Over and over, I have heard and read claims that the soil growing much of the planet's crops is "depleted" and thus our foods do not have sufficient minerals, vitamins, and other nutrients.

Five examples of such claims:

  1. https://naturalsociety.com/nutrient-depleted-soil-soon-impossible-crop-growth-big-ag/

    We take so much for granted: water, food, clean air, and the earth we walk upon—which, by the way, is changing for the worse under our very feet. Thanks to aggressive farming techniques by factory farms, our soil is becoming depleted of necessary nutrients. Very soon (and sooner than we’d like), it may be difficult to grow much of anything.

  2. https://thehealthmoderator.com/u-s-agricultural-soil-depleted-85-percent-minerals-100-years/

    “The soil lacks the nutrients to keep people healthy and they become susceptible to disease”, said report authors John B. Marler and Jeanne R. Wallin. The problem, according to a study undertaken by head researcher Don Davis, of the University of Texas Austin’s Department of Chemistry and Biochemistry, is that modern agricultures’s focus has been on size, growth rate and pest resistance, not nutritional content of the plants produced. The plants, unable to keep up with growth, cannot manufacture and fully uptake soil nutrients.

  3. https://thebalanceyouneed.com/our-health-and-soil-depletion/

    Perhaps the best summary is by Dr. William A. Albrecht, Chairman of the Department of Soils at the University of Missouri, who said:

    “A declining soil fertility, due to a lack of organic material, major elements, and trace minerals, is responsible for poor crops and in turn for pathological conditions in animals fed deficient foods from such soils, and that mankind is no exception.” This is how soil depletion affects our food and health.

  4. https://www.dailymail.co.uk/health/article-207652/Why-apple-today-good.html

    Fruit and vegetables are being gradually stripped of the natural goodness which makes them beneficial for health, experts have found.

    An alarming drop in essential minerals means that the apples and greens of today are nowhere near as good for us as those eaten 50 years ago.

  5. https://www.theguardian.com/uk/2006/feb/02/foodanddrink

    The research, which is contested by the food and farming industry, found a marked decline in nutritional value during the period.

What is the truth? Is food becoming less nutritious because of depletion of soil minerals and nutrients?

I am skeptical because dozens people I know do not supplement their food with anything, and they do not appear to be having symptoms of any deficiencies. They claim they have no symptoms and that supplementation is unnecessary. Of course, they could have symptoms of which they are not aware (or are not easily visible), or could develop symptoms later in life.

  • 1
    Which claim are you specifically targeting? That crop soil is (becoming depleted)? Or that food is less nutritious because of it?
    – user2276
    May 13, 2019 at 22:36
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    Big problem here: The only things we need that could even come from the soil are minerals. All vitamins and other nutrients are synthesized by the plant (or the animal that ate the plant.) May 14, 2019 at 5:00
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    @LorenPechtel If minerals are depleted from the soil, is it possible that the plant does not synthesize as many vitamins and nutrients? May 14, 2019 at 7:20
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    @LorenPechtel From soil to plant to plate composition to nutritional value to health/deficiencies. This is too broad: "Food", "nutritious", "soil" all this needs to be narrowed down and defined: British bread is now drastically lower in Se, because it's now more from British wheat instead of imported (which still has more Se than British wheat). "Has the mineral content on the same plots of land decreased?" (Which would lead to plants having a harder time accumulating stuff that's no longer there. Was soil and humus eroded?) Currently, character limit for answers prevents a proper answer. May 14, 2019 at 13:19
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    If nutrients are not present for the plant to take in, does that mean I'll have less vitamin C, or would that simply result in the plant being smaller, weaker or fruit not being produced? Does it mean the plant itself forms just fine, but is missing what humans consider nutrients? I don't think there's a direct "nutrient" transfer from soil and air into edible plant product, per se. May 14, 2019 at 17:28

5 Answers 5


Avery gave you a list of "yeses" by moving the goal posts to an issue of organics vs non-organic modern agriculture. Here's a peer-review no to the actual question of historical decline: https://doi.org/10.1016/j.jfca.2016.11.012 It's a study by an employee of Canada's Bureau of Nutritional Sciences

  • 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.

