Is our food becoming less nutritious? Many people claim that the nutrient content in our food has been decreasing over the decades. But is this really true, and should we be worried?

A study published in 2004 looked at 43 different common garden crops. It examines how their nutritional value had changed between 1950 and 1999. What they found was that on average, the protein content of those plants decreased by about 6%, Vitamin C decreased 15%, and vitamin B2 by a whopping 38 percent. They also noticed declines in minerals like iron and calcium. Now, there is some debate around the numbers because. How well could we really have measured those nutrients back in 1950? But there is still concern that the food we’re eating today might be less nutritious than the same vegetables 50 years ago. Several other recent studies also suggest a pattern is emerging.

So if we’re witnessing a nutrient collapse, what’s causing it?

One factor that many people point to is depletion of the soils. Given plants to draw their nutrients up from the soil, intense farming practices were thought to be the cause of nutrient depletion. If you look at micronutrients, there are decreasing levels in plants. But, farmers have always (besides the Dust Bowl of the 1930s) put a lot of effort into maintaining their soils. They used fertilizers to ensure that the plants have all the nutrients they need. This makes makes the soil depletion argument less convincing. We’re still getting big plants. They wouldn’t grow that well if they didn’t have the nutrients they need in the soil.

So why else might nutrients be declining?

Another possibility is that it’s selective breeding. If you look at crops like corn today, they’re barely recognizable when you compare them to the wild corn from which these were bred. Since the advent of agriculture, we have been breeding our food crops. The result has been higher yields, resistance to pests, and adaptation to changes in the climate. We’ve been successful. Crops are now bigger and grow faster than ever before. But are they more nutritious and how does this alter their chemistry? Maybe we’ve accidentally been breeding the nutrition out of our foods in pursuit of other objectives. It’s tough to really assess how big of a factor selective breeding is. We can’t easily compare this produce to the same produce a hundred years ago or a thousand years ago.

So we need something else to be able to determine whether it’s selective breeding causing this decrease or something else. What would be really helpful would be a plant that has never been selectively bred. Where would you find one like that?

Well, this is where weeds come in handy. In North America, there is a wild flower called goldenrod. It’s an important source of protein for bees, but not humans. So it has remained wild and untouched by selective breeding, but how would you know what goldenrod was like 100 or 200 years ago?

Fortunately, the Smithsonian Institute has been keeping hundreds of samples of goldenrod dating all the way back to 1842. Using these samples and samples they collected in 2014, scientists were able to compare modern goldenrod with goldenrod from over a hundred years ago. The results were astounding. They found that there was a 30% decrease in the amount of protein in the goldenrod pollen over that period.

If it’s not selective breeding, what else has contributed to goldenrod becoming less nutritious over the last 150 years or so?

One rather surprising idea was that carbon dioxide could play a vital role. CO2 basically increases the growth of all plants. Over the last couple of centuries, the level of CO2 in the atmosphere has increased a lot. It has gone from about 280 parts per million to over 400 parts per million today. Now, that might not sound like a lot, but if you’re thinking of it as plant food, we’re talking about an increase by almost 50%, and we can see the impact from space. It’s called the greening of the planet.

Scientists have been tracking the impact of CO2 on plants via experiments called FACE, which stands for Free Air Carbon dioxide Enrichment. Their experiments run by injecting more CO2 into the area where plant crops are grown, and they find that wheat, barley, rice and potatoes; they will grow faster if there’s more CO2 in the atmosphere.

But here’s the thing. They don’t necessarily become more nutritious, they simply put on more carbs. In other studies conducted in Japan and China, scientists pumped carbon dioxide into rice crops to simulate the kind of CO2 concentrations expected in 50 years time. On average, protein levels fell by 10 percent, iron by 8 percent, and zinc by 5 percent. But even if you started balancing chemical equations, a lower concentration of nutrients doesn’t necessarily correlate with a decline in the plant’s nutrient contents. It’s called the dilution effect.

So what does all this mean for us?

By 2050 scientists estimate that up to a hundred and fifty million people in the developing world may be on the verge of protein deficiency, due to the decreasing levels of protein in their staple foods. So does that mean we should all be taking vitamins and supplements? Well, no. At least, not yet.

The nutrient declines are small enough that you should still be able to get everything you need from a well balanced diet, Including plenty of fruits and veggies. But, the increasing levels of CO2 and the dilution effect may be exacerbating the obesity epidemic. The thinking goes like this: We feel full, or satiated, when we’ve consumed a certain amount of protein. So if the protein levels are going down We may have to eat more food, more carbohydrates, and more fats to achieve the same level of protein. And that may make us fatter. While this is still a contentious theory, what is becoming increasingly clear is that the changing atmosphere, specifically the rising level of CO2, is changing the food we eat.

Content courtesy of Veritasium