exercise increases zinc loss from the body
(Dressendorfer & Socklov 1980; Haralambie
1981; Singh et al.1990; Clarkson & Haymes 1994)
and that levels may be low in athletes. Possible
explanations for the reduced level of zinc stores
include inadequate intake of zinc, low bioavail-
ability, increased zinc loss during exercise, dilu-
tion of zinc by expansion of plasma volume, and
redistribution of zinc in the body.
Contrary to these reports, Lukaski (1989;
Lukaskiet al.1990) has found that zinc status is
not affected by physical training as long as
dietary intakes of zinc are adequate. Lukaski et al.
(1990) studied 16 female and 13 male swimmers
and 13 female and 15 male non-swimming
controls. Plasma zinc values were within the
normal range for all subjects and did not change
throughout the swimming season. In addition to
Lukaski’s studies, Duester et al.(1989) investi-
gated the effects of endurance training on zinc
status in 13 highly trained women and compared
them with 10 untrained controls. Three-day
dietary records were evaluated for zinc intake
while blood and 24 h urine samples were taken
before and after a 25-mg oral zinc load. Mean
daily zinc intakes did not differ and were below
the recommended dietary allowance set for zinc
for both groups. The authors reported no differ-
ences between fasting concentrations of plasma
zinc, serum albumin, a-2-macroglobulin, and
erythrocyte zinc content among the two groups.
However, the trained women had significantly
(P<0.05) higher urinary zinc excretion and
reduced responses to the oral zinc load than did
the untrained women. The authors concluded
that the increase in zinc excretion in the highly
trained women may reflect higher rates of skele-
tal muscle turnover.
zinc and the vegetarian
In addition to these studies of athletes, several
studies confirm lower zinc status among
vegetarians (Freeland-Graves et al.1980; Gibson
1994; Kadrabova et al.1995).
Janelle and Barr (1995) recently reported
a study comparing nutrient intakes between
female vegetarians and non-vegetarians with
similar health practices and found that vegans
and lactovegetarians had lower zinc intakes
(8.5 and 8.2 mg · day–1, respectively) than the
recommended dietary allowance of 15 mg · day–1.
Similar results were found in a study conducted
by Donovan and Gibson (1995), who found that
33% of semivegetarians, 24% of lacto-ovovege-
tarians and 18% of omnivores had serum zinc
levels below 10.7 nmol · l–1. They also reported
that the phytate to zinc ratio in the diet was nega-
tively associated with the serum zinc concentra-
tion (P<0.05). The authors concluded that the
suboptimal zinc status was the result of low
intakes of poorly available zinc in all dietary
groups.food strategies for increasing
zinc in a vegetarian diet
Foods for the vegetarian that have the highest
zinc content are oysters, crab, shrimp, wheat
germ and legumes. Incorporating other good
sources of zinc into a vegetarian diet will also
help meet the dietary recommendations: nuts,
beans and whole grains can all contribute. Zinc is
not part of the enrichment process, so refined
flours are not a good source.Calcium requirements of vegetarians
The diets of strict vegetarians or vegans tend to
be low in calcium unless adequate amounts of
milk and dairy products or dark leafy greens
are consumed daily. As with iron and zinc, the
absorption of calcium may be reduced by phy-
tates, oxalates, fibre and tannins ( James et al.
1978; Weaver et al.1996). Phytic acid is found in
oatmeal and other whole-grain cereals, while
oxalates are commonly found in beets, spinach
and leafy greens. These binders seem to depress
absorption of calcium present in some calcium-
containing foods but not in others. That is why
strict vegans who obtain most of their dietary
calcium from leafy greens and whole-grain prod-
ucts are at a greater risk of an inadequate calcium
availability than milk-drinking vegetarians. A