The reason, oddly, may have to do with climate change.

Rice is a common ingredients in many people's diets. It makes a delicious grain bowl, an important ingredient in sushi, and a go-to base for a nice creamy curry. It's a staple for billions of people around the world. But there's evidence this starchy grain may start losing some of the nutrients that make it so healthy.

New research published in Science Advances found that the expected rise in carbon dioxide levels over the next century, in addition to raising global temperatures, may reduce the protein, micronutrients, and vitamin content of rice.  

"When you look at a country like Bangladesh, three out of every four calories comes from rice," said Kristie Ebi, author of the study, to NPR. "Obviously, that means any decline in nutritional value is very significant."

To test their hypothesis, scientists grew several varieties of rice in experimental fields in Japan and China. They then tested a control rice area and exposed one area to 580 parts per million of carbon dioxide. This is the expected carbon dioxide concentration in the next 50 years if there are no changes to emissions or deforestation, NPR reports.

Changes in nutrients varied based on the variety of rice. The patch exposed to excess carbon dioxide lost between 5-20 percent iron, zinc, and protein and up to 30 percent vitamin B1 and vitamin B5. In addition, folate (vitamin B9), which is essential to the development of brain, spine, and spinal cord in a fetus, declined between 10 to 45 percent, according to NPR.

Some argue that higher levels of carbon dioxide actually increase plant size and production, but researchers found while the yield increased, the nutrient amount did not increase with the size. Researchers found that some varieties of rice are more resistant to environmental changes than others, so scientists now have an opportunity to breed more resistant crops for the future.