Food crops have become measurably less nutritious over the past 50-70 years, with studies documenting declines of 5-40% in key minerals across common vegetables and grains. While many assume this is simply due to depleted soil, the reality is far more complex—and understanding the true causes is essential to reversing the trend.

The Soil Depletion Myth (It's Complicated)

Intensive farming and poor soil management have indeed led to nutrient loss in agricultural soils worldwide. Essential elements like nitrogen, phosphorus, potassium, zinc, iron, copper, and selenium are being removed faster than they're replenished in many regions, compromising both soil fertility and crop productivity.

Soil degradation through erosion, acidification, and declining organic matter further reduces the soil's capacity to supply minerals to plants. Even where fertilisers are applied, the heavy emphasis on NPK (nitrogen-phosphorus-potassium) formulations often overlooks critical trace elements. This creates soils that appear productive but are biologically impoverished and lacking in essential micronutrients.

Here's the surprising part: Long-term analyses of archived field soils reveal that mineral levels haven't uniformly declined, even as the mineral content of crops grown in those same soils has dropped significantly. This tells us that soil quality alone cannot explain the nutrient loss in our food. Instead, modern crop genetics and breeding priorities have fundamentally altered how plants absorb and distribute nutrients.

What's Really Happening: The Dilution Effect

When crops are grown in nutrient-poor or biologically degraded soils, they naturally contain lower concentrations of essential minerals like zinc, iron, and magnesium. Reduced soil microbial activity and diminished organic matter limit nutrient availability. But this is only part of the story.

Historical analyses of wheat, vegetables, and fruit samples reveal substantial declines in mineral and protein content over the past century. Wheat grain, for instance, shows decreases of 30-40% in zinc and iron content despite stable or even improved soil conditions. Comparative studies spanning decades have documented losses of up to 76% in copper and 59% in zinc in various foods.

These dramatic declines point to the "dilution effect." Modern high-yield crop varieties produce more biomass—more carbohydrates, water, and fibre—faster than they can absorb minerals and synthesise proteins. The result is like diluting juice with water: the total volume increases, but the nutrient concentration per serving decreases. You get more food, but each bite contains fewer essential nutrients.

This effect is compounded by elevated atmospheric CO₂ levels, which have risen from approximately 280 ppm in pre-industrial times to over 420 ppm today. Research shows that higher CO₂ further reduces the mineral content of staple crops including wheat, rice, and soybeans.

The Human Cost: Hidden Hunger

The decline in nutrient density has serious implications for global health. Micronutrient deficiencies now affect approximately 2 billion people worldwide, contributing to what nutritionists call "hidden hunger"—caloric sufficiency paired with micronutrient deficiency.

Zinc, iron, and selenium deficiencies are major contributors to anaemia (affecting roughly 1.6 billion people globally), weakened immunity, and impaired growth and cognitive development in children. In developing regions where diets depend heavily on staple crops, reductions in crop mineral content translate directly into widespread nutritional deficiencies. Even in industrialised countries, declining nutrient concentrations in fruits and vegetables may compromise overall dietary quality and long-term health.

The Real Culprits: A Perfect Storm

While soil depletion plays a role, research indicates that other factors are more influential in driving nutrient declines:

High-yield cultivars – Breeding for maximum yield has inadvertently created varieties that produce abundant carbohydrates but dilute minerals and proteins.

Plant breeding priorities – Selection has systematically favoured appearance, shelf life, pest resistance, and yield over nutritional quality.

Unbalanced fertilisation – Heavy NPK use without adequate attention to micronutrients creates nutritional imbalances in both soil and crops.

Soil degradation – Erosion, compaction, and loss of organic matter reduce the bioavailability of minerals that are present in the soil.

Elevated CO₂ and climate change – Rising atmospheric CO₂ directly reduces mineral uptake efficiency in many crops.

Farming system design – Conventional high-input monoculture systems diminish soil biodiversity and microbial networks, while organic and regenerative practices tend to enhance nutrient cycling and uptake.

Together, these factors have created an agricultural system optimised for quantity over quality—plants that grow rapidly and abundantly but accumulate fewer nutrients per unit of food produced.

Can We Reverse This Trend?

The good news is that targeted interventions can restore nutritional value to our food supply. Several approaches show real promise:

Balanced fertilisation and precision nutrient management can optimise the availability of both macro- and micronutrients. Rather than focusing solely on NPK, farmers can apply trace elements where deficiencies are identified.

Biofortification involves breeding or engineering crops to naturally contain higher levels of zinc, iron, selenium, and other essential nutrients. Multiple biofortified varieties have been successfully deployed without sacrificing yield, including iron-rich beans and zinc-enhanced wheat.

