Are Today's Fruits & Vegetables Less Nutritious Because of Soil Depletion?

It is widely reported that the declining nutritional value of food is due to soil depletion. Is our modern food really significantly less nutritious? Is soil depletion the cause? In this in-depth article, I examine the scientific evidence behind this these claims and explain the concept of soil depletion in detail, including its effect on the nutritional value of plant crops.

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Claim: Our fruits and vegetables are less nutritious today than they were 30 to 50 years ago. Or, you have to eat ten tomatoes today to get the same nutritional value that you’d have gotten from one tomato in the 1950s. Or, modern agriculture is causing soil depletion which makes our fruits and vegetables much less nutritious. Truth: While based on a kernel of truth, these alarmist claims are unsubstantiated by any credible evidence. Let’s look at the source of these claims and then examine why they are undependable.

Introduction
What Is Soil Depletion?
The Myth of Soil Depletion
Source of the Soil Depletion Claims
No Evidence to Support Claim of Soil Depletion
The Dilution Effect
Research Does Not Show That Today’s Food is Not Nutritious Enough to Keep Us Healthy
Summary

When I Googled the phrase “today’s fruits and vegetables are less nutritious” I was shocked to find that the lead result was a Scientific American article, apparently from a column called EarthTalk from Environmental Magazine, from 2011.

This article claimed, in a bold heading: “Because of soil depletion, crops grown decades ago were much richer in vitamins and minerals than the varieties most of us get today.”

This article held that it is true, for instance, that a carrot eaten today has fewer vitamins and minerals than one eaten decades ago.

The main culprit, according to the article, is soil depletion.¹

What Is Soil Depletion?

I would surmise most of you who find this article have already accepted that today’s fruits and vegetables are much less nutritious and that soil depletion is the cause. Soil depletion trends much higher in search than searches around the declining nutrient content of food. To address this then, let’s start with soil depletion.

In natural soil ecosystems, the ‘nutrients’ in the soil are held steady, or near steady, by the recycling of plant materials back into the soil, the addition of animal manure, etc. Little soil erosion or leaching will occur and the overall composition of the soil will remain somewhat stagnant.

In modern agriculture, however, plants remove nutrients from the soil and much less of this is returned to the soil as the plant crops are harvested and brought to market. More nutrients are also lost to soil erosion and dissolved by water drainage (leaching). Farmers seek to put nutrients back into the soil by adding fertilizers and other things.

Older forms of crop production either varied the crop planted on a certain parcel of land, as different plants extract different minerals, or allowed one parcel to lay fallow and replenish naturally while another parcel was being planted.

Modern farming seeks to offset this greater loss by adding straw, cornstalks, stems, roots, manure, ash, phosphate, rock, bone, chemical fertilizers, etc. to the soil. Crop rotation can also play a role. According to the claims presented here, however, modern agriculture has failed to replenish the soils and they are becoming more and more barren, resulting in less nutritious fruits and vegetables.

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The Myth of Soil Depletion

It is much harder to ‘deplete’ a soil of minerals than these claims would have you believe and there is no evidence that today’s soils are depleted in this manner.

The evidence that we do have shows that, indeed, the nutrition in modern fruits and vegetables is not declining by large amounts. What I found in my research was that the top sources are presenting no data that supports the presence of soil depletion and poor data to support the claims of significant declines in nutritional content.

Source of the Soil Depletion Claims

Using the Scientific American article as the basis, I figured these claims, as are usually the case, would come from one, or at most two sources. Annoyingly, the article did not link to the studies it cited or even name them.

The first study mentioned is a ‘landmark’ study by Donald Davis, et al. out of the University of Texas and published in the Journal of the American College of Nutrition in 2004.

