diet containing legumes and whole grains for 8 weeks maintained zinc status within normal limits, even though the diet was lower in total zinc and higher in phytate and fiber than a control omnivorous diet.121 To maintain adequate zinc status, the authors advised that legumes and whole grains be consumed regular- ly. Another study of women who habitually followed a plant-based diet found that adding milk and yogurt to a plant-based diet high in phytate increased zinc bioavailability by more than 70% without altering iron bioavailability.122


zinc bioavailability by reducing binding to phytic acid.2 plant foods is shown in Box 16.3.


Soaking and sprouting beans, grains, nuts, and seeds are other methods that can improve Te zinc content of selected protein-containing


Iodine Iodine status has not generally been a concern for athletes living in industrial countries. Evidence is mounting, however, that some vegetarians and vegans may be at increased risk for iodine deficiency.4,123-126 One study that assessed the iodine status of 81 nonathletic adults found that 25% of the vegetarians and 80% of the vegans had iodine deficiency (urinary iodine excretion value below 100 µg/L) compared with 9% in nonvegetarians.123


Tese studies have exposed a need for more research, looking especially at the possi- Sea salt, ko-


ble effects of iodine deficiency on the health and performance of athletes. Vegetarian athletes can ensure adequate iodine status by consuming one-half teaspoon of iodized salt in the diet daily.127


sher salt, and salty seasonings such as tamari are generally not iodized. Neither are most high-sodium processed foods. Finally, while plant foods such as cruciferous vegetables, sweet potatoes, and soybeans naturally contain goitrogens, these foods have not been associated with hypothyroid or thyroid insuffi- ciency if iodine status is adequate.128


Magnesium Suboptimal magnesium status is thought to be widespread in the United States.129


Athletes participat-


ing in sports requiring weight control (eg, wrestling, ballet, and gymnastics) are especially vulnerable to an inadequate magnesium status.7,130


Athletes participating in strenuous exercise may also be at risk due


to increased magnesium losses in urine and sweat that may increase magnesium requirements by 10% to 20%. Marginal magnesium deficiency impairs exercise performance and amplifies the negative con- sequences of strenuous exercise including oxidative stress. In athletes with suboptimal status, increased dietary intake of magnesium or magnesium supplementation will have beneficial effects on exercise per- formance.130


Foods rich in magnesium, which come mostly from unprocessed plant-based sources, are listed in Box 16.3.


B Vitamins Vegetarian diets can easily provide the requirements for most B vitamins.2,131


Diets containing little to no eggs or dairy and those low in energy, however, may not supply adequate vitamin B-12 and riboflavin.132


VITAMIN B-12 Cobalamin, the active form of vitamin B-12, is found almost exclusively in animal products.133


Vegan


athletes should, therefore, make the effort to consume vitamin B-12–fortified foods daily or take a multi- vitamin containing vitamin B-12. Food sources of vitamin B-12 include yeast flakes, soy milk and other fortified plant-based milks, breakfast cereals, and meat analogues that are vitamin B12–fortified.2


Although


some discussion in the lay literature suggests that fermented soy products and nori and chorella seaweeds can supply bioavailable vitamin B-12, research does not consistently support this concept, which arose be- cause the standard assay for determining vitamin B-12 content does not distinguish between biologically active forms and analogues.134-136


CHAPTER 16: VEGETARIAN ATHLETES 339


Te higher prevalence of iodine deficiency among vegetarians is thought to be a


consequence of prevailing (or exclusive) consumption of plant foods grown in soil with low iodine con- tent, limited consumption of cow’s milk, little or no intake of fish or sea products, and reduced use of iodized salt.123-125


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