Presentacion

Declining Fruit and Vegetable Nutrient
Composition: What Is the Evidence?
Donald R. Davis1,2,3
Biochemical Institute, The University of Texas, Austin, TX 78712; and Bio-Communications
Research Institute, 3100 North Hillside Avenue, Wichita, KS 67219
Additional index words. nutritive value, history, dilution effect, genetic dilution effect, agriculture, grains
Abstract. Three kinds ofevidence point toward declines of some nutrients in fruits and vegetables available in the United
States and the United Kingdom: 1) early studies of fertilization found inverse relationships between crop yield and mineral
concentrations—the widely cited ‘‘dilution effect’’; 2) three recent studies of historical food composition data found
apparent median declines of 5% to 40% or more in some mineralsin groups of vegetables and perhaps fruits; one study also
evaluated vitamins and protein with similar results; and 3) recent side-by-side plantings of low- and high-yield cultivars of
broccoli and grains found consistently negative correlations between yield and concentrations of minerals and protein, a
newly recognized genetic dilution effect. Studies of historical food composition data areinherently limited, but the other
methods can focus on single crops of any kind, can include any nutrient of interest, and can be carefully controlled. They can
also test proposed methods to minimize or overcome the diluting effects of yield whether by environmental means or by
plant breeding.

This article summarizes three kinds of
evidence pointing toward declines during the
last 50 to100 years in the concentration of
some nutrients in vegetables and perhaps also
in fruits available in the United States and the
United Kingdom.
INVERSE RELATIONS BETWEEN
PLANT YIELD AND MINERAL
CONCENTRATION
This article summarizes three kinds of
evidence pointing toward declines during the
last 50 to 100 years in the concentration of
some nutrients in vegetables and perhaps also
infruits available in the United States and the
United Kingdom. It has been noted since the
1940s that yield increases produced by fertilization,
irrigation, and other environmental
means tend to decrease the concentrations of
minerals in plants. Jarrell and Beverly (1981)
reviewed the evidence for this well-known
‘‘dilution effect.’’ Although their review has
been cited over 180 times (60 timesfrom
2000 on), few mentions of the dilution effect
contain a reference, suggesting that the effect
is widely regarded as common knowledge.
Citations to the review are diverse, involving
(in descending order), grains, fruits and
vegetables, trees and shrubs, legumes, pasture
plants, and flowers. The most commonly
cited fruits and vegetables are tomatoes,
potatoes, taro, onions, peppers,and berries.
Jarrell and Beverly cited the example of
red raspberry plants grown in soil with 12
ppm of phosphorus (P) and fertilized with
additional amounts of 0, 22, and 44 ppm P
(Hughes et al., 1979). After 8 months, plants
grown with 44 ppm of added P had _20%
higher concentration of P than unfertilized
plants (dry weight basis). However, the concentrations
of all eight other measuredminerals
declined, usually by 20%to 55%(Fig. 1).
Fertilization produced large increases in
plant dry matter, 37% at 22 ppm and 119%
at 44 ppm. Thus, the fertilized plants contained
larger absolute amounts of minerals
than the unfertilized plants, but these
amounts were sufficiently diluted by the
increased dry matter that all mineral concentrations
declined, except for P.
APPARENTNUTRIENT DECLINES
IN HISTORICAL FOOD
COMPOSITION DATA
There are three quantitative reports of
apparent median or average declines of
nutrients in groups of vegetables or fruits
(Davis et al., 2004; Mayer, 1997; White and
Broadley, 2005). The groups of foods usually
numbered from 20 to 45. All authors calculated
ratios of nutrient contents, R = new/old,
for each food and nutrient, where the...