Regenerative and organic agricultural practices—including composting, cover cropping, reduced tillage, and diverse crop rotations—rebuild soil structure and microbial communities. These living soils enhance nutrient cycling and improve plants' access to minerals.

Targeted supplementation programmes have demonstrated rapid success. Finland's nationwide selenium fertilisation programme, implemented in the 1980s, successfully increased selenium levels in foods and improved population selenium status within a decade, virtually eliminating deficiency-related health issues.

Whilst no single approach provides a complete solution, these strategies demonstrate that the long-term trend of declining food nutrition is reversible. Biofortification requires sustained breeding efforts and farmer adoption. Regenerative agriculture rebuilds soil health gradually, often taking 5-10 years to show substantial improvements. But the evidence is clear: when we prioritise nutritional quality alongside yield, we can produce both abundant and nourishing food.

The Bottom Line

Mineral depletion in soils does influence crop nutritional quality, but it's not the primary driver of declining nutrient density in our food supply. The more significant factors are high-yield crop breeding, unbalanced fertilisation practices, and environmental changes including rising CO₂ levels.

Addressing this challenge requires a systems approach: breeding for nutritional quality alongside productivity, adopting soil-health practices that support nutrient cycling, and implementing balanced fertilisation programmes that include essential micronutrients. The success of targeted interventions like Finland's selenium programme proves that science-based strategies can reverse these trends within a single generation.

Our food can be both abundant and nutritious—but only if we make nutrition an explicit priority in how we breed crops, manage soils, and design agricultural systems.

References

• Alfthan, G. et al. (2015) ‘Effects of nationwide addition of selenium to fertilizers on foods, and animal and human health in Finland: From deficiency to optimal selenium status of the population’, Journal of Trace Elements in Medicine and Biology: Organ of the Society for Minerals and Trace Elements (GMS), 31, pp. 142–147. Available at: https://doi.org/10.1016/j.jtemb.2014.04.009.

• Bhardwaj, R.L. et al. (2024) ‘An Alarming Decline in the Nutritional Quality of Foods: The Biggest Challenge for Future Generations’ Health’, Foods, 13(6), p. 877. Available at: https://doi.org/10.3390/foods13060877.

• Davis, D.R. (2009) ‘Declining Fruit and Vegetable Nutrient Composition: What Is the Evidence?’, HortScience, 44(1), pp. 15–19. Available at: https://doi.org/10.21273/HORTSCI.44.1.15.

• Davis, D.R., Epp, M.D. and Riordan, H.D. (2004) ‘Changes in USDA food composition data for 43 garden crops, 1950 to 1999’, Journal of the American College of Nutrition, 23(6), pp. 669–682. Available at: https://doi.org/10.1080/07315724.2004.10719409.

• Fan, M.-S. et al. (2008) ‘Evidence of decreasing mineral density in wheat grain over the last 160 years’, Journal of Trace Elements in Medicine and Biology, 22(4), pp. 315–324. Available at: https://doi.org/10.1016/j.jtemb.2008.07.002.

• Krasilnikov, P.V. et al. (2021) ‘Soil Micronutrients, Food Systems, and Human Health at Regional Scale’, Moscow University Soil Science Bulletin, 76(5), pp. 239–255. Available at: https://doi.org/10.3103/S0147687421050033.

• Loladze, I. (2014) ‘Hidden shift of the ionome of plants exposed to elevated CO₂ depletes minerals at the base of human nutrition’, eLife, 3, p. e02245. Available at: https://doi.org/10.7554/eLife.02245.

• Mayer, A.-M.B., Trenchard, L. and Rayns, F. (2022) ‘Historical changes in the mineral content of fruit and vegetables in the UK from 1940 to 2019: a concern for human nutrition and agriculture’, International Journal of Food Sciences and Nutrition, 73(3), pp. 315–326. Available at: https://doi.org/10.1080/09637486.2021.1981831.

• Knez, M. and Graham, R.D. (2012) ‘The impact of micronutrient deficiencies in agricultural soils and crops on the nutritional health of humans’, in Selinus, O. (ed.) Essentials of Medical Geology. Dordrecht: Springer, pp. 517–533. Available at: https://doi.org/10.1007/978-94-007-4375-5_22.

• White, P.J. and Broadley, M.R. (2009) ‘Biofortification of crops with seven mineral elements often lacking in human diets – iron, zinc, copper, calcium, magnesium, selenium and iodine’, New Phytologist, 182(1), pp. 49–84. Available at: https://doi.org/10.1111/j.1469-8137.2008.02738.x.