Evidence suggests that the modern Western diet is devoid of meaningful levels of certain minerals. In particular zinc, selenium and magnesium have been identified in research. Mineral intakes are falling because the traditional whole food diets are being replaced by processed and refined foods that are devoid of nutrients. Refining of grain is particularly problematic because the process involves stripping away the bran and germ, both of which are the main mineral sites in grains. The result is that over the course of the last 100 years, mineral intakes have fallen and this has resulted in an increased prevalence of Western lifestyle disease. Zinc deficiency is common in Western nations which is concerning because the mineral is required as a co-factor for many enzymes including superoxide dismutase, alkaline phosphatase, carbonic anhydrase III, AMP-deaminase, lactate dehydrogenase and alcohol dehydrogenase. Zinc has important roles in immune defence and energy metabolism.
The current recommended daily intake for zinc is about 15 mg, but studies show that many do not receive this amount. For example, one study published in the American Journal of Clinical Nutrition1 investigated the zinc status of health women. Subjects included 10 women who were untrained and 13 women who were highly trained athletes. Analysis of the 3 day daily diet records supplied by the subjects showed that neither group of subjects were receiving the recommended intake for zinc (assuming the foods in the tables actually contained the zinc recorded). The untrained group of women had a mean intake of 5.9 mg per day zinc, whereas the highly trained women has a mean intake of 5.5 mg per day zinc. Urinary losses were also assessed and these were significantly higher in the highly trained women when compared to the untrained women, which may reflect higher rates of muscle and bone turnover.
This would suggests that the highly trained women had a relatively poor zinc status, because although they had similar intakes, their losses exceeded those of sedentary women. It may be that the increased losses were compensated for by increased absorption rates. However, when the authors administered a zinc tolerance test to the subjects using an oral zinc supplement, they found that the highly trained women had a significantly lower plasma response in terms of area under the curve and peak values, when compared to the untrained women. The mean plasma levels of both groups of women (11.5 µmol/L) was below the mean values reported by other researchers, emphasising the poor zinc status of the subjects. Exercise is known to increase requirements for zinc, and it is likely that individuals engaged in high intensity training may require higher intakes of zinc than can be found in modern food.
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