How Soil Health Affects Human Health: An Interview with Dr. Daphne Miller

Daphne Miller is an author and a practicing physician who spent time on seven innovative farms around the country to explore the connections among soil, how food is grown and personal health. Dr. Miller is a Clinical Professor at the University of California San Francisco, and a Research Scientist at the University of California Berkeley School of Public Health. Her most recent book is  Farmacology: Health from the Ground Up. Bioneers Restorative Food Systems Director Arty Mangan interviewed Dr. Miller at a past Bioneers Conference.   

ARTY: What was it that made you realize that conventional medicine doesn’t have all the answers for health?

DAPHNE: I was working in Salinas, CA as a medical intern and realized that most of my patients had been harmed by the environment and by the agricultural systems that surrounded the hospital, either from toxins in the soil or in the air, or from labor conditions that were unjust, or from eating foods that were too high in calories and didn’t have enough nutrients. I realized that although I had been in medical school for four years and done all this training, that I didn’t have the tools to help address those issues of the environment, the food system, diet and unjust working conditions.

ARTY: What turned your attention to soil?

DAPHNE: I realized that if I was going to trace all of the disease that I was treating to one thing, it was soil and mistreatment of soil. It was either planting the wrong things in the soil or spraying the wrong things on the soil or using the wrong mechanized practices for treating the soil or having policies that were affecting both farm workers and even the local economy in an adverse way. Everything, in a way, traced back to soil.

ARTY: You actually worked on some farms. 

DAPHNE: I started to realize that our food system was broken. It was not a system that was nurturing us or protecting us, but rather was a system that was making us sick and harming us. I started to look to the medical literature to understand what the models were for growing food and for distributing and processing food that could actually be healthy. I remember the day I went to PubMed, which is one of the premier medical research search engines, and I put in the words “soil health” and “human health” to see what studies would come up. I was hoping that I’d find preventive medicine studies on agriculture and health. Pages and pages of studies came up, but they were all about toxins, lead, heavy metals, tetanus, sewer sludge, etc. Reading these studies, it seemed like soil was a horrible dangerous place. Certainly not a place that you would want to eat from, or let your child play in or stick their hands in or a place where you would spend your profession digging in soil. There had to be another model, a model that actually created healthy soil and healthy farms to protect us, and yet there was absolutely no research on the health-promoting impact of agriculture. 

Dr. Daphne Miller

That’s when I decided to go out and learn from farmers who were farming in a regenerative or sustainable way so I could start to understand from the farm perspective what these models looked like and begin to ask questions that span between the soil and agriculture and ourselves. I wanted to research how farming in a healthy way influences personal health.

ARTY: What did you learn on those farms that informed your medical practice?

DAPHNE: I would say it gave me more of a systems approach or a holistic approach to treating patients because good farmers are not reductionist in the way they think. They think about using many different tools and different natural systems together to farm in the best way possible to protect the soil and protect the microbes in the soil and generate healthy food. I started to borrow from that model in terms of thinking of treating my patients. What are the ways we can actually use the natural system to promote health? 

A lot of the work I do is not in the clinic; it is as a healthy farming advocate working on issues around policy, pushing research, and thinking about how hospitals and the medical system can actually support healthy agriculture, both through aggregate purchasing and through advocacy and policy. The clinical piece is only one slice of the pie, but there’s a lot of ways to connect health and farming. 

I also learned, from family farmers around the country that farmers are using practices, like tilling and spraying chemicals, that are destroying soil and directly destroying our health.

 ARTY: How does tilling or plowing the soil affect our health?

 DAPHNE: Tilling puts particular matter or PM10 into the air. When farmers till, there are much higher rates of asthma and allergy and chronic obstructive pulmonary disease. But tilling also destroys the unpaid workers –  the soil microbes – whose job it is to scavenge nutrients from organic matter in the soil, and pass it on to the rootlets of the plants. These nutrients then go into the plants and ultimately nourish people. We have a lot of evidence that when you lose biodiversity in the soil, you lose the nutrient value of those plants. By tilling, we are basically stealing our own nutrition.

ARTY: Is there is a relationship between a healthy soil biome and a healthy intestinal biome? 