Comparisons of food composition data published decades apart are not reliable. Over time changes in data sources, crop varieties, geographic origin, ripeness, sample size, sampling methods, laboratory analysis and statistical treatment affect reported nutrient levels. Comparisons with matching archived soil samples show soil mineral content has not declined in locations cultivated intensively with various fertilizer treatments. 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.

It's an open access article by the way, which also reviews/criticizes the Thomas etc. studies (which were the main topic of the Guardian and Daily Mail). The Thomas report is from the year 2000, so there must have been some slow news day in 2006 for it to become newsworthy all of a sudden...

As to pick a modern study that has wide historical range (from that review)

Avoiding the potential pitfalls of depending on historical analytical data, Fan et al., 2008a, Fan et al., 2008b conducted laboratory mineral nutrient analyses of wheat grains and soil samples archived over the last 160 years by the Broadbalk Wheat Experiment, established in 1843 at Rothamsted, U.K., and run continuously ever since. They found that the grain concentrations of Zn, Fe, Cu and Mg remained stable between 1845 and mid 1960s but since then significant decreases were seen in Zn (P = 0.004 to <0.001), Cu (P = 0.021 to <0.001) and Mg (P = 0.030 to =0.004), which coincided with the introduction of semi-dwarf, high-yielding cultivars. With regard to the hypothesis that soil nutrient levels are a causative factor, they found that the mineral concentrations in the archived soil samples either increased or remained stable. Reasons for this included inputs of Mg from inorganic fertilizer, Zn and Cu from farm yard manure, and Zn also from atmospheric deposition. The observed decreases in wheat grain mineral content were independent of whether the crop received no fertilizers, inorganic fertilizers or organic manure. Multiple regression analyses showed that the two highly significant factors associated with the downward trend in grain mineral concentration were increasing yield and harvest index (i.e., the weight of the harvested product, such as grain, as a percentage of the total plant weight of the crop, which for wheat was measured as the aboveground biomass due to the difficulty of obtaining the root biomass).

So basically there is a nutrient change, but due to different cultivars being used in the "good old days", not to any soil depletion in the meantime.

  • 1
    Not a binary problem and thus yes or no are too simple.. But quite a few soils are mismanaged, eroded and depleted, commercial artificial fertilisers deficient in what is removed from soils (and yes, that's a lesser problem in well managed organic farming). Ex: in the same issue of your PDF the Mg deficiency). On the other hand, Cu is used in organic farming so much as pesticide that some soils are anthropogenically over-enriched as to be unsuitably polluted with it. Plus regional differences. Some are now way above N+P capacity, so that it gets washed into groundwater. Please expand. May 15, 2019 at 9:02

Q What is the truth?

That would be nice to know, indeed. But the way this problem is formulated it is way too complex to be answered definitively with simple 'yes' or 'no'.

On the one hand, it's a really simple equation of input/output. If the substrate, fertilizer and water are lacking minerals, then the plants will be lacking them as well, as they generally do not manufacture minerals out of the air. But real world application of this seemingly simple truth is quite complicated.

Looking closely, the old problem of declining soil fertility wasn't solved by the fertilizer industry. In some ways it made it worse in the long term. So bad that that now we have Only 60 Years of Farming Left If Soil Degradation Continues.

At just the point when agriculture was running out of unexploited tillable lands, technological breakthroughs in the 1950s and 1960s allowed it to continue increasing production through the use of marginal and depleted lands. This transformation is known as the Green Revolution. The Green Revolution resulted in the industrialization of agriculture. Part of the advance resulted from new hybrid food plants, leading to more productive food crops.[…] Soil erosion and mineral depletion remove about $20 billion worth of plant nutrients from US agricultural soils every year. Dale Allen Pfeiffer: "Eating Fossil Fuels: Oil, Food and the Coming Crisis in Agriculture", 2006.

Many subproblems to the claim as presented can be answered "yes", for example "many soils are being depleted", "nutrient, here: mineral concentrations in produce, composition is changed compared to 100 years ago". But the certainty that whole string of claims present make it too to be precise about the end result of human health.

