‘What Your Food Ate’: Connections between soil health and human health

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“Soil is as diverse as people,” says biologist Anne Biklé. “It’s a complex picture, but when you set away from the details, the takeaway is — the better the health of the soil, the better the crop is in terms of compound, molecules, and nutrients that our bodies thrive on and need.” Photo courtesy of Shutterstock.

Good food starts with soil. Soil is the blank canvas where all food starts. It's what food consumes, but it's rarely considered in discussions about what we should eat. In the book, “What Your Food Ate: How to Heal Our Land,” David R. Montgomery and Anne Biklé sift through the science of soil and how it affects human health.

KCRW: Talk about the beneficial compounds in food, and whether or not they've changed over the past 100 years.

David R. Montgomery: There's a number of health-beneficial compounds in food, and there's evidence that they've declined over the last century, in terms of mineral micronutrients. And they're important for health in terms of phytochemicals, compounds that plants make in response to environmental stimuli, and for their own health, but then, when consumed by us, have benefits. The mix of fats in meat and dairy have changed over the last century, as the diet of our livestock has shifted. There's evidence for changes for each of those. And we go into in the book, what the scientific background and basis for that is, the evidence for it, and what it may mean for human health.

Is there a straight line between soil health and human health?

David R. Montgomery: It's an interesting series of connections between soil health and human health. Soil health will influence the health of plants and crops that are grown in it. What gets into those crops will influence the health of livestock, and what's in meat and dairy products, and what that gets into, in terms of human health, and what's in our food – literally what our food ate. How it got there can influence human health. It's a complex set of relationships that we try to lay out the science behind. So it's not a simple connection. But you can chart the connection right on through.

Can you give us an idea of the variety of nutrition available to us by eating a plant, depending upon how it has been grown?

Anne Biklé: Soil is as diverse as people and a lot depends on context. But generally, soil that's higher in organic matter has higher biological activity. Most of that biology is oriented toward the plant and how the plant, and all these organisms in the soil, especially the microbes, are communicating with one another. When all is good and normal, and communication is flowing, what is happening is that this whole process suffuses plants with generally higher levels of phytochemicals, vitamins, and particular kinds of micronutrients.

Studies vary on that, anywhere from a doubling to maybe as much as a tripling or quadrupling, again, that would depend on the specific mineral that might be being studied or might depend on the particular phytochemical, whether that's something like beta carotene in a carrot or a squash, or whether that's sulforaphane, which is found in all members of the broccoli family. The actual amount, it's a little bit hard to pin down and say all the time across the board, every carrot grown in healthier soil will have this much more. So it's a complex picture. But when you step away from the details, the takeaway is that the better the health of the soil is, the better the crop is in terms of the kinds of compounds, molecules, and nutrients that our bodies actually thrive on in need.

In order to give us an idea of the difference in soil health, can you share the story of the farmer who treated adjacent wheat fields differently?

David R. Montgomery: One of the first looks into the differences farming practices can make on the micronutrient content of foods came our way when we ran into an example of a farmer who’d done his own experiment on two adjacent fields in Northern Oregon. He was interested in whether or not he could do weed control by using cover crops and methods other than the traditional glyphosate, rich fallow conventional practices. He planted two fields side-by-side with a wheat crop and grew them out for two years – one with conventional practices and the other with regenerative practices that involve no-till and with a diversity of cover crops. 

When we found out that he had done this experiment already, we offered to test some of the samples for a suite of minerals that were in them, including the macronutrients and mineral micronutrients – ones that are important for human health. What we found was that systematically, the ones that were grown in the regenerative practices, the cover crop and diverse field, had higher values of most of the mineral micronutrients that we tested. 

We tested this full suite of minerals in the lab at the University of Washington. The most striking result was that the zinc content – and it's an important micronutrient for human health as there's major zinc deficiencies and many populations around the world – the zinc content was 50% higher in the same variety of wheat grown literally right next door. After two years of soil building regenerative practices, you can't increase the amount of zinc in the soil that fast no matter what you add to it really, unless you had a whole bunch of zinc, which they didn't do. But what you can do is bring the soil life back into play, to get the zinc out of the soil particles and into crops. And that was a real eye-opening moment for us. 

It's anecdotal, but that led us down the path of starting to ask the question more broadly of how generalizable might this be? Could it apply to other things like phytochemicals, and vitamins in crops? It was a very intriguing and interesting example of how important soil biology can be, to what gets into our food, and it opened the whole door to thinking about, what did our food eat? What does a plant eat? How do you treat the land?

David R. Montgomery and Anne Biklé research how the nutrients in soil make it into our diets in their book, “What Your Food Ate: How to Heal Our Land.” Photo courtesy of W.W. Norton & Company.

With conventional farming, is there a way to avoid negative impacts on soil life?

David R. Montgomery: It's an interesting question, because it depends what you mean by conventional farming. One of the things that I did in a previous book was look at how farmers who had been adopting regenerative practices of no-till cover crops and a diversity of rotations were able to improve and enhance their soil – build their soil health – and we did some testing of that for “What Your Food Ate,” and it seemed to pan out pretty well. 

