Average reduction in grain protein at elevated relative to ambient CO2 for 18 cultivated rice lines of contrasting genetic backgrounds grown in China and Japan using FACE technology. Graphic: Zhu, et al., 2018 / Science Advances

By Elena Suglia
10 December 2018

(Scientific American) – Is it possible to starve yourself of nutrients while simultaneously gaining weight? It turns out the answer is yes. According to a growing body of research, rising carbon dioxide levels are making our food less nutritious, robbing key crops of vitamins essential to human development.

Studies have shown that crops as varied as wheat, maize, soybeans and field peas contain less protein, zinc, and iron when grown under levels of carbon dioxide expected by 2050. Many crops have already suffered losses in these nutrients; one study compared modern plants with historical herbarium specimens and found that levels of all minerals, including zinc, iron, and calcium, closely tracked carbon dioxide levels through time.

The latest paper on the topic, published earlier this year in Science Advances, found that concentrations of essential nutrients decreased in 18 strains of rice after being exposed to increased carbon dioxide levels in an experiment. The study was the first to show that B vitamins like riboflavin, which helps your body break down food to make energy, and folate, which is important for fetal development, dropped by as much as 30 percent.

It seems counterintuitive that more carbon dioxide could harm plants, since it is one of the main ingredients that plants use to grow, but it turns out that too much carbon dioxide is as unhealthy for plants as too many carbohydrates are for humans. Extra carbon dioxide acts like empty calories or “junk food” for the plants, which gorge themselves on it to grow bigger and faster, consequently getting larger but less nutrient-packed. Just like America’s obesity epidemic, which is partially due to people’s increased access to an abundance of calorie-rich but nutrient-poor food, more is not always better.

Agricultural scientists have known for some time that our food has been getting less nutritious, but they thought it was only due to a byproduct of modern farming methods: soil overuse which leads to mineral depletion, or breeders favoring high-yield varieties, which sacrifices nutrition for size. Meanwhile, plant researchers working over the last couple of decades were finding something surprising: that elevated carbon dioxide also contributes to lowering mineral content in plants.

The plant and agricultural scientists each had pieces of the puzzle, but no one put two and two together to fully explain the nutrient depletion phenomenon until recently.

In 1998, a scientist named Irakli Loladze learned that zooplankton starve from nutrient deficiency when eating algae that are given extra light and grow faster. He thought the same thing might be happening with plants as a result of excess carbon dioxide, and his instincts proved right. The phenomenon was dubbed the “great nutrient collapse.”

The implications of this research are troubling for anyone, but especially people in poor or undeveloped areas of the world where it is more difficult to compensate for the lack of nutrients by supplementing diets with more protein and vitamins.

According to the Global Hunger Index, 2 billion people worldwide already suffer from “hidden hunger,” in which people starve consequent to malnutrition even though they are consuming enough calories. Iron deficiency is the top nutritional disorder in the world, one of every three people are affected by inadequate zinc intake, and millions are deficient in calcium, magnesium, or selenium. Diets low in these essential nutrients can lead to impaired cognitive development in children, increased childhood and maternal deaths, reduced growth in infants, and impaired immune function. [more]

Vanishing Nutrients

ABSTRACT: Declines of protein and minerals essential for humans, including iron and zinc, have been reported for crops in response to rising atmospheric carbon dioxide concentration, [CO2]. For the current century, estimates of the potential human health impact of these declines range from 138 million to 1.4 billion, depending on the nutrient. However, changes in plant-based vitamin content in response to [CO2] have not been elucidated. Inclusion of vitamin information would substantially improve estimates of health risks. Among crop species, rice is the primary food source for more than 2 billion people. We used multiyear, multilocation in situ FACE (free-air CO2 enrichment) experiments for 18 genetically diverse rice lines, including Japonica, Indica, and hybrids currently grown throughout Asia. We report for the first time the integrated nutritional impact of those changes (protein, micronutrients, and vitamins) for the 10 countries that consume the most rice as part of their daily caloric supply. Whereas our results confirm the declines in protein, iron, and zinc, we also find consistent declines in vitamins B1, B2, B5, and B9 and, conversely, an increase in vitamin E. A strong correlation between the impacts of elevated [CO2] on vitamin content based on the molecular fraction of nitrogen within the vitamin was observed. Finally, potential health risks associated with anticipated CO2-induced deficits of protein, minerals, and vitamins in rice were correlated to the lowest overall gross domestic product per capita for the highest rice-consuming countries, suggesting potential consequences for a global population of approximately 600 million.

Carbon dioxide (CO2) levels this century will alter the protein, micronutrients, and vitamin content of rice grains with potential health consequences for the poorest rice-dependent countries



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