What exactly is meant with depletion? Also simple soil erosion? Loss of biodiversity and thus "soil health" or old-fashioned fertility? General downward trend or single constituents of soil? How to evaluate plant nutrients that are present in soil but becoming less available for plants? Do these 'depletions' result in plants that are deficient or just less yield as these nutrients are a limiting factor? How does this translate to what people eat? Are the nutrients diluted in fresh or dry weight? Is this the same across the world or with regional differences? The list goes on but I stop here.

From soil to plant to plate composition to nutritional value to health/deficiencies. This is just a bit n the broad side. "Food", "nutritious", "soil" all this needs to be narrowed down and defined. For example British bread is now drastically lower in Selenium compared to 40 years ago. But not because British soils are depleted of Selenium, but because it's now made more from British wheat instead of imported, which still has more Selenium than British wheat. And since this problem was identified, fertilizer compositions were changed so that now soils get enriched with Selenium.

A more meaningful answer might be derived from asking "Has the mineral content on the same plots of land decreased?" Which would lead to plants having a harder time accumulating stuff that's no longer there. Was soil and humus eroded?

This is not a binary problem and thus either "yes" or "no" are too simple. But quite a few soils are mismanaged, eroded and depleted, commercial artificial fertilisers are often deficient in compounds compared to what is removed from soils via harvests and degradation. Yes, that's often and in general a lesser problem in 'well managed' organic farming.

On the other hand, Cu is used in organic farming so much as pesticide that some soils are anthropogenically over-enriched as to be unsuitably polluted with it.

A big problem for answering this properly are the regional differences. Some soils are now way above N+P capacity, so that it gets washed into groundwater. This effects primarily Western Europe wheras Africa and South America tend to have the opposite problem. But this is again too simplified.

The human health angle is even more complicated than that. Vitamins and minerals and trace elemenst, the maro- and micronutirents in human nutrition are – again – in general not a widespread problem for affluent Westerners who eat a well balanced diet. "Well balanced" being the problem here.

Does it matter that potassium in local carrots declined so much that you now have to eat 12 carrots instead of 7 to obtain the same amount as from one half banana? Is a reduction in minerals in harvested wheat a problem if all of that is in those layers that are discarded for making white flour or junk food anyway? Is the reduced mineral content in broccoli a problem when 60 years ago it was boiled for 45 minutes on average while today it's down to 15 minutes after which the minerals leached into the water are discarded?

Then the secondary non-nutrients in plants, or phytochemicals. These cannot be classified across the board as beneficial, as some are also anti-nutrients, or outright poisons. Some go up, some go down, some are good, some are bad. It depends, and we do not know enough.

Even the basic minerals for themselves in plant products are not "more is better". What is the 'right amount' of nitrate, fluoride, selenium in salad, tomatoes, tea or nuts? Most of these can be overdosed with relative ease, so in some soils it would be beneficial if their levels were reduced so that plants do not accumulate them as much as they do.

Some facts that might help elucidate some subproblems:

Human activities impact several processes in soil that could lead to physical (accelerated erosion, deterioration of soil structure, crusting, compaction, hard-setting), chemical (nutrient depletion and imbalance, acidification, salinization) and biological (depletion of soil organic matter, loss of biodiversity) degradation of soil. Soil degradation directly affects food security through reduction in crop yields, decline in their nutritional quality and reduced input use efficiency. Plant availability of mineral nutrients in the soil is the main source of mineral supply to human beings.
Soil Quality and Human Health, p1.

enter image description here
Fig 1.6 Depletion of agricultural land and nutrient depletion (GLASOD) (Drawn from Oldeman et al. 1991)

Nutrient depletion

World    Asia    Africa  South    North and        Australasia  Europe
                         America  Central America
135 (7)  15 (2)  45 (9)  68 (28)  4 (3)            1 (–)        3 (2)

Table 1.4 Global Assessment of Human-induced Soil Degradation (GLASOD) for different regions (million ha). Numbers in parenthesis indicate percent of total degraded area (Adapted from Oldeman et al. 1991)

