world.2 A new study in Environmental Health Perspectives presents an early estimate of impacts due to changes in one of these nutrients, protein.3
As levels of atmospheric CO2 rise, concentrations of protein4,5 and essential minerals such as calcium, magnesium, zinc, and iron4,6,7,8 decline in most vascular plants, particularly those plants that utilize what is known as C3 photosynthesis. C3 plants respond to increased concentrations of atmospheric CO2 more vigorously than C4 plants. C3 plants represent most of the Earth’s plant cover9 and include staples such as rice, wheat, barley, and potatoes.10
Consequences for public health are difficult to predict and depend on a range of variables, including local diet and farming practices. “The two effects [increased production and decreased nutrient content] come as a set, so there will be those who benefit and those who are harmed by these changes, depending on many factors,” says Justin McGrath, a postdoctoral research associate at the University of Illinois Urbana-Champaign, who was not involved in the current study.
By analyzing regional diets worldwide and modeling likely changes to protein content triggered by elevated levels of CO2, the authors of the new study estimate that by the year 2050 more than 148 million people could become newly at risk for protein deficiency.3 “What this work shows, as well as a lot of other research, is that anthropogenic disruptions of most of Earth’s natural systems have significant impacts on global health,” says senior author Samuel Myers of Harvard University. Myers is working to synthesize existing research on CO2 and human nutrition in hopes of raising awareness of this potential problem among researchers and the public.
Protein intake and socioeconomic status are closely linked, says lead author and former Harvard research fellow Danielle Medek, and current disparities are likely to be exacerbated by climate change. “The people with the most impoverished diets within a country are most likely to lack animal sources of protein and therefore likely to be disproportionately affected [by reduced intake of protein from plants],” she says. Medek and colleagues estimate, based on data from the Food and Agriculture Organization of the United Nations,11 that 82% of the world’s population currently derives most of its daily protein from plants.11
The stimulated carbohydrate production and plant growth induced by higher levels of atmospheric CO2 can itself lead to comparatively lower nutrient concentrations in plants, McGrath explains. Although researchers do not fully understand all the mechanisms involved, one contributor to this imbalance appears to be simple dilution. “You have got more carbohydrates, which dilute everything else,” he says. In addition, he says, “There is evidence that affected plants may take up less of some, but not all, nutrients from the soil.”6
However, the increase in carbohydrate concentration may be the main driver of health effects associated with the phenomenon, says Irakli Loladze, a professor at Bryan College of Health Sciences. “It is like sprinkling every portion of plant-based foods with sugar,” he says. Loladze, who was one of the first to call attention to the link between CO2 and the quality of human nutrition,8 was not involved in the current study.
In order to estimate risk, the researchers compared projected daily intake of protein against the U.S. Institute of Medicine’s nutrient reference values.12 But as Medek points out, health effects may also occur among those whose projected protein intake falls just shy of the threshold, and among the 1.4 billion people around the world thought to already be at risk of protein deficiency.
Daniel Taub, a professor of biology at Southwestern University, says he is wary of the idea of predicting declines in plant protein attributable to rising atmospheric CO2. “The extent to which carbon dioxide affects protein concentration depends on a lot of different things,” he says, many of which are unpredictable and subject to human modification, such as nitrogen levels in the soil and specific cultivars planted. “The real-world effect under real agricultural conditions will always be variable and impossible to predict with precision and accuracy,” he says.
He does not, however, dispute the study’s core finding that impacts will be concentrated in poorer, rapidly populating regions where people rely on C3 plants for protein. India alone—with its high consumption of rice and wheat coupled with its large and rapidly increasing population13—accounts for more than one-third of the individuals predicted by the study to be put newly at risk of protein deficiency.3
“In a qualitative way, what the authors are saying is that India is a place to look out for. Absolutely, no question, they are among the people I would look out for,” Taub says. But he adds that people in Bangladesh, Vietnam, Cambodia, and central Asian countries such as Azerbaijan and Tajikistan derive an even higher percentage of their calories from C3 grains. “All of these countries,” he says, “may face real challenges with this in the future.”
Nate Seltenrich covers science and the environment from Petaluma, California. His work has appeared in High Country News, Sierra, Yale Environment 360, Earth Island Journal, and other regional and national publications.
1. Ziska L, Crimmins A, Auclair A, DeGrasse S, Garofalo JF, Khan AS, et al. 2016. Chapter 7: food safety, nutrition, and distribution. In: The Impacts of Climate Change on Human Health in the United States: A Scientific Assessment. Crimmins A, Balbus J, Gamble JL, Beard CB, Bell JE, Dodgen D, et al., eds. Washington, DC:U.S. Global Change Research Program, 189–216. https://doi.org/10.7930/J0ZP4417 [accessed 10 March 2017].
2. Poorter H, van Berkel Y, Baxter R, den Hertog J, Dijkstra P, Gifford RM, et al. 1997. The effect of elevated CO2 on the chemical composition and construction costs of leaves of 27 C3 species. Plant Cell Environ 20(4):472–482, https://doi.org/10.1046/j.1365-3040.1997.d01-84.x.
3. Medek DE, Schwartz J, Myers SS. 2017. Estimated effects of future atmospheric CO2 concentrations on protein intake and the risk of protein deficiency by country and region. Environ Health Perspect 125(8):087002, https://doi.org/10.1289/EHP41.
4. Myers SS, Wessells KR, Kloog I, Zanobetti A, Schwartz J. 2015. Effect of increased concentrations of atmospheric carbon dioxide on the global threat of zinc deficiency: a modelling study. Lancet Glob Health 3(10):e639–e645, PMID: 26189102, https://doi.org/10.1016/S2214-109X(15)00093-5.
5. Taub DR, Miller B, Allen H. 2008. Effects of elevated CO2 on the protein concentration of food crops: a meta-analysis. Glob Chang Biol 14(3):565–575, https://doi.org/10.1111/j.1365-2486.2007.01511.x.
6. Myers SS, Zanobetti A, Kloog I, Huybers P, Leakey ADB, Bloom AJ, et al. 2014. Increasing CO2 threatens human nutrition. Nature 510(7503):139–142, PMID: 24805231, https://doi.org/10.1038/nature13179.
8. Loladze I. 2002. Rising atmospheric CO2 and human nutrition: toward globally imbalanced plant stoichiometry? Trends Ecol Evol 17(10):457–461, https://doi.org/10.1016/S0169-5347(02)02587-9.
9. Still CJ, Berry JA, Collatz GJ, DeFries RS. 2003. Global distribution of C3 and C4 vegetation: carbon cycle implications. Global Biogeochem Cycles 17(1):1006, https://doi.org/10.1029/2001GB001807.
10. Georgia State University. C3 Photosynthesis [website]. http://hyperphysics.phy-astr.gsu.edu/hbase/Biology/phoc.html [accessed 10 March 2017].
11. Food and Agriculture Organization of the United Nations. 2017. Food Balance Sheets, 1970–2011 [website]. http://faostat3.fao.org [accessed 6 July 2017].
12. National Academy of Sciences. 2016. Dietary Reference Intakes Tables and Application [website]. http://www.nationalacademies.org/hmd/Activities/Nutrition/SummaryDRIs/DRI-Tables.aspx [accessed 10 March 2017].
13. United Nations. 2017. 2017 Revision of World Population Prospects [website]. https://esa.un.org/unpd/wpp/ [accessed 6 July 2017].