Concerns about decreasing nutrient density in American foodstuffs have circulated for years. Perceived causes for the diminished nutritional state of our foods include a trend toward industrial farming, the leaching of agricultural soils, poor crop rotation methods, and development of crops that – while more amenable to mass production – do not provide the nutrients found in traditional cultivars. (Jack, A. Nutrition under siege. One Peaceful World (Kushi Institute Newsletter), Becket, MA, Spring 1998, pp 1, 7–8 and Long C: Is chemical farming making our food less nutritious? Organic Gardening. Nov/Dec 1999, p 12 )
American eating patterns have also changed over the past 50 years. With shifts from agrarian to urban lifestyles, most people have acquired the habit of buying food from stores…and their dietary choices often include more prepared and processed items than fresh produce. (Nutrition and Your Health: Dietary Guidelines for Americans. 5th Edition. U.S. Department of Health and Human Services and Agriculture, 2000)
Evidence for Declining Nutrient Levels in Vegetables
In a 2004 study that compared data collected in 1950 and 1999, researchers evaluated the levels of 13 nutrients in 43 foods – including 39 vegetables, 3 melons, and strawberries – that are commonly grown in home gardens.
The scientists selected foods that were included in the USDA’s Nutrient Database in both 1950 and 1999, striving to select foods that were described identically in both databases. They carefully adjusted nutrient data for confounding factors (e.g., differences in water content and dry matter) before applying a statistical analysis to nutrient levels.
The studied nutrients included ascorbic acid (vitamin C), riboflavin, niacin, thiamin, vitamin A, iron, phosphorus, calcium, carbohydrate, fat, protein, ash content (a reliable measure of major minerals), and fiber. Water content was also determined.
Representative changes in nutrients from foods grown in 1999 versus those grown in 1950 include:
- A 38% decrease in riboflavin
- A 15% decrease in ascorbic acid
- A 16% decrease in calcium
- A 9% decrease in phosphorus
- A 15% decrease in iron
- A 6% decrease in protein content
- A slight increase (0.6%) in water content
- There were no statistically significant differences in vitamin A, thiamin, niacin, fat, or carbohydrate content
The authors of this study commented that their findings were nearly independent of random source errors, but there may have been other confounding factors:
- Sampling: geographic or seasonal sampling may have differed between analytic periods; more crops were grown in home gardens in the mid-1900s; international sources now compose a larger proportion of foodstuffs consumed in the U.S.
- Differences in cultivars: production farming mandates the selection of varieties that are chosen for yield, disease resistance, and hardiness, rather than nutrient content.
- Analytical methods: newer methodologies lead to less contamination and, possibly, different yields for a given nutrient.
- Production factors: changes in climate, differences in distribution and transport methods, and changes in location of production may confound results.
(From Davis D, Epp M, Riordan H. Changes in USDA food composition data for 43 garden crops, 1950 to 1999. J Am Coll Nutrition. 2004;23[6]:669-82)
Implications of Decreasing Nutrient Levels in Fruits and Vegetables
Although a great deal of controversy surrounds the reasons for the apparent loss of nutrients from food crops (the leaching of soils; changing patterns of harvesting, storage, and distribution; cultivar selection, etc.), the debate is overshadowed by a more compelling issue: Americans have largely eliminated fresh produce from their diets.
On average, Americans derive well over half of their calories and fiber from sugars, white flour and rice, and separated fats and oils. These staples exhibit far more significant nutrient deficits than the foods mentioned in Davis’ study.
The American diet – as is the case in most developed countries – is more nutritionally compromised from the consumption of processed foods than it is from declining nutrient levels in fruits and vegetables. (United States Department of Agriculture, Agricultural Research Service: USDA Nutrient Database for Standard Reference, Release 13, 1999)
Therefore, for those who are concerned about the nutritional inadequacy of available foodstuffs, a more productive approach (aside from tossing down a vitamin pill) would be to eliminate foods that are known to be poor nutrient sources and eat more fruits, vegetables, grains, nuts and legumes.
Even at their worst, today’s whole plant foods are still superior to many of the things Americans currently consume.
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