Global Assessment of Human-induced Soil Degradation (GLASOD) showed that worldwide 15% of the land covering an area of 1964 million ha is affected by human-induced soil degradation out of which 1642 million ha (84%) is affected by water and wind erosion (Table 1.4). Total annual production of dust by deflation of soils and sediments has been estimated to be 61–366 million Mg. The amount of dust arising from the Sahel zone has been reported to be around 270 million Mg per annum, which corresponds to a loss of a layer of 20 mm over the entire area (WMO 2005). Besides leading to loss of organic matter and plant productivity, wind erosion can cause serious health problems by blowing soil particles, pollutant and microbes into the air, aggravating allergies, asthma and opportunistic infection of the lungs (Korenyi-Both et al. 1992; Peters et al. 2001; Prahalad et al. 2001; Griffin and Kellogg 2004). Airborne bacterial and fungal spores and microbial molecules such as endotoxins and fungal mycotoxins can cause allergic reactions and respiratory stress in children (Braun-Fahrlander et al. 2002). Desert dust in Kuwait during the 1990s was reported to cause cellular membrane and DNA damage (Athar et al. 1998).

Chemical soil degradation covers about 239 million ha (12%) and physical soil deterioration, which includes compaction and water logging, occupies around 83 million ha (4%). Soils affected by pollution occupy an area of 22 million ha worldwide. Recent estimates made by Bai et al. (2008) show that 24% of the global land, often in very productive areas, has degraded during the period 1981–2003. Comparison of degrading areas with global land cover revealed that 19% of degrading land is cropland, 24% is broad-leaved forest and 19% needle-based forests. Comparison, of the new analysis with the previous GLASOD estimates show that much of the area estimated by two approaches does not overlap.

Loss of nutrients is the major sub-type of chemical deterioration of the soils followed by salinization. More than two-thirds of area affected by salinization (76 million ha) is located in Asia. Salinization leads to an excessive accumulation of water-soluble salts such as sodium, potassium, calcium, magnesium, chloride, sulphate, carbonate and bicarbonate in the soil and soil solution. The salinization could be caused through natural processes (primary salinization) or human interventions (secondary salinization). Primary salinization is caused due to high salt contents in parent material or groundwater particularly in arid regions. Secondary salinization develops due to inappropriate irrigation practices such as application of salt-rich irrigation water and/or insufficient drainage. Salinization is considered a major threat in the irrigation systems of the Indus, Tigris, and Euphrates River basins, in north eastern Thailand and China, in the Nile delta, in northern Mexico, and in the Andean highlands (Bai et al. 2008). Dryland salinity, which currently affects about 1 million hectare area in southwest Australia, has been linked to serious human health problems. Jardine et al. (2007) identified several potential human health impacts resulting from dryland salinity viz. wind-borne dust and respiratory health including altered ecology of the mosquito-borne disease Ross River virus and mental health consequences of salinity-induced environmental degradation.

Of the 135 million ha influenced by nutrient depletion worldwide, 68 million ha is located in South America followed by Africa (Fig. 1.6). The official report of the Earth Summit (1992) expressed concern over major declines in the mineral values in farm and range soils throughout the world. This concern was based on data showing that during the previous 100 years, average mineral levels in agricultural soils had declined worldwide, by 72% in Europe, 76% in Asia, 74% in Africa, 55% in Australia, and 85% in North America.

Nutrient depletion can be attributed to soil mining because of insufficient and imbalanced fertilizer use, soil erosion, and leaching. Nutrient depletion is predicted to cause serious problems in the mid-altitude hills of Nepal; in poor soil quality areas of north-eastern India and Myanmar, now undergoing transition to permanent agriculture, and in areas in north eastern Thailand. It is also expected to cause major problems in large areas of Africa under transition to short fallow or permanent cropping, in areas of reduced silt deposits in the Nile delta, in the sub-humid Mesoamerican hill sides, and in the semi-arid Andean valleys, north eastern Brazil, and the Caribbean Basin lowlands, where agriculture is undergoing intensification (Bai et al. 2008). Given the lack of alternatives available to smallholders and their limited resources, soil mining tends to be associated with poverty. In contrast, soils in many developed countries have excess nutrients. For example Western Europe has considerable surpluses of nitrogen, phosphorus and potassium (Bach and Frede 1998). These surpluses are the result of excessive mineral fertilizer input as well as due to addition of nutrients through imported food products that enter the nutrient cycle via animal dung or liquid manure. During the years 2008 and 2010, about 35 million Mg of soy and soybean products were imported into the EU. Soybeans are processed into soybean oil and soy flour. Virtually all the soy flour goes into animal feed (Kotschi 2013). In Asia, high nutrient surpluses occur as a consequence of excessive nitrogen and phosphorus fertilization such as in China, South Korea, and Malaysia (Lin et al. 1996; Tan et al. 2005). Globally, soil nutrient deficits for cereal production (wheat, rice, maize and barley) were estimated at an average rate (kg ha 1 year 1) of 18.7 N, 5.1 P, and 38.8 K, covering respectively 59%, 85%, and 90% of harvested area in the year 2000 (Tan et al. 2005).