This study was nothing more than a survey of the USDA’s nutritional data between 1950 and 1999, focusing on 43 different vegetables. This research, according to the article, found ‘reliable declines’ in protein, calcium, phosphorus, iron, riboflavin (vitamin B2) and vitamin C over the period studied. They then assumed the same would be true of other nutrients, like magnesium, zinc, vitamins B-6 and E, but these nutrients were not studied in the 1950s and so could not be included. ¹,²

Ironically, the researcher’s statement the article chose to quote undermined the point of the article:

Efforts to breed new varieties of crops that provide greater yield, pest resistance and climate adaptability have allowed crops to grow bigger and more rapidly, but their ability to manufacture or uptake nutrients has not kept pace with their rapid growth. ³

Newer cultivars designed to feed more people may contain different ratios of minerals and produce different amounts of nutrients. This does not mean they are devoid of nutrients or would even cause deficiencies when included in a healthy and varied diet. Would they have us starve for a bit more calcium in a carrot?

The very reason why these new varieties are grown is that their yield is so much greater than the older varieties from the 1950s. The Davis research does not support the point, however, at all, that soil depletion is a culprit, which is the premise that the article is seeking to support. It simply states that newer, faster-growing higher-yield varieties are measurably less nutritious than their older counterparts.

It remains to be seen if this should make us run to the drug store to purchase a vitamin/mineral supplement or even if the data is reliable. Here is what the study actually said:

As a group, the 43 foods show apparent, statistically reliable declines (R < 1) for 6 nutrients (protein, Ca, P, Fe, riboflavin and ascorbic acid), but no statistically reliable changes for 7 other nutrients. Declines in the medians range from 6% for protein to 38% for riboflavin. ⁴

They concluded that these changes, which were more mundane than they even seem at first glance, were ‘easily explained by changes in cultivated varieties between 1950 and 1999, in which there may trade-offs between yield and nutrient content. ⁵

In other words, they did not claim that soil depletion was the culprit behind the supposed changes and simply decided that these changes were to be expected in our efforts to feed an ever-growing population.

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But, notice that they used percentage of change? Using relative change instead of absolute change will tend to make such changes look huge when in fact they are actually very small in absolute terms. I’ve mentioned carrots, so let’s stick to them and pick a mineral from the research: calcium.

Let’s say that 100 grams of carrot can be expected, on average, to contain about 33 mg of calcium (this is more or less correct). However, in reality, a 100-gram serving will contain around a minimum of 29 mg, and it is quite possible for one to contain up to 39 mg.

Using relative change, a serving with the average amount of calcium, then, contains over 13% more calcium. And a serving with the maximum contains 34% more! This seems like a huge leap but you can see from the raw numbers that, in reality, the absolute change is not all that significant.

Now, if I say today’s carrots have 34% less calcium than a 1950s carrot, you can see that it’s not all that huge a number, after all. But do you notice something else? The apparent change you happened to find in the numbers could be explained by the natural range of the nutrient in any given group of samples.

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Why am I explaining all this? Because the cited research doesn’t consider the fact that the natural range of nutrient content between one sample of vegetable and another can be so broad that ALL the changes noted in the study can be explained by nothing more than natural variation.

In other words, the research, as given, does not seem to prove what the researchers said it proved. They simply found an expected variation in nutrient data that can be explained by the variations that happen naturally.

But don’t take my word for it. A paper by Robin J. Marles called Mineral Nutrient Composition of Vegetables, Fruits, and Grains: The Context of Reports of Apparent Historical Declines put the kibosh on such research. This paper, published in 2017, found that comparisons of food composition data published decades apart are not reliable. ¹ Here are the key conclusions of the report:

- Mineral nutrient composition of vegetables, fruits and grains is not declining.
- Allegations of decline due to agricultural soil mineral depletion are unfounded.
- Some high-yield varieties show a dilution effect of lower mineral concentrations.
- Changes are within natural variation ranges and are not nutritionally significant.
- Eating the recommended daily servings provides adequate nutrition. ²

When I first started researching this, I wondered, how can you compare nutrient analysis conducted in 1950 to an analysis done today? Have not such methods improved and changed? Can we even rely on nutrient data from 1950 to be reliable? Indeed, we cannot. Everything has changed:

Over time changes in data sources, crop varieties, geographic origin, ripeness, sample size, sampling methods, laboratory analysis and statistical treatment affect reported nutrient levels. ³

Simply isolating geographic origin should help you understand the futility in choosing soil depletion as your cause. If your carrot grown in 1950 came from a different country than the one grown in the 1990s, might the soil be different? Wouldn’t this cause changes in the nutrient content without supporting the soil depletion theory? This is but one variable among many.