DAPHNE: We understand the links theoretically and there are even some studies showing that the bacteria that are in the soil might influence the bacteria in our gut, but the science is not well established yet. But there are lots of plausible connections, including the fact that if you use a lot of herbicides and pesticides in the soil, they actually get transported via the food into our gut, and can kill off our own bacteria, much the same way that antibiotics do. 

But I don’t want to make false claims. You are asking about exactly the area where we need a lot more research. Unfortunately, to do that research requires human microbiologists and soil microbiologists collaborating together and asking questions that span both environments, but it is very challenging to get researchers to move outside their comfort zone and ask questions that are a little more expansive.

ARTY: There is more science that supports the idea that a healthy soil biome will deliver better minerals to the plant.

DAPHNE: Yes. Now that is something that, once again, we still need to do more research on in order to establish exactly what a healthy soil looks like. We haven’t even come to a universal definition of how to measure soil for health. What does soil health look like? The USDA’s Soil Initiative is trying to publish standards for healthy soil. Obviously, we know it’s going to look different in Kansas or in California, but at least we need some principles and some basic criteria that have to be met in order to call a specific soil a healthy soil.

We do know that plants will get a better uptake of nutrients from  a very alive, biodiverse soil with a good ratio of fungi to bacteria. That’s because the higher the diversity of these fungi and bacteria, the more likely it is that there will be the right bug to do that specific job of harvesting that nutrient and passing it on to that specific plant, kind of a lock-and-key relationship that exists. 

ARTY: What is your take on the studies comparing asthma rates of city kids and farm kids?

DAPHNE: This research is really exciting for me and it is an example of that kind of discipline-spanning research that is needed. It initially started with allergists in Germany who were trying to understand why it was that their patients, who grew up on sustainable Bavarian farms, had such low rates of asthma and eczema and even certain chronic autoimmune diseases, especially when compared to kids living in urban areas in Germany, but also compared to kids living on more conventional farms. What they found through their research was that it looked like it was the biodiversity of microbes on those farms and in the soil and in the milk and in the cowsheds and on the mattresses and everything else that seemed to make a difference. The kids on those sustainable farms were exposed to a much larger diversity of microbes. The microbes, in some way, were helping to stimulate their innate immune system. Maybe even early on when those kids were developing in utero in their moms, they were being protected. The microbes were sort of training the immune system so that it was able to distinguish friend from foe and not to overreact to allergens and so on.

Most autoimmune processes, even allergies, are just our immune system overreacting to things that it shouldn’t. It looks like having that early exposure to a diversity of bacteria really made a difference. Studies in the US have similar findings.

ARTY: More and more, there’s a growing awareness about the risks of the use of antibiotic soaps in the home. How does that relate to this conversation?

DAPHNE: Oh, it truly does. For generations people were really paranoid about germs and did everything they could to sterilize, and for with good reason. People used to die in scores from things like polio, tetanus, you name it. In the 1950s we really went overboard and started to lead unbelievably sterile lives, where we had absolutely no contact with bacteria. Everything was sealed and packaged and pasteurized and boiled and so on, which corresponds to when we started to see an uptick in a lot of autoimmune diseases.

I think what’s happening now is there is a recognition that you need a healthy profile of bacteria in your life; it doesn’t matter if you live in an urban or a rural area, you need it. There’s much more of an effort to expose kids to it, with playgrounds where they’re encouraged to play in healthy dirt, and the idea that urban farming and getting your hands in the soil, no matter where you are, is really important. 

Doctors are getting on board too and prescribing antibiotics a lot less. Of course, they’re still prescribing it for pneumonias and kidney infections and things where you absolutely need it, but we used to prescribe it for things that you’d think maybe at some point might develop into an infection, maybe. You’d send someone home with 20 days of antibiotics. It was just completely overboard. Now they’re giving shorter courses  of antibiotics that are less broad spectrum and are more specific for what’s needed. I think that there has been a big change in the medical profession.

Where there hasn’t been enough of a change is in agriculture, and we use way too many antibiotics in agriculture. We use it basically as a growth promoter in conventional agriculture for livestock and chickens and so on. There is research to suggest that a lot of antibiotic resistance in humans might be coming from agriculture. So, that is a place that still very much needs to change. I think that San Francisco is going to become one of the first cities in America to require antibiotic labeling on meat, so you’ll understand whether that meat was treated or not with antibiotics so that consumers can really demand antibiotic-free products.

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