enter image description here

Rolf Nieder & Dinesh K. Benbi & Franz X. Reichl: "Soil Components and Human Health", Spinger: Dordrecht, 2017. DOI

While 'mineral depletion in soils' is an almost inadequate oversimplification in itself, the more general and global outlook concerning possible health effects from degrading soils, mainly by that kind of mismanagement that is called conventional or industrialised farming, is a reason for concern. Not yet across the board in developed countries and not a reason for everyone to go out of their way to pop some pills because of undiagnosed but only suspected 'deficiencies'.

Soil degradation affects human nutrition and health through its adverse impacts on quantity and quality of food production. Decline in crops’ yields and agronomic production exacerbate food-insecurity that currently affects 854 million people globally, and low concentration of protein and micronutrients (e.g., Zn, Fe, Se, B, I) aggravate malnutrition and hidden hunger that affects 3.7 billion people, especially children. Soil degradation reduces crop yields by increasing susceptibility to drought stress and elemental imbalance. Strategies include: improving water productivity, enhancing soil fertility and micronutrient availability, adopting no-till farming and conservation agriculture and adapting to climate change. There are also new innovations such as using remote sensing of plant nutritional stresses for targeted interventions, applying zeolites and nanoenhanced fertilizers and delivery systems, improving biological nitrogen fixation and mycorrhizal inoculation, conserving and recycling (e.g., waste water) water using drip/sub-drip irrigation etc. Judiciously managed and properly restored, world soils have the capacity to grow adequate and nutritious food for present and future populations.
R. Lal: "Soil degradation as a reason for inadequate human nutrition", Food Sec. (2009) 1:45–57 DOI: 10.1007/s12571-009-0009-z

Regarding the nutritional supply of known important minerals in human food we've already seen a decline in for example magnesium:

enter image description here
John B. Marler & Jeanne R. Wallin: "Human Health, the Nutritional Quality of Harvested Food and Sustainable Farming Systems", Nutrition Security Institute, 2006. (PDF)

The alleged inadequacy of analytical methods for these comparisons might be addressed in David Thomas: "The Mineral Depletion of Foods Available to Us as a Nation (1940–2002) – A Review of the 6th Edition of McCance and Widdowson", Nutrition and Health, 2007, Vol. 19, pp. 21–55.

Although magnesium (Mg) is one of the most important nutrients, involved in many enzyme activities and the structural stabilization of tissues, its importance as a macronutrient ion has been overlooked in recent decades by botanists and agriculturists, who did not regard Mg deficiency (MGD) in plants as a severe health problem. However, recent studies have shown, surprisingly, that Mg contents in historical cereal seeds have markedly declined over time, and two thirds of people surveyed in developed countries received less than their minimum daily Mg requirement. Thus, the mechanisms of response to MGD and ways to increase Mg contents in plants are two urgent practical problems. In this review, we discuss several aspects of MGD in plants, including phenotypic and physiological changes, cell Mg2+ homeostasis control by Mg2 + transporters, MGD signaling, interactions between Mg2 + and other ions, and roles of Mg2 + in plant secondary metabolism. Our aim is to improve understanding of the influence of MGD on plant growth and development and to advance crop breeding for Mg enrichment.
Wanli Guoa et al.: "Magnesium deficiency in plants: An urgent problem", The Crop Journal, Volume 4, Issue 2, April 2016, Pages 83-91. DOI

The lack of overview currently only allows very limited conclusions to be drawn from that