Simply looking at the results on nutrient databases decades apart is like comparing apples to watermelons. It makes no sense and does not produce reliable data.

This paper also mentioned these relative changes and apparent declines in mineral concentrations:

Contemporaneous analyses of modern versus old crop varieties grown side-by-side, and archived samples, show lower mineral concentrations in varieties bred for higher yields where increased carbohydrate is not accompanied by proportional increases in minerals – a “dilution effect”. Apparent declines, e.g., the extreme case of copper from −34% to −81%, represent small absolute changes: per 100 g dry weight vegetables have 0.11–1.71 mg (1555% natural range of variation), fruit 01–2.06 mg (20,600% range), and grains 0.1–1.4 mg (1400% range); copper composition is strongly subject to the dilution effect. The benefits of increased yield to supply food for expanding populations outweigh small nutrient dilution effects addressed by eating the recommended daily servings of vegetables, fruits and whole grains. ⁴

As I said before, these small changes in nutrient composition, when viewed as part of a balanced and varied diet, should not send us scampering to the drug store for a vitamin and mineral supplement. Any sacrifice that modern cultivars have made is easily outweighed by the increased yield that is needed to feed our growing population.

Now we can see that the first source used in the Scientific American article, that of Davis, et al. was not only not supportive of the article’s thesis but did not say what the article seemed to suggest and may not be dependable at all.

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The second source cited in the article was “A Kushi Institute analysis of nutrient data from 1975 to 1997 found that average calcium levels in 12 fresh vegetables dropped 27 percent; iron levels 37 percent; vitamin A levels 21 percent, and vitamin C levels 30 percent.” ¹

The Kushi Institute ‘analysis’ is actually an article written by a health writer associated with the organization, one A. Jack, entitled Nutrition Under Siege, published in 1998. This writer compared nutrient data in 1975 to 1997. This was not a study by any means and suffers from the same problems as the first source.

It was, of course, not subject to peer review and I would wonder, again, how in the world it ended up being mentioned in an article published by Scientific American. This article has even less merit as a credible source than the previous one, which was at least published in a scientific journal. The Kushi Institute, by the way, was an organization promoting a macrobiotic lifestyle. It is no longer open.

The third source that was, again, not properly cited but merely mentioned with incomplete information (I have to go on searches for these studies), was a ‘similar study’ of British nutrient data. How many similar studies do you need before you decide a bit of variety may be in order? Rhetorical question.

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This third study mentioned appears to be Historical Changes in the Mineral Content of Fruits and Vegetables by Anne-Marie Mayer, published in the British Food Journal in 1997. This paper used the UK Government’s Chemical Composition of Food tables and followed the same tact as the previous sources. This is actually one of the most oft-cited papers on this subject.

Mayer compared the results for 8 minerals, sodium, calcium, iron, phosphorous, magnesium, iron, copper, and zinc from a 1936 report (published in 1960) and the 1980s (1991). She found significant reductions in nutrient content except for phosphorous. She noted that the modern samples contain more water but did not attempt to correct for water content. She also noted that:

…potential sources of deviation included possible differences in the methods of sampling; methods of analysis (although older methods were characterized as taking longer but no less accurate); mixed sources of data for the 1991 edition; greater use of imported and “out of season” produce; different storage and ripening systems; and changes in varieties bred for higher yield, response to modern methods of agriculture, post-harvest handling qualities and cosmetic appeal. ¹,²

Mayer never stated, nor attempted to prove, that any of her ‘significant’ findings were important to human health. She stated that modern agriculture might be causing this reduced mineral content but then stated that more investigation was needed to find out if this was true.

