Loss of Edible plant diversity in today’s diets
Walking into an American grocery store can be overwhelming—a veritable immersion in abundance. This abundance, however, belies a relative paucity of nutrient diversity in today’s food, compared with the food of our ancestors.
Edible plants—then and now
Before the days of sophisticated agriculture, human beings ate plant foods that grew wild, or were cultivated on a small scale. This meant a diet that was low in calories but inclusive of a wide array of different plants. In contrast, today, a small number of plants optimized for agricultural yield and other qualities have come to dominate our diet. To give an idea of how extreme this constriction is, consider that, of the ~30,000 edible plant species, 7,000 are currently being used for food, but only about 150 are being cultivated. Most of these are each eaten by just a small fraction of the global population. In addition, 75% of all human food is provided by just 12 plants, according to the UN’s Food and Agricultural Organization (FAO), and about half of the human food supply comes from just three plants: rice, maize (corn), and wheat. These plants are energy-rich, so they do a great job of preventing starvation, but a diet largely based on them might be micronutrient poor.
Beyond the relatively few types of food plants making up our diets, the varieties within each plant type have also been severely constricted. For most of today’s commonly eaten vegetables, just a few varieties, optimized for efficient, large-scale production, are available. For example, seed houses a century ago offered over 300 varieties of sweet corn. Today’s seed houses offer only 12 varieties. The graphic below is courtesy of the Rural Advancement Foundation International-USA, http://rafiusa.org.
With 75% of crop biodiversity lost from today’s fields, governments are scrambling to at least preserve the genes of heirloom crops through seed banks. Even if the seeds are preserved, though, these varieties will not be showing up in markets any time soon. Often kept in vault-like conditions designed to withstand war, climate change, and natural disasters, they are not easily available for cultivation. On a practical level, the vast wealth of food crops cultivated in the past has essentially been lost to today’s farmers.
Increased yield, decreased nutrition
As agriculture and food science have steadily grown, plants that are optimized for agricultural yield have come to dominate our diet. These plants are easy to grow and have some beneficial qualities for the consumer, such as sweetness, but many lack the diverse micro-nutrients humans used to consume. For example, one powerful component of a healthy diet is the polyphenols, a class of micro-nutrients that have antioxidant properties and support the microbiome. Through this support, the polyphenols benefit human health in a myriad of ways, including maintenance of healthy blood glucose levels, protection against cancer, and aid in maintaining a healthy weight.
The health consequences of reduced diversity
Reliance on only a few food plants causes tragic malnutrition-related illness in developing countries. For example, every year, hundreds of thousands of children go blind due to vitamin A deficiency because their diets consist almost exclusively of rice, a poor source of vitamin A. While molecular biologists have engaged in an international effort to engineer strains of rice that are high in vitamin A, this effort has spanned decades and cost large sums of money. While commendable as a practical innovation that could prevent blindness in millions of children, this rice will still only restore a single nutrient—albeit an important one– to a nutrient-poor diet. In contrast, foods closer to nature are both easy to cultivate and capable of providing several nutrients. For example, dandelion, so easy to grow that it is generally considered a weed, is rich not only in vitamin A but also vitamin C, and contains more iron and calcium than spinach.
In the developed world, eating a diverse diet should be easy. Not only do we have access to wild foods like dandelion greens, but we also have the resources to demand diverse cultivated foods as well. Unfortunately, the actual demand tends to go the other way—American shoppers are more likely to choose convenient, familiar produce (when even choosing fresh produce over processed foods). This tendency leads to a self-perpetuating loop of fewer types of food being chosen by most consumers leading to fewer choices for those consumers pursuing a more diverse diet. Despite a general state of food abundance and emphasis on choice in the U.S., most Americans only have access to food plants in at most two or three micro-nutrient-poor varieties. (When was the last time you saw Purple Peruvian potatoes in the supermarket?!) In contrast to the severe nutrient deficiencies seen in the developing world, the consequences of constricted food diversity in developed countries are not dramatic. Instead, they are slow, subtle, and insidious, contributing to chronic illnesses like obesity, diabetes, and cancer.
On the other hand, the growing awareness of the microbiome and its importance to long-term health may very well spark an increase in demand for diverse plant foods. Variety in high-quality American supermarkets is steadily increasing, and while plant food diversity may be low compared with 500 years ago, it has increased substantially compared with 50 years ago. A growing interest in farmers’ markets and seasonal, heirloom vegetables may very well be the sign of a greater appreciation for food diversity, and the vanguard of a movement towards a healthier diet for the future.
References and Further Reading
A healthy gastrointestinal microbiome is dependent on dietary diversity. Heiman ML, Greenway FL. Mol Metab. 2016 Mar 5;5(5):317-20.
Linking biodiversity, diet and health in policy and practice. Johns T, Eyzaguirre PB. Proc Nutr Soc. 2006 May;65(2):182-9.
Science and society: protecting crop genetic diversity for food security: political, ethical and technical challenges. Esquinas-Alcázar J. Nat Rev Genet. 2005 Dec;6(12):946-53.
Functional traits in agriculture: agrobiodiversity and ecosystem services. Wood SA, Karp DS, DeClerck F, Kremen C, Naeem S, Palm CA. Trends Ecol Evol. 2015 Sep;30(9):531-9.
What is Happening to Agrobiodiversity? Food and Agriculture Organization
of the United Nations, 2004
Antioxidant Polyphenols and the Microbiome. Copeland CS, Heiman M. Feb. 2018.
Micronutrients. National Cancer Institute.
Rural Advancement Foundation USA. Press releases and media coverage related to sustainable farming.
Published: May 9, 2018