Exploring soil health and human health

What is the link between healthy soils, and healthy food?

Unfortunately, the nutrient levels in most foods have declined in recent decades. But there is growing evidence that farming systems that build soil health can also improve human and animal health. 

Our recent cropping case study farmers Josh and Peri McIntosh (SA), Russell Young (QLD), Bruce Maynard (NSW) and Rob Hetherington (WA) are all implementing practices that aim to improve landscape health and promote diversity. They were curious to learn more about these connections and the nutrient content of their grains, so we worked with a nutritionist who set up a preliminary study.

While the scope of the study was small and limited, the results are promising and provide some indications of the potential benefits of understanding more about the links between farming and nutrition.  

Trending decline of nutrient density

Foods that are nutrient dense (ratio of nutrients to calories/energy) can contribute more macro and micro nutrients to our daily diet – or in the case of food destined for animal feed – an animal’s diet. Yet, the nutrient levels in most foods have declined in recent decades. This means that even when food is plentiful, nutrition deficiencies can still exist.

We don’t yet have clear conclusions on why this is the case, but one explanation is that our foods are nutritionally depleted due to the ‘dilution effect’ and our focus on quantity rather than quality – an increase in the size of a food product results in the product having fewer nutrients per gram (Montgomery and Bikle 2023). Other researchers have suggested that nutrient deficiencies could result from minerals being present in the soil, but not available in a form that plants can access. Of course we need to understand what’s in our soils in the first place to know the potential cause of deficiencies.

Some studies suggest farming practices such as intense tillage, nitrogen fertilisation, and synthetic pesticide application have contributed to a decline in nutrient density by disrupting the relationships between crops and the soil microbiome (Montgomery and Bikle 2023). Conversely, crops and livestock produced using practices that support soil health are more nutrient dense (Montgomery et al. 2022)

How do nutrients get into our food?

The relationship between soils, plants and nutrition is complex. Soils play a crucial role in providing the necessary nutrients for plant growth and development, which in turn affects the nutritional content of the plants themselves, and the nutrients available for humans and animals to consume. 

Soils are composed of minerals, water, air, organic matter and microorganisms. These components interact to create a dynamic environment that influences nutrient availability to plants. Plants obtain nutrients from the soil through various mechanisms that involve physical, chemical and biological processes.

Plant rhizospheres (root zones) play an important role in the way nutrients enter our food chains. There is a hive of activity in this zone where plants and microbes are in co-beneficial relationships. Plants release a variety of substances from their roots into the soil which support nutrient cycling and ecosystem function. These substances, also known as root exudates, are complex mixtures of organic compounds such as sugars, amino acids, organic acids, enzymes, hormones, and secondary metabolites that serve multiple functions, including nutrient acquisition. 

Microbes collect nutrients in the soil, and nutrients are extracted from microbes in the cells of plant roots, which increase the availability of the minerals and trace elements required to maintain the health and vitality of their plant hosts. (Learn more about this area of microbial research called the rhizophagy cycle here).

Insights from a preliminary study

We worked with our cropping farmers to collect grains, including oats, wheat, rye, lupins, canola, forage sorghum, and multispecies mixes, and the nutritionist sent them to the authorised food testing laboratory Agrifood Technology to be tested for:

• Nutrition components: protein, carbohydrates, fat, saturated fat, (required for food labelling) monounsaturated fat, polyunsaturated fat, trans fat, energy, ash, moisture, nitrogen, total dietary fibre
• Essential minerals: aluminium, calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, zinc, selenium
• Starch: (for one case study farm ‘Willydah’ only) due to end use of wheat for baking purposes.

The nutritionist then interpreted the results in relation to a reference sample taken from Food Standards Australia New Zealand (FSANZ), a statutory authority in the Australian Government Health portfolio. There are limitations to the results due to variations in grain storage, and appropriate reference samples for the companion and multispecies mixes.  With the limitations and scope of the study in mind, the results were still promising, and showed a few trends across the four farms.

Dietary fibre

Dietary fibre was consistently high across all farms in comparison to the reference sample, with one wheat sample from Josh and Peri’s farm being almost 60% higher (18 g/100 g compared with 11.4 g/100 g for the whole wheat FSANZ reference sample). And Willydah oat samples were more than 30% higher in dietary fibre compared to the reference sample. 

In Australia, a major portion of our dietary fibre comes from breads and other cereals (National Nutrition Survey, 1995), totalling around 45%. Recommended nutrient uptake levels for dietary fibre for average men and women are 30 g/day and 25 g/day, respectively (not including lactating adults, children and adolescents). The overall population health benefits of high dietary fibre are well known, with the presence of fibre in grains assisting in slowing the process of transforming starch to glucose in the body. This can assist the body in maintaining a steady blood sugar level. 