Implies that a balance of the different essential nutrients is necessary for maintaining health. The eight minerals that are usually analysed are Na, K, Ca, Mg, P, Fe, Cu, Zn.
A comparison of the mineral content of 20 fruits and 20 vegetables grown in the 1930s and the 1980s (published in the UK Government’s Composition of Foods tables) shows several marked reductions in mineral content. Shows that there are statistically significant reductions in the levels of Ca, Mg, Cu and Na in vegetables and Mg, Fe, Cu and K in fruit. The only mineral that showed no significant differences over the 50 year period was P. The water content increased significantly and dry matter decreased significantly in fruit. Indicates that a nutritional problem associated with the quality of food has developed over those 50 years. The changes could have been caused by anomalies of measurement or sampling, changes in the food system, changes in the varieties grown or changes in agricultural practice. In conclusion recommends that the causes of the differences in mineral content and their effect on human health be investigated.
Anne-Marie Mayer: "Historical changes in the mineral content of fruits and vegetables", British Food Journal 99/6 [1997] 207–211. (PDF)


The question about soil depletion with time has been covered in other answers.

Currently, in some areas, soil mineral depletion is associated with lower amounts of minerals in plants and with iodine, zinc and selenium deficiency in humans (Annals of Botany, 2010, sow-wu.nl Centre for World Food Studies, 2006).

Except in the areas with known mineral deficiencies in the soil, there is usually no need for healthy people to take dietary supplements (PubMed, 2012).


Health Consequences of Iodine Deficiency (PubMed, 2007)

Iodine deficiency occurs when the soil is poor in iodine, causing a low concentration in food products and insufficient iodine intake in the population. When iodine requirements are not met, the thyroid may no longer be able to synthesize sufficient amounts of thyroid hormone... resulting in...iodine deficiency disease.

Daily consumption of salt fortified with iodine is a proven effective strategy for prevention of Iodine deficiency disease.


Areas with widespred zinc deficiency in soil include South Asia, Sub:Saharan Africa and South America (Institute for Agriculture and Trade Policy, 2012, p.19). There is a considerable overlap between soil zinc deficiency and zinc deficiency in humans (ResearchGate). A major contributor to zinc deficiency is a cereal-based diet, which is high in phytates, which inhibit zinc absorption.

Zinc deficiency can cause growth retardation and diarrhea, among other. Both can be prevented by zinc supplements (Linus Pauling Institute).


Keshan Disease, Selenium Deficiency, and the Selenoproteome (The New England Journal of Medicine, 2014)

Keshan disease is a disease of the heart muscle (cardiomyopathy) caused by selenium deficiency.

Extensive epidemiologic studies showed that low selenium levels in the soil and in local foodstuffs correlated with low selenium levels in whole-blood and hair samples from residents in areas where Keshan disease was endemic, as compared with other areas in China.

In response to these studies, the government implemented nutritional policies promoting oral selenium supplementation, which virtually eliminated Keshan disease in areas where it was endemic.


The massive decline in plant compounds is attested by many studies, but I take it that your concern is whether this is linked to problems in human nutrition. The current answer is that there is not enough research on this subject.

Reeve, J. R., et al. "Organic farming, soil health, and food quality: considering possible links." Advances in Agronomy 137 (2016), 319-367.

Our goal is to summarize the management factors that influence soil health, review the literature on the links between soil and plant health, and then discuss possible links with produce quality and human health, with a focus on nutrition and plant secondary compounds (PSC).


Despite growing evidence that organic management does result in greater concentrations of PSC, several current reviews suggest that evidence of nutrition-related health benefits from the consumption of organic foods is limited (Johansson et al., 2014; Lairon and Huber, 2014), or currently lacking (Dangour et al., 2010; Smith-Spangler et al., 2012), that PSC are not nutrients, and that it is still a matter of debate whether these compounds have any positive effect on health (Dangour et al., 2010; Smith-Spangler et al., 2012).


More attention needs to be given to the effects of growth rate and yield on final plant nutrient concentrations when making comparisons between management. Finally, more research is clearly needed on appropriate statistical methodologies, especially in emerging fields such as metaanalysis.

Nevertheless, from the point of view of the consumer purchasing foods in the marketplace, it may be that the large variations in climate, soil type, cultivar, input intensity, growth rate, and productivity across farms largely swamps out any potential differences in nutrient concentration due to management.

