Today’s topic is one that I covered over ten years ago—the claim that today’s fruits and vegetables are less nutritious than they were in previous generations, due to nutrient depletion of the soil they are grown in.
Are fruits and vegetables getting less nutritious thanks to soil depletion? Let's take a look at some of the latest research.
Nutrition Diva is hosted by Monica Reinagel. A transcript is available at Simplecast.
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Hello, I’m Monica Reinagel and this is the Nutrition Diva podcast, a show where we take a closer look at nutrition research, trends, and claims to help you make sense of the often conflicting and confusing information that’s out there.
Today’s topic is one that I covered over ten years ago—the claim that today’s fruits and vegetables are less nutritious than they were in previous generations, due to nutrient depletion of the soil they are grown in. I debunked this notion back in 2010 but it is still making the rounds. And since my original episode, there is some newer research to share.
If you’ve been listening to this podcast for any length of time, you probably know that I believe that you’re usually better off getting your nutrition from real food than from dietary supplements. There are some cases where supplements make sense. For the most part, though, if you’re eating a healthy diet, you really shouldn’t need to take handfuls of vitamins as well.
However, those who sell supplements (or profit some other way from promoting the notion that we need them) sometimes suggest that we all need to take supplements just to make up for the fact that fruits and vegetables are less nutritious than they used to be. They argue that modern agriculture has depleted the soil of nutrients and rendered our food supply nutritionally bankrupt.
It is true that growing crops removes nutrients from the soil. And over time, soil that’s farmed intensively and constantly can become depleted of certain nutrients. However, farmers are well aware of this danger.
Nebraska-based farmer Diane Karr, writing in 2019, put it this way:
“We have to be very intentional about caring for the soil or it won’t be productive… Many of our fields have been farmed for decades, even beyond a century, and keeping this soil viable into the future is a necessity. Especially after the disaster of the Dust Bowl that our grandparents and great-grandparents endured almost a century ago, it’s been instilled in us that nurturing the soil is an absolute priority.”
On Karr’s farm, for example, they use practices such as no-till farming, cover crops, grazing livestock, and pay close attention to soil nutrient levels to ensure the ongoing health and productivity of the land.
Of course, some of the minerals that fruits and vegetables absorb from the soil aren’t necessarily required for healthy plant growth—but do contribute to the health of the animals and humans that eat those plants. Over time, these nutrients could be depleted. And if this doesn’t noticeably affect the crops, farmers might not bother to replenish them. As a result, the level of some nutrients in fruits and vegetables could decline. That’s the theory, anyway. So, what’s the evidence?
Back in the 1990s, British researchers compared nutrient data collected on fruits and vegetables in the ‘50s and ‘60s with more recent nutrient analyses. They found that the calcium content of modern vegetables was about one-fifth lower than what was measured in the 1960s and average copper content declined almost 80%.
Some years later, US researchers did a similar analysis and found that amounts for a few nutrients like vitamin C, iron, and riboflavin declined somewhat, several were the same, and a few actually increased.
These studies are widely—but very selectively—cited in books, articles, and websites that sell nutritional supplements. You never see any mention of the fact that the level of some nutrients has apparently increased in the last 50 years, for example.
Instead, the 80% decline in copper levels observed in the British study is frequently translated as, “Fruits and vegetables have lost 80% of their nutritional value,” which is obviously a gross mischaracterization of the findings.
The authors of both studies are very candid that most of the differences are probably explained by factors other than nutrient depletion of the soil—and it’s not at all clear that these changes pose a problem. For example, the dramatic decline in copper levels in vegetables from 1960 to 1990 is probably because copper-based pesticides, which were widely used then, are not as commonly used now.
When you actually read the studies, it becomes clear that a lot of the differences are most likely the result of changes in sampling methods and measurement techniques, geographical variation, and the random variation in nutrient values from one pepper or strawberry to the next—which is much more significant than most people realize.
Since those two studies, several research teams have attempted to address some of these methodological issues. For example, they got a hold of some actual soil samples from the 50s and 60s and were able to do a side-by-side, contemporaneous analysis and comparison with modern soil samples. They found that “Comparisons with matching archived soil samples show soil mineral content has not declined in locations cultivated intensively with various fertilizer treatments.”
To the extent that the nutrient content of our produce has changed, the biggest factor appears to be that we simply grow different varieties than we used to. Humans naturally prefer fruits and vegetables with more sugar and starch and the varieties we’ve cultivated over the millennia reflect those tastes. (I talked more about this in Episode #238, “Have we bred the nutrition out of our food?”)
But some of this is also driven by market forces. Vegetables have been intensively bred to increase yield, decrease time to harvest, and have greater resistance to pests and disease—but not necessarily not to improve nutrient content. Produce that grows more quickly, for example, is harvested sooner and therefore has less time to absorb minerals from the soil.
However, as consumers have become more focused on nutrition, breeders are now concentrating on producing fruits and vegetable varieties that boast higher nutritional value. There’s also been a big resurgence in heirloom varieties, with people returning to strains that may be more similar to those we were growing back in the 1950s and ‘60s or even earlier.
In response to concerns about mineral depletion, many farmers (and regular gardeners) are also taking steps to replenish the soil with mineral-rich amendments like rock dust, in addition to the regular organic fertilizers.
My point is that there are a lot of factors that influence the nutritional value of fruits and vegetables—and I think many of them are actually trending in a positive direction. In the meantime, even if some vegetables are a little lower in certain minerals, I don’t think this is as big a deal as some people think.
In my view, skimping on your veggies poses a far more present danger to your nutritional well-being than nutrient-depleted soil. As long as you’re eating a healthy diet with a nice variety of fresh fruits and vegetables, you should still have your nutritional bases covered.
The average American adult is still eating just one and a half servings of vegetables a day, with only one in ten actually eating the recommended five servings. Fun fact: people who use the Nutrition GPA app that I developed are seven times more likely than the typical adult to eat five servings a day! You can find the free Nutrition GPA app in the Apple and Android app stores.
This is Monica Reinagel, the Nutrition Diva. If you have a question you'd like me to answer, you can email me at nutrition@quickanddirtytips.com You can also leave me a message at 443-961-6206.
If you’re looking for more support for healthy weight management, please check out the tools and resources at weighless.life. where our goal is to help people create habits, mindset, and lifestyle that help them weigh less without dieting. That’s at weighless.life