But most of those farmers that we interviewed in the growing revolution were conventional farmers in the sense that they were not organic farmers, some of them still use some agrochemicals. But they used a very different suite of practices that were soil-health building. I think if we adopted a different view of what conventional farming is, one could do it without being fully-organic, in terms of helping to build soil health and fertility. But many organic farmers have practices that already build soil health and fertility. So what we're kind of arguing is to look less through the lens of organic versus conventional, and more through the lens of what builds soil health. And there's a lot that conventional farmers can do to do that short of going organic.

You mentioned no-till in your answer. Let's talk for a minute about the plow, which you call a double-edged sword.

David R. Montgomery: I'm a geologist by training and my entry into thinking about soil and soil health was really through the lens of how land degradation affected past societies. That book is called “Dirt: The Erosion of Civilizations,” and it got me into looking at how tillage actually could degrade the health of the land through degrading soil organic matter, degrading soil life. And that was a real eye-opening book in terms of looking at how those connections actually worked.

Let's talk a little bit about the process in which plants eat?

Anne Biklé: It's an interesting question for a human being to consider. Because we might think, where's the tongue? Where's the stomach? Where's the teeth? But plants are obviously really different from us. 

I'll start with the teeth. They're the first chompers for the digestive system of a plant, and they're breaking down and deconstructing larger pieces of organic matter, like a wood chip, or a piece of animal manure, or something like that. But gradually, as that organic matter moves through their bodies after they've eaten, it gets reduced into smaller and smaller particle sizes, different kinds of compounds, and so on. Then, other members of the soil community feast on those things. Eventually, that also feeds into the very smallest members of the soil community, and this is where plants also contribute things. 

Plants are doing their part through taking their ability to photosynthesize, and they manufacture a slew of different kinds of things that they put together in these cocktails that are called exudates. And just like that word sounds, these exudates, they exude, they flow out of a plant's roots, right near the root. And that's where you have legions of microbes waiting to lap up all of those exudates, because they're really basically meals for microbes. This is fats, and proteins, and carbohydrates, and other kinds of things. The microbial world is feasting on plant exudates, the microbial world is also getting sort of a trickle down effect from some of these larger soil organisms. 

So in effect, the plant's stomach is actually the soil. What all these different forms of soil life are doing is digesting all of this organic matter and putting it into forms that the plant can then take back up into its body, and put to use for all of the things that the plant body needs to do. For example, it would turn a flower into fruit, get bigger, and so on. So it's a pretty different way of thinking about eating. 

We now know that the microbial world is absolutely instrumental to the way that plants consume food and in many ways, regardless of their practices, they're like the dietitians and the nutritionists for our crops. Depending on what you feed your crops, you get crops with different levels of phytochemicals, micronutrients – which are vitamins, and minerals. That's what the plant body is up to when it's eating.

What happens when you grow plants without soil hydroponics?

Anne Biklé: The soil microbiome – especially around the roots of a plant in soil – is a whole different membership than the microbiome in a hydroponic system. I haven't seen a really detailed examination of how those two microbial communities differ, but we know that they do. And we also know that probably these exchanges between plants and its microbiome, they're exchanging different things – the plant is likely pushing out different kinds of exudates. The microbes are providing different kinds of nutrients if they're doing that at all. 

Typically, hydroponic systems rely on synthetic inputs of some sort, because plants can't just grow on water. So that is a good question. Another factor depends on how plants are bred. There may be some plants that do okay in a hydroponic system, while others may have a better nutritional profile when grown in the soil. There are aquatic plants out there, like seaweeds and things like that. But those are plants that evolved to specifically grow in a watery habitat, whether it's freshwater or saltwater. Take a nut tree like a walnut tree – you're never going to be able to grow on that tree hydroponically. That's a whole new world to explore when it comes to agriculture.

Did you have a takeaway about whether or not there's enough good soil to globally grow healthy food for everyone?

Anne Biklé: The situation with soil is interesting. I think David and I both think we're optimistic about it. It's one part of the environment that you can change the outcome for crops, provided you start changing your practices and you start taking soil biology into account – feeding the soil biology, the diet on which it thrives.

Just think about any person who's done a dietary change. You don't see any changes 24 or 48 hours. But you do a radical dietary change, and in a week or two, start noticing changes whether they're digestive changes, or changes in your skin, or your hair. The same can be true for soil. Part of this has to do with this really rapid turnover in microbial life. They're not living for decades, they’re living from minutes, to hours, to days. 

As soon as you start changing the diet for soil microbes, they start producing really different metabolites and start having different conversations and communication with plants. The bottom line: Area's organic matter, whether it's the exudates flowing out of a plant, or whether it's a dead plant and animal parts themselves, and even including animal manure, you change that diet for the soil, you change the diet for the crop. That can happen with farmers that we've talked with. 

You can start turning soil around in as little as a couple of seasons. We actually did that at our home in Seattle. Not that we're growing crops, but we put a garden in and the soil was like dead dirt. It was after several years of adding different and diverse types of organic matter that things really started to respond. It's a good-news story in that you can change the soil, and you can change it pretty rapidly. 

Everything from subsistence farmers, to large-commodity farmers in North America can make the change. As you start treating the soil differently, your crops can start changing too. What we found is that the more you rely on building up your soil health, the less you can rely on artificial inputs, whether those be fertilizers or pesticides, because the soil biology is now up and running again. It can do the things that in fact, it's always done for the botanical world.