So, to address the Guardian article linked in the question, it is based on a simple (and non-peer reviewed) comparison of nutrients in 1940 meats and cheeses compared to 2002. The Advances in Agronomy article observes that are many other possibilities regarding the origin of this decline, and we have no proof that the decline of secondary compounds is the largest cause.

This is not to say that organic and non-organic fruits and veg are nutritionally equivalent. A review of the Advances in Agronomy article notes that it did not include a study indicating that "consumption of organic foods may, however, reduce exposure to pesticide residues and antibiotic-resistant bacteria." Also, this answer does not address the other reasons to prefer organically farmed food, such as desertification.

  • "The massive decline in plant compounds is attested by many studies," what, wait, which? (plz ref that) It is different for selenium or iodine, and Diesel effects on soil and water are a completely different story. Bacteria, fungi and plants manufacture what we need out of thin air, plain dirt and just water? Soil health, thickness, etc, all debatable esp erosion of specific factors; but: that is mainly viability & productivity, which is not exactly the same as 'nutritional health effects for herbivores'. May 14, 2019 at 0:07
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    @LangLangC the article i linked contains the following citations for that statement: Stinner and Blair, 1990; Karlen et al., 1990; Edmeades, 2003; Stinner, 2007; Carr et al., 2013a; Delate et al., 2015; Reganold et al., 1993, 2001; Mader et al., 2002; Edmeades, 2003; Pimentel et al., 2005; Gomiero et al., 2008. see the link for full refs
    – Avery
    May 14, 2019 at 0:20
  • Your link says; "Despite the widespread consumer belief in the superiority of organic foods, research on the topic continues to be plagued with flaws and inconsistencies", and the refs about 'soil health' translate to stability of harvests. Secondary plant compounds (of uncertain value) do not result from "lack of depletion". "Depletion" means no NPK, no iodine etc. but secondary phytochemicals within the same cultivar are in part the result of plant stress (eustress and distsress in more natural environment), not so much lack of nitrogen in soil (easily corrected). May 14, 2019 at 10:08
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    I believed this question was asking about human nutrition, and answered accordingly. If you believe this question is asking primarily about soil health you can write your own answer
    – Avery
    May 14, 2019 at 12:28

Note: I'm posting this as an answer, even though it does not address the question asked directly, because it is too long to be a comment and I think it makes an important point.

There are a few important flaws in this statement:

[..]dozens people I know do not supplement their food with anything, and they do not appear to be having symptoms of any deficiencies[..]

  1. The dozens of people that you know don't count for much in these circumstances. Seeing any effects requires significant timelines and very large populations. People are also notoriously poor at self-reporting. This applies to both whether or not they are supplementing or having adverse health effects. It's good to be skeptical, but just as we shouldn't accept results based on anecdotal evidence, neither should assume nothing is wrong because we haven't noticed it.

  2. Many countries have legislation requiring that certain foods be fortified with various vitamins and minerals to promote good public health. For example:

    • Vitamins A & D in dairy products (Canada, US, variable in Europe, limited in Australia & New Zealand)1
    • Iodization of table salt (Canada, US, China, India)2
    • Fortification of flour (Canada, Australia, UK, Chile,Argentina (wheat only); US (wheat, maize, rice); Mexico, Brazil, South Africa (wheat and maize))3
    • This list is not exhaustive in any sense. See @Jan's answer regarding zinc and selenium.

    It is to point out that in many countries, many potential nutritional deficiencies are compensated for by eating a 'normal' diet. The diet of individuals is supplemented even if they do not take additional vitamins and minerals (such as a daily multivitamin).

    A quick search suggests that countries without legislation regarding supplementation of foods, particularly vitamins A and D and iodine have populations with higher rates of deficiencies. 4, 5,6

    Again, the point here is that in many countries our diets are already getting supplemented, without any additional action on our part (I live in Canada).

  3. Your question also takes for granted that there would be some health benefit to additional supplementation (for example, taking a daily multivitamin). The scientific consensus is that for the general population there are no overall health benefits for taking multivitamin supplements.7

As I mentioned above, I realize that this does not in fact answer your question. I hope however that it helps add to the overall understanding of the complexity of the situation when it comes to nutrition and health, as well as a reminder about common biases and logical errors.

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