It’s a hazard of climate change you probably haven’t heard of
by Elena Suglia on December 10, 2018
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.
In countries in which the majority of people rely on a few staple crops and do not eat diverse foods rich in minerals, nutrient collapse may pose serious threats to nutrition. For example, rice and wheat provide two out of every five calories that people consume. Rice alone provides 70 percent of calorie intake in Bangladesh, the world’s eighth most populous country, where malnutrition is already an issue.
One study mapped the geographic distribution of those most susceptible to the impacts of anemia and found that the most vulnerable countries were often the poorest and therefore least able to “buy” their way out of the problem by eating more iron-rich fruit, vegetables and meat.
The immediate threat nutrient collapse poses to human health is clear, but other effects are less studied or unknown. For example, it’s not only humans whose food is becoming less nutritious. One study showed that because of increasing carbon dioxide levels, the pollen that bees eat as an important source of food late in the summer now contains less protein than it once did. Another found that plants produced less nectar when exposed to more carbon dioxide, which can affect pollinators like butterflies and hummingbirds. Scientists know even less about what will happen to herbivores or how that will affect animals higher up the food chain. Will farmed meat from animals like cows and pigs contain fewer nutrients because those animals are eating less nutritious plants? Right now, researchers can only guess.
Interestingly, plants like maize and sugarcane, which use a less common method of photosynthesis, are somewhat less prone to nutrient declines. However, these so-called “C4 plants” make up only about
3 percent of all plant species, and therefore simply relying on more C4 crops for food probably won’t solve nutrient depletion.
In a final irony, one researcher says nutrient collapse may contribute to the rise in obesity because people are eating more starchy plant-based foods and consuming higher quantities of food to make up for their lower nutrition levels. Similar to how the zooplankton starved while stuffing themselves with “junk food” algae that were given too much light, we may all be headed for a bizarre world in which we are surrounded by food that we can’t get enough of while, in reality, we’re starving while simultaneously becoming obese.
Can we mitigate the effects of nutrient collapse? Perhaps, but it won’t be easy. The world’s population is growing, increasing global food demands. Even if we dramatically decreased carbon dioxide emissions starting now, atmospheric levels would still be expected to reach 550 parts per million in the next 50 years or so. Scientists have successfully genetically engineered crops with boosted nutrients. Golden rice, for example, provides people with more vitamin A than other varieties, but this process is lengthy, expensive and unlikely to compensate for the plethora of nutrients and vitamins declining as a result of rising atmospheric carbon dioxide.
In the meantime, scientists are working to improve our understanding of how nutrient collapse will affect animals and humans worldwide. With their efforts, we can better rise to the challenge of keeping the world fed and healthy under this newly discovered, invisible threat of human-caused environmental change.
Elena Suglia is a PhD student at the University of California, Davis, who studies plant responses to climate change on mountains. She is interested in using genomics and modeling to inform native plant conservation efforts, communicating science to the public, and promoting equity and inclusion in STEM fields. She can often be found gardening or reading, and the best book she read this year was She Has Her Mother’s Laugh, by Carl Zimmer.