Data dispatch #4: the falling nutritional value of crops

The mineral content of wheat and rice is lower today than sixty years ago. Why is that and what does it mean for how we eat?

Eat your vegetables!

When you were little, your parents probably went to great lengths to see you munch on your greens. And even now, as adults, many of us are inundated with public health messaging around the importance of a healthy diet.

What you might not know is that those vegetables were more nutritious when you were growing up than they are today. Ironically, this means that you need to eat even more of them to obtain the same amounts of essential minerals.

A parent feeding their toddler vegetables. If this photo looks weird, that’s because it’s AI-generated.

In dietary advice, fruits, vegetables, and grains are considered particularly important because they contain a bunch of minerals and vitamins you need for your body to function, such as iron and vitamin A. This led the U.S. Dietary Guidelines for Americans, 2020-2025 to recommend that you get 85% of your daily calories from vegetables, fruits, grains, dairy, and protein—in that order.

But the nutritional value of these ingredients seems to be shrinking over time. An important data point comes from this a recent article in the International Journal of Food Sciences and Nutrition, written by a team of researchers from Coventry in the United Kingdom. They compared data on the contents of fruits and vegetables measured in three different historical periods: 1925-1939 (published in 1940), 1982-1990 (1991), and 2011-2015 (2019). When comparing the same quantities of the same foods over time, they found that the amount of sodium (Na), iron (Fe), copper (Cu), and magnesium (Mg) found in them had significantly declined between the first and the last time point. In some cases, a serving of vegetables got you 50% less of these minerals in 2019 than it would have in the 1930s. [Side bar: I had no idea that you needed to consume copper in your food, but apparently you do. It’s found in meats, nuts, and chocolate, among others.]

Source

Why did nutritional value drop? It’s counterintuitive, but it has to do with the fact that agriculture has become much more successful since the 1960s.

The first reason for this is a revolution that swept the world but remains unknown to most people today. I’m not talking about any military revolution, but about a scientific one: the so-called Green Revolution in farming. During this period (roughly 1950-1970) scientists like Norman Borlaug cross-bred crops to produce new, high-yielding dwarf varieties of staples like wheat and rice. These dwarf plants had smaller, thicker stems, which enabled them to send more energy to their fruits and carry more weight even in bad weather.

Another reason—which surprised me—is climate change. As you may remember from school, plants take carbon dioxide (CO₂) out of the air and, with help from sunlight and water, turn it into carbohydrate molecules (photosynthesis). These carbohydrates make up the bulk of plant tissue. It turns out that today’s higher concentrations of CO₂ in the atmosphere, as well as rising temperatures, allow plants to ramp up photosynthesis and thereby grow faster. Many crops today simply have an easier time growing big than they would have had in the 1960s, thanks to more favorable environmental conditions.

Hybrid crops and climate change, together with innovations in fertilizer and agricultural machinery, led to much larger agricultural yield (weight of harvest per hectare of land) in the second half of the 20th century. This saved the booming world population from starvation, and Green Revolution hero Borlaug rightfully got the 1970 Nobel Peace Prize for his work. The growth in yield was quite dramatic, as you can see on this graph from a 2020 paper:

Trends in wheat yield (tons per hectare) and thousand kernel weight (TKW) of a long-running wheat experiment in the UK. The dashed line represents the introduction of dwarf varieties of wheat in 1968. Source

However, a side-effect was that these bigger crops had a lower relative mineral content. The problem is that while dwarf varieties and increased CO₂ levels allowed wheat and rice to grow larger, the amount of nutrients they sucked up out of the soil stayed roughly the same. In other words, the balance between CO₂ and essential nutrients shifted toward CO₂, which caused crops to contain relatively more carbohydrates and relatively fewer minerals, proteins, and other good stuff. For billions of people worldwide, this change is already leading to “micronutrient malnutrition”: a shortage of vitamins and minerals needed for growth and development.

As one example, the World Health Organization estimates that 42% of children under 5 years of age and 40% of pregnant women worldwide suffer from anemia due to a lack of iron, folate and/or vitamins B12 and A. A primary cause of this problem (although there are others) is the lack of these minerals in people’s diet. Remember that iron (Fe) was one of the minerals whose presence in fruits and vegetables was found to drop by 50% between 1940 and 2019 in the first study I mentioned.

Whether this affects you depends largely on where you live. For low-income countries in South Asia and Sub-Saharan Africa, micronutrient malnutrition is a huge problem—and this demands a global solution.

Estimated cases of anemia in children per region of the world. Source

If you live in a wealthy country with a reliable food supply, it all depends on the choices you make. One interesting nugget I found in my research for this post is the idea that daily energy intake from food may actually have dropped because our lifestyles have changed.¹ Turns out sitting in an office chair makes you less hungry than working in a factory all day! And since eating less food reduces your total mineral intake even more, this can cause problems if you don’t change how you balance your foods.

The solution, then, is to actually follow advice like the 85% rule from the Dietary Guidelines for Americans. As science writer Bárbara Pinho points out in her excellent piece on the topic:

In the UK, vegetables make up a meagre 6.3% of the average shopping basket. Keeping an eye on how the nutritional content of food changes in a changing planet is important, but returning to typical dietary guidelines still seems to be a priority.

In other words, as long as you eat your recommended amount of fruits and vegetables, you will get all the nutrients you need. But as the CO₂ levels in the Earth’s atmosphere keep rising, we might end up having to eat even more greens and grains to obtain the same amount of minerals.

And that, I’m afraid, presents an even bigger dinner-time challenge for young parents. Good luck!

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1. I also found data showing the opposite effect, so I don’t know what the right answer is about this specific point.