There are potential opportunities to grow industry and consumer awareness and increase market reach through value-adding into sectors seeking good sources of dietary fibre, for example: 1) ingredient buyers; 2) food manufacturers seeking premium grain; 3) premium processed and packaged foods sectors; and 4) the aged care sector where nutrient dense portion-controlled foods are in high demand. 

Fats

There were higher results in poly and monounsaturated fats across most farms, indicating the presence of omega-3 and omega-6 fatty acids. These fats are essential in the diet and cannot be made by the body. Omega-3s play an important role in the body, helping protect against heart disease, stroke and various other health related problems. Omega-6s also have a positive role to play in the body and have been shown to reduce the risk of heart disease when substituted for saturated fats in the diet. 

Rob’s wheat and multispecies samples had higher results for poly and monounsaturated fats in comparison to the FSANZ reference sample. Rob’s multispecies grain goes to a dairy, and the dairy’s own records reinforced our nutrition results, showing a grain lipid content of 4.4% (compared to 1.4% in 2021). The dairy also noted an increase in the quantity of milk, without compromising protein and butterfat. They also noted an overall improvement in animal health indicated by lower somatic cell count leading to lower levels of mastitis.

Protein

A few of the farms had higher levels of protein than the reference samples. Two samples of Russell’s forage sorghum were tested (one grown in a multispecies environment and one grown in a monoculture environment) and were shown to have higher protein compared against FSANZ sorghum (8.2 g/100 g). The forage sorghum grown in the multispecies environment had 4% higher protein (13.2 g/100g) than the monoculture (12.7 g/100g), and 61% higher than the FSANZ reference sample. This is significant given that globally many communities rely on millets or sorghum grains as a dietary staple, and a growing share of the population is including these grains in their diet.

Minerals 

Of the twelve essential minerals tested, four had higher values than the reference sample: zinc, potassium, phosphorus, and for the oat sample, calcium. The zinc results are particularly interesting. Recommended Daily Intake (RDI) of zinc for the average aged woman is 8 mg/day and men 14 mg/day. Cereals, such as wheat and oats assist in contributing a substantial amount of zinc to the diet.  Bruce’s wheat grain samples are notably high in zinc, and the oat samples were equal to the reference sample. Josh and Peri’s wheat and rye samples were notably high in zinc, when compared to the reference samples. This is noteworthy because zinc is not typically a mineral that is abundantly available in many Australian soils, and hence potentially low in wheat grain nutrition. Further studies and conversations with the farmers could help to understand what management practices may be influencing this result. 

Russell’s potassium levels were high (highest 370 mg/100 g) across four wheat samples when compared to the FSANZ reference samples (315 mg/100g). Potassium results for the three of Rob’s wheat samples were also high at 350-400 mg/100 g. Potassium is an important mineral that functions as an electrolyte and helps regulate fluid balance, nerve signals and muscle contraction.

Of the other minerals tested, some levels were the same as, slightly lower, or significantly higher. However, none of the samples had nutrient levels that were overly high (toxic levels) or overly low. 

Where to next

This preliminary study provides some interesting indicative results in what is an emerging area of research. More work is needed to collect better reference data that covers a wider scope of nutrient components, and where the farms and types of practices are part of the research method.

Other potential areas for further research include measuring phytochemicals in grains; comparing the nutrient content of different wheat varieties; refining a method for testing multispecies/mixed crops; the relationship between soil biological and fungal communities and nutrition; as well as more baseline data (on a farming systems basis) comparing crops produced through synthetic input heavy systems and those produced in regenerative systems.

Expanding research may help to better understand the potential public health (and environmental) advantages of farming approaches that build soil health, and support the development of policy and markets that support farmers to adopt these approaches and deliver the most nutritious food to their customers. 

Listen to our podcast on nutrition 🔊

We’ve all heard the saying “You are what you eat”. But, as we hear in this episode, it really should go “You are what you eat, and the soil it grows in.”

Over half of our adult population are considered to be malnourished, and this is in part due to a decline in the nutrient density of our food. As the world’s population grows and remaining arable land decreases, growing healthier, nutrient dense food might just be a part of the answer to improving human health outcomes.

In this episode we talk with two farmers and two researchers about the question: ‘Is soil the key to better human health?’.

What we find is a complex tangle of connections between soil, plants, animals, and humans that science is only just beginning to understand.