Vegetarian diets can be healthy. There is no reason that animal products are required in the diet, as long as dietary practices are modified to take account of the nutrients that are normally supplied by animal products. In other words, removing animal products from a standard diet will likely lead to nutrient deficiency diseases because meat and animal products supply important essential nutrients. However, if modifications are made to the standard diet when animal products are withdrawn, such that those essential nutrients are obtained from other sources, then the diet will be healthy. Despite this obvious logic, many people who avoid animal produce and consider themselves vegetarian have not thought deeply about their diets and their nutrient intakes, and as a result many vegetarian diets are deficient in one or more essential nutrients. Animal products are a source of zinc, and animal proteins may increase absorption rates of zinc, suggesting that vegetarians may be at risk of poor zinc status.
Researchers have investigated the effects of lacto-ovo-vegetarian diets on the zinc status of non-vegetarian female subjects1. The subjects consumed a vegetarian diet containing the RDA of the known essential nutrients for 22 days. Estimates of zinc status was performed through analysis of hair, plasma and saliva. The results showed that throughout the course of the diet no differences were found in salivary or plasma zinc concentrations. However, salivary sediment, which consistent of sloughed off epithelial cells showed a 27 % decrease in zinc from initial values. Before and after the diet, plasma zinc status was assessed through administration of a 50 mg oral zinc load to 5 of the subjects. Prior to the diet, the zinc uptake in the women was related inversely to protein intake. Increased zinc uptake and increase area under the curves were observed in response to the zinc load following the vegetarian diet. Therefore as animal protein levels fell, zinc status was detrimentally affected.
The significantly increased uptake of zinc and the decreased epithelial concentration of zinc, following the vegetarian diet, suggest that zinc status was negatively affected by the diet. The authors speculated that this may have resulted from the vegetarian diet supplying high concentrations of dietary fibre. Dietary fibre may be able to bind certain minerals through its content of phytate, and this may increase elimination rates. However the crude fibre intake of the subjects on the vegetarian diet was only 7.8 grams (4638 mg of phytate), which although higher than the subject’s normal diet, is still fairly low. It is possible therefore that the high calcium content of the diet may have contributed to reduced zinc absorption. It should also be considered that the detrimental changes to zinc status observed were despite the subjects consuming the RDA for zinc. This adds weight to the contention that the RDAs are not able to prevent nutrient deficiencies, and in this respect have been criticised by nutritionists for being too low.