She did not state, nor try to prove, that soil depletion had anything to do with her findings. Instead, she asked, “Is the apparent decline caused by diminished levels of minerals in the soil, poor availability, the choice of cultivars or other changes in the food system?” ³

She also asked many other questions, including whether the data (she relied on) were reliable and to what extent is the decline of minerals of importance to human health.

Her paper was designed not to reach foregone conclusions but to establish areas for further research. Again, this source failed to substantiate the claims in the Scientific American article. She made no far-reaching conclusions and simply stated that this was an area for further research.

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No Evidence to Support Claim of Soil Depletion

So, far, we’ve come up with zilch. Out of the three sources the Scientific American article named, none of them offers reliable data to support the claims that today’s crops are significantly less nutritious and, even if they are slightly less nutritious, that this should be a cause for alarm or make a difference to human health, especially given the relative abundance of food we enjoy in industrialized nations.

But, now we’ve reached the end of the evidence cited. The article that proudly stated in bold that because of soil depletion, crops grown decades ago were much richer in vitamins and minerals than the varieties most of us get today and whose title started with the words ‘Dirt Poor’ offered no evidence at all to support the claim.

Soil depletion was never claimed to be a definite cause in any of the cited studies (or the Kushi article) and the article writer simply assumes that soil depletion is the cause for the (unreliable) data they uncovered. As scientific articles go, this one gets an F for citing evidence that fails to support its claims.

Of course, I didn’t just choose to pick on one article. This article can be considered representative of all such articles. Because, as we shall see, the foregone conclusion, that today’s soils are depleted and nutrient-poor, is not foregone at all.

Remember I said that the first study’s statements argued against the premise of the article, that soil depletion was the problem?

When Davis, et al. stated that modern higher-yield, faster-growing varieties may be part of a necessary trade-off between food production and (slightly) lower nutrient content, this actually argued against soil depletion. The assumption that modern crops simply grow bigger and faster in depleted soil seems to be a loaded one, does it not?

Most articles stating that today’s crops are less nutritious seem to assume that plants ‘make nutrients’ or absorb nutrients simply for our benefit. As if this process is divorced from the development of the plant itself.

We breed vegetables and fruits to grow bigger and faster and they do this despite what we do to the soil. However, breeding for faster growth and higher yield is only one part of the strategy. Another part is enriching the soil with fertilizers and to use soil testing to ensure the mineral content of the soil.

This is not enough to show that soil depletion does not occur, but it speaks to a need for better research to figure out what’s going on, even if what’s going on may not be as significant as the current hype suggests. Further analysis shows that when changes occur in mineral content over the decades, there is virtually no difference in the balance of minerals between the old and new crops.

This would mean that either all the minerals are being depleted at the same rate, which seems hard to fathom, or that none are being depleted and other variables are responsible for this change in mineral balance. ¹

Even the Davis paper, perhaps the most robust of all the nutrient data studies, found that 28% of the ratios between 1950 and 1999 increased, saying that this would make it difficult to reconcile with an overall mineral-depletion hypothesis. Indeed, they concluded that factors other than soil depletion must be at work. ²

This is not to say that soil depletion does not happen, but that it does not resemble the broad soil depletion of all nutrients as put forth by the popular press and social media accounts. Iodine and selenium are two minerals that tend to be sequestered in plants in relatively large amounts even though neither seems to have any significant role for the plant itself.

You may therefore come upon articles that discuss deficiencies in the selenium content of some soils while iodine has long been a problem, leading to it being added to salt in the United States to stave off deficiencies of this vital nutrient.

Another paper by Davis, containing a review of their own and three other papers, including Mayer, showed even less decline in nutrient content, although the researchers still bent themselves into pretzels to show how significant and ‘unwelcome’ these changes are while still reporting relative change when, once again, this change is within range of natural variation.

Of the 11 out of 33 nutrient comparisons that showed ‘statistically significant’ decreases, the strongest declines were around 17% for calcium and 80% for copper, mentioned before.

