Why Healthy Humans Need Healthy Soil

You may not be able to see them, but microorganisms in the soil have a big impact on human nutrition and health.


You’ve heard the adage “You are what you eat.” It may even motivate you to buy organic produce free of pesticide residue or seek out foods like grassfed beef or pastured eggs. After all, you are also what your food eats.

But the food chain is more complicated than you may realize.

“If we are what our food eats, we are only as healthy as the soil our food is grown in,” writes integrative neurologist Maya Shetreat-Klein, MD, in The Dirt Cure: Growing Healthy Kids With Food Straight From Soil.

A small but expanding body of research backs this philosophy, demonstrating that the health-promoting properties of our food are inextricably tied to the health of the soil.

After all, soil is not a dead medium. When it’s well managed, it is a vibrant and complex ecology of bacteria, fungi, and other living things — and everything growing in it and eating from it is healthier. Including us.

Where Did the Nutrients Go?

Unfortunately, in modern commercial-farming operations, our soil is too often treated like dirt. Now-common practices like pesticide use and tilling fundamentally change the quality of the soil and what’s being grown in it.

The nutritional value of many of the fruits and vegetables we eat today, for instance, is 5 to 40 percent lower than that of the same produce grown 50 to 70 years ago, according to Donald R. Davis, PhD, FACN, of the Biochemical Institute at the University of Texas in Austin.

In a 2004 study published in the Journal of the American College of Nutrition, Davis reviewed U.S. Department of Agriculture nutritional data from 1950 and 1999 for 43 different vegetables and fruits. He found “apparent, statistically reliable declines” in the amount of protein, calcium, phosphorus, iron, riboflavin, and vitamin C across the group of foods over those 49 years.

Davis built on this research with a 2009 meta-analysis of global studies that noted similar nutritional declines in conventionally grown produce. His conclusion: Modern farming’s reliance on synthetic fertilizers and plant cultivars bred for high yields has led to “trade-offs between yield and nutrient concentrations.”

The good news is that other research suggests that more ecosystem-friendly farming can help plants retain their nutritional bounty.

A 2014 paper published in the British Journal of Nutrition summarized the results of 343 peer-reviewed studies that showed significantly higher levels of phytonutrients in crops raised organically — a conclusion that suggests organic farming supports soil health better than conventional techniques. (For more on how modern farming affects soil health, see “Conventional-Farming Practices That Harm the Soil,” below.)

In another study, scientists at the University of California, Davis, compared levels of flavonoids — phytonutrients that protect against cardiovascular disease, cancer, and dementia — in tomatoes raised organically over 10 years with those raised conventionally during the same time period. They found that the organic tomatoes had much higher levels of two important flavonoids — quercetin and kaempferol — than the conventionally grown tomatoes.

Published in 2007, this study is especially interesting because the organic plots produced similar yields to the conventional fields, debunking the notion that farmers must sacrifice quantity for quality.

Despite mounting evidence linking healthy soil and healthy plants, and showing how industrial agriculture can disrupt and destroy ecosystems, research into the connection between healthy soil and healthy humans is still in its infancy.

“Some of this has to do with the complexities and many unknowns involved in the research,” explains Kristine Nichols, PhD, chief scientist at the Rodale Institute. “Some of it has to do with how new this area of research is, and some is due to a lack of financial support and the costs involved.”

Given that most food and agriculture research is funded by companies hoping to promote their commercial farming products, dollars are not flooding in for research examining whether fewer chemical products and more knowledge of nature would benefit our agriculture and health.

Why Healthy Soil Matters

There are more life forms in one teaspoon of healthy soil than there are humans on the planet, and scientists are still in the exciting early stages of discovering just how these microorganisms interrelate with plants — and with us.

What has emerged from the research so far is evidence of an ongoing barter between plants and the soil’s most miniscule residents. Through the solar-powered energy conversion process of photosynthesis, plants create a sugary carbon fuel that supports their own growth. But they don’t use all this fuel: 40 percent or more is streamed through their roots, delivering energy to microorganisms in the earth. In exchange, these microorganisms feed plants the mineral nutrients they extract from rock, sand, silt, and clay within the soil.

The relationship gets even more complicated. Just as we humans depend upon our microbiome for multiple benefits, plants rely on the soil’s microbiome for chemical defenses against pests, communication with other plants, and more.

Interestingly, in soils with lots of biodiversity, you’ll find some microbes that are closely related to disease organisms, explains Utah State University soil scientist Jennifer Reeve, PhD.

These microbes don’t cause disease, but the plants produce compounds in response to them. In doing so, they develop a robust set of defenses — just in case the microbes’ disease-causing cousins come along. Not only will these plants be able to fight off disease better than those grown in depleted soil, but they can also offer a richer array of phytonutrients to the humans who eat them.

“Plants can’t run away, so they have evolved this huge arsenal of different chemical compounds to protect them against pests, disease, and UV and water stress,” says Reeve. “Many of these chemicals and phytonutrients have been shown to have beneficial activity in human health.”

Soil-Friendly Livestock

Grazing and foraging animals play a role in this dynamic ecology as well. “The meat, eggs, and milk from animals raised on pasture are higher in nutrients than those from animals raised in confinement,” explains Joseph R. Heckman, PhD, a Rutgers University soil scientist.

Heckman tested soils in the mid-Atlantic states and found that those underlying pasture were 60 percent higher in organic matter than those in cropland without animals. “Having those animals on the land is also the best way to build soil quality.”

“Nature never farms without animals,” adds Didi Pershouse, founder of the Center for Sustainable Medicine in Thetford Center, Vt., and author of The Ecology of Care: Medicine, Agriculture, Money, and the Quiet Power of Human and Microbial Communities. “That’s everything from earthworms up to grazing animals.”

Even livestock like cattle can benefit the soil, as long as they’re managed in such a way to prevent heavy grazing that kills plants. They deposit microbe-rich urine and dung, and they cause plants to pulse carbon sugars into the soil ecosystem.

There’s a virtuous cycle when animals are brought onto the land: They make the soil healthier, which makes the plants healthier, which makes the animals themselves healthier — and those health benefits are passed on to humans.

Like soil, animals, and plants, we humans are complex biological systems. As we seek out food that nourishes us, we would do well to consider that our health is deeply connected to the biological systems that produce it. From the ground up.

This originally appeared as “The World Beneath Our Feet” in the April 2017 print issue of Experience Life.

is the author of The Soil Will Save Us.

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