purely vegan diet may also be low in vitamin D,
which will further impair calcium absorption
and utilization.
In an interesting anthropological study of
prehispanic burials from the Canary Islands,
Gonzalez-Reimers and Arnay-de-la-Rosa (1992)
found a high prevalance of osteoporosis among
the 117 skeletons analysed for trace elements.
Bone trace element analysis showed that low
concentrations of iron, zinc and copper were
found in skeletons with a reduced trabecular
bone mass. The authors state that during this pre-
hispanic period many of the residents of the
Canary Islands existed in a relative protein-
energy malnutrition state which consisted
mainly of a vegetarian diet which may have pre-
disposed these individuals to osteoporosis.
It has been suggested that vegetarians who
restrict their intake of dairy products should
provide calcium-rich foods or supplements by
consuming calcium-fortified soy products as
well as consuming dark leafy green vegetables
on a daily basis.
food strategies for increasing
calcium in a vegetarian diet
Foods with the highest nutrient density for
calcium are leafy greens, such as spinach and
broccoli, non-fat milk, romano cheese, swiss
cheese, sardines and canned salmon. The
calcium found in some leafy greens is not well
absorbed because of the presence of oxalic acid,
but this effect is not as strong for kale, collard,
turnip, and mustard greens. Overall, non-
fat milk is the most nutrient-dense source of
calcium because of its high bioavailability and
low energy value. The new calcium-fortified
orange juices and other beverages offer an alter-
native to the individual who is a strict vegetar-
ian; other calcium-fortified foods include bread,
breakfast cereal, breakfast bars, and snacks.
Another good source for the vegetarian is
soybean curd (tofu) if it is made with calcium car-
bonate (check the food label).
While there are concerns about the potential
lack of some nutrients in a vegetarian diet, many
450 special considerations
of these concerns can be overcome by using a
wide variety of foods and planning meals so that
they complement proteins and include nutrient-
dense foods. Table 33.3 summarizes the nutrients
that may be lacking in a vegetarian diet and
gives some examples of foods that could be in-
cluded in a vegetarian diet to overcome these
inadequacies.Hormonal alterations as a result of
a vegetarian diet
There is evidence that nutritional status and diet
can affect the reproductive system. Hill et al.
(1984) found that Caucasian women (n=16), who
normally ate meat had a significantly (P<0.01)
shorter follicular phase of their second menstrual
cycle when they ate a vegetarian diet for two
cycles. The vegetarian diet decreased (P<0.01)
the pituitary response to releasing luteinizing
hormone and decreased (P<0.05) the episodic
release of luteinizing hormone. The experiment
also included supplementing nine vegetarian
Black South African women with daily meat
product: an increased length of the follicular
phase was observed (P<0.01). The authors
concluded that a lower episodic release of
gonadotrophins and a shorter duration of the
follicular phase, when omnivorous women ate
no animal protein, implies that a vegetarian diet
plays a role in the control of ovulation through
the hypothalamic axis of the central nervous
system. In a similar study, Pirke et al.(1986)
investigated the influence of a vegetarian diet
on the menstrual cycles of 18 healthy normal
weight women aged 17–27 years. Plasma levels
of oestradiol, progesterone and luteinizing
hormone were measured on Monday, Wednes-
day and Friday throughout the 6-week diet
period. Nine women followed a vegetarian diet
while nine followed an omnivorous diet. Both
groups lost weight during the experimental
period (1 kg body weight · week–1). Seven of the
nine vegetarian women became anovulatory and
had significantly decreased luteinizing hormone
during the mid-cycle and luteal phase. Oestro-
gen and progesterone levels were also signifi-