Nutrient Quality of Food Affected by Agricultural Practices
Dr. Debra Pearson’s presentation at NEWfare focused on how agricultural practices influence the nutrient content of the fruits and vegetables we grow and the livestock we raise. An examination of the USDA’s food database since the 1950s indicates that there has been a decline in some nutrients over a range of fruits and vegetables.1 There are still many unanswered questions and controversies about why there has been a decline in the nutrient content of produce, but research suggests 3 reasons for this decline: 1) monoculture farming, 2) selection for yield, and 3) plant defenses. Techniques of plant breeding, selection and genetic modification, fertilizer, pesticide and herbicide practices, crop and livestock management differ markedly between sustainable/organic farming and industrial farming, and these differences impact the nutrient profiles of crops and livestock.
For a number of reasons relating in part to uniformity of produce to make machine planting and harvesting easier, the varieties of any given crop grown has sharply declined over the decades. We used to grow many more varieties of apples, corn, potatoes, broccoli etc, but in recent decades for most of these crops we have drastically decreased the number of varieties. One of the basic tenants of good nutrition is “variety”. The greater the variety of foods in our diet the better our chances for obtaining the wide array of nutrients we need. The minute we reduce the variety of foods, it becomes harder to obtain the full range of needed nutrients. Along with a reduction in the variety of crops grown, industrial farming has emphasized yield – selecting and breeding plants for bigger yields. Scientists theorize that plants have a somewhat fixed amount of resources, and if the plant is bred to grow rapidly and/or produce larger fruit (more dense head size in the case of broccoli) then the plant has fewer resources to direct to vitamin synthesize or mineral acquisition, thus nutrient density is compromised. We have seen this happen for instance, in the wheat cultivars we grow. We have both reduced the variety of wheat cultivars grown and selected for larger wheat yields. This then has reduced the mineral content of several minerals in the modern wheat cultivars grown versus the historical varieties that used to be grown.2
Plants synthesize a wide variety of phytochemicals (over 8000 have been identified) that protect plants from viruses, fungal diseases, UV/oxidative damage, and help in plant growth and maturation. Humans obtain these important beneficial phytochemicals when we eat plants. Also, livestock – if allowed to graze in the fields – obtain these phytochemicals as well, which means their meat, eggs, and milk are enriched with these phytochemicals. Industrial farming, with its heavy reliance on pesticides and fertilizer practices that don’t support the maintenance of a rich organic soil matrix seem to dramatically decrease the amount of phytochemicals the plants produce.3,4
What we feed livestock directly impacts the nutrient and phytochemical content of the meats, milk and eggs we eat. Grass-fed cattle and free-range chickens produce milk and eggs that are lower in overall fat content, higher in omega-3 fatty acids, higher in conjugated linoleic acid, higher in vitamins such as vitamin E and higher in phytochemicals. To reverse the decline and increase the nutrient density of foods, Dr. Pearson concluded that we need to research, develop, and encourage the use of agricultural practices that promote high quality, nutrient dense foods.
Davis et al J Am Coll Nutr, 2004, 23, 669
Murphy et al Euphytica, 2008, 163, 381
Wang et al JAFC, 2008, 56, 5788
Mitchell et al JAFC, 2007, 55, 6154