Scientists at Leiden University have found evidence that plants grow faster due to increased CO2. The flip side is that they become higher in calories but less nutritious. The nutritional value of virtually all crops has declined – plants contain less protein, iron, and other nutrients. 

The Leiden study pooled thousands of observations across dozens of crops and nutrients. Its overall conclusion is that elevated CO₂ tends to shift plant composition toward greater carbon and carbohydrate content, while reducing concentrations of several essential minerals and often protein.

Dilution effect

It was already suspected that our food was less nutritious than it had been in the past. Still, the scientists in Leiden have now confirmed this following extensive research: plants grow faster due to increased CO2, but the extra carbon causes them to produce more carbohydrates – and consequently contain more calories. As a result, climate change is making our food less nutritious but higher in energy.

The popular explanation — “the plant grows bigger, so the same minerals are diluted over more biomass” — is partly correct, but incomplete. More CO₂ makes photosynthesis more efficient; plants capture more carbon and produce more sugars, starch, and other carbohydrates. Carbon therefore increases faster than nutrients such as iron, zinc, and nitrogen, creating a dilution effect.

Iron deficiency

The differences are invisible and often not detectable by taste. Still, for people already on the verge of malnutrition and relying on a few staple foods, such as rice or wheat, the drop in nutritional value can make a significant difference.

According to the World Health Organization (WHO), 40% of young children and 37% of pregnant women worldwide suffer from anemia, often caused by iron deficiency. In the worst cases, iron deficiency impairs children’s cognitive development.

Quantity or quality?

For a long time, nutritional value received far too little attention, according to the researchers. The focus was on yield, particularly for rice, corn, and wheat. This remains the case today. However, due to drought and changing precipitation patterns, crops are failing, or agriculture is no longer possible in some areas. If nutritional value also declines, this has consequences for our health. 

It is not just about the quantity of vegetables we eat, either. The quality of the grain also affects the nutritional value of pasta, and less nutritious soy means livestock receive fewer nutrients. That makes a difference to the quality of the meat—and, for that matter, to the quality of meat substitutes containing soy.

More diverse meals

In any case, the scientists believe that simply eating more of the crops currently grown will not solve the problem. “The calorie content is increasing relative to the nutrient content, and most people are already consuming too many calories. Above all, we need to diversify our diets.”

One possible solution could be to ‘breed’ certain crops—using improved seeds or adding nutrients to the soil or directly to the plants via spraying. However, the best solution may well be to reduce CO2 emissions to prevent further deterioration in food quality.

What about food prices?

Nutrient dilution caused by CO₂ does not necessarily make wheat or rice more expensive per kilogram.  Thanks to the traditional CO₂-fertilisation effect, farmers could produce more tons of wheat at the same or even lower cost. But those tons would contain less nutrition. And the price per calorie and the price per nutrient could diverge.

For poorer populations that depend heavily on rice, wheat, or corn, the consequences could be far more serious. People can consume enough calories and still suffer from micronutrient deficiencies. Agriculture could partly offset the decline in nutrient density, but these measures come at a price.

So, to conclude: Climate change could make nutrition more expensive even when farms produce more calories. For Belgium and the Netherlands, more CO₂ could lead to higher yields for some crops, but with fewer nutrients per kilogram.

As a consequence, more breeding, fertilization, and quality control would raise production costs. So, part of tomorrow’s food price could become the price society pays to preserve today’s nutritional quality.