As stated, copper shows a high dilution effect (see more below) but it is the very high natural variation that is should be noted. ³ As Marles et al. stated, such nutrient composition studies are only a snapshot of foods available on the market for any given time. ⁴

The Dilution Effect

Some samples of modern vegetables indeed show lower amounts of some nutrients than available nutrient data on older ones. One reason stated for this is the dilution effect. Modern high-yield and larger growing varieties are bread for more carbohydrates. This carbohydrate increase is not accompanied by a proportional increase in micro-nutrient composition.

However, when single crops are studied, research fails to find consistent decreases of certain nutrients. In order to get these significant changes, you have to group a bunch of vegetables, fruits, or grains together into a broad group.

As soon as you look at one crop, the changes become insignificant because of the natural variation of nutrients in the vegetable or fruit, which can be quite broad, especially in the case of nutrients like copper. Some modern varieties even have higher concentrations of certain nutrients.

Regardless, calling something scientifically significant and practically significant are two different things.

Research Does Not Show That Today’s Food is Not Nutritious Enough to Keep Us Healthy

Whether or not a change is statistically significant within the confines of a certain piece of scientific research has nothing to do with whether it is significant in terms of human health. This is very important! All the researchers mentioned here, and other researchers not mentioned, have all stated that despite their finding of statistically significant decreases in the nutrient content of fruits, vegetables, or grains, none of these changes can be claimed to have any significant impact on human health.

I need to point out that I am not attempting to discredit the Davis research or any other research mentioned but only to point out these sources are not adequate, taken alone, to support the hyperbolic claims being made about the lack of nutrition in our modern food supply.

Those making such claims would be a lot better off using the raw data for food nutrient composition to better inform people as to how to make healthy choices in their diet than to comb through nutrient data comparisons so as to alarm people and fool them into thinking that today’s food is not nutritious. And this is what the food alarmist are saying.

They are not saying that today’s fruits and vegetables may sometimes be a bit less nutritious but that they are so much less nutritious that you’d have to eat many many more of them to equal the foods of yesteryear.

Statements such as these are made up. They have absolutely nothing to do with the studies that have been conducted:

You have to eat 10 tomatoes to get the nutrition of one tomato from 1950.
You have to eat 8 oranges to get the vitamin C of one orange from 1970.
Today’s carrots have almost no nutrition compared to carrots from decades ago.

None of this is true. Today’s food is quite nutritious. Might there be trends in soil depletion, breeding, etc. that causes these small changes to become more significant over time?

Yes. Do we have evidence that our food is, at this time, almost devoid of nutrients or so much lower in nutrients that we should all run and scream and seek a return to the good old days of being hunter-gatherers?

No. You can rest assured that the fruits, vegetables, and grains you buy from your supermarket or farmer’s market contain more than enough nutrition to keep you healthy, provided you eat a healthful amount of them, but not an excessive amount. In other words, go forth and eat. You’re good to go.

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According to claims of soil depletion, in modern agriculture, however, plants remove nutrients from the soil and much less of this is returned to the soil as the plant crops are harvested and brought to market while more nutrients are also lost to soil erosion and dissolved by water drainage (leaching).
So, according to these claims, modern agriculture has failed to replenish the soils and they are becoming more and more barren, resulting in less nutritious fruits and vegetables.
It is therefore claimed that today’s fruits and vegetables are significantly less nutritious than in the past due to soil depletion. This claim is not supported by credible evidence and modern soil depletion is a myth.
Reports of small declines in certain nutrient amounts are within the natural variation range of fruits and vegetables and not nutritionally significant.
The studies cited as evidence of soil depletion do not show that soil depletion is the cause of any nutrient decline, nor do they claim this to be true.
Factors like changes in crop varieties, farming methods, and data collection over time likely explain any observed changes in nutrition.
The research does not indicate that today’s fruits, vegetables, and grains are significantly less nutritious. Today’s crops are more than nutritious enough to keep people healthy, as long as a varied balanced diet is consumed.
The increased food supply and yield from modern agriculture outweigh any small nutrient declines.