Effect of vegetarian diets on zinc status: a systematic review and meta‐analysis of studies in humans

Abstract

Plant-based diets contain less saturated fat and cholesterol and more folate, fibre and phytochemicals than omnivorous diets, but some micronutrients, especially zinc, are poorly bioavailable. The findings of studies exploring the zinc intake and zinc status in populations that habitually consume vegetarian diets are inconsistent. This study aims to investigate the effects of plant-based diets on dietary zinc intake and status in humans using systematic review and meta-analysis techniques. Thirty-four studies were included in the systematic review. Of these, 26 studies (reporting 48 comparisons) compared males and/or females consuming vegetarian diets with non-vegetarian groups and were included in meta-analyses. Dietary zinc intakes and serum zinc concentrations were significantly lower (-0.88 ± 0.15 mg day(-1), P < 0.001 and -0.93 ± 0.27 µmol L(-1), P = 0.001 respectively; mean ± standard error) in populations that followed habitual vegetarian diets compared with non-vegetarians. Secondary analyses showed greater impact of vegetarian diets on the zinc intake and status of females, vegetarians from developing countries and vegans. Populations that habitually consume vegetarian diets have low zinc intakes and status. Not all vegetarian categories impact zinc status to the same extent, but a lack of consistency in defining vegetarian diets for research purposes makes dietary assessment difficult. Dietary practices that increase zinc bioavailability, the consumption of foods fortified with zinc or low-dose supplementation are strategies that should be considered for improving the zinc status of vegetarians with low zinc intakes or serum zinc concentrations at the lower end of the reference range.

Position paper on vegetarian diets from the working group of the Italian Society of Human Nutrition

“…Plasma zinc levels were lower in these women than in non-pregnant women, suggesting that zinc nutritional status is influenced more by pregnancy than by LOV/ OMN diet [191]. Nevertheless those on a VEG diet have lower zinc intake [192] and lower zinc plasma levels [101] than those on a LOV diet.…”

Iron and Zinc Nutrition in the Economically-Developed World: A Review

“…Given this disparity, it is unsurprising that a recent meta-analysis found zinc intakes and zinc status to be lower among males and females following a vegetarian diet compared to those who consume meat [21]. The iron content of the foods in Figure 1 are more comparable, with animal-derived foods containing 0.64% less iron than unfortified plant-derived foods (mean 3.0 mg vs. 3.1 mg).…”

Zinc and Dietary Fibre: Competing Nutrients in the Management of Chronic Diseases

“…We investigated the effects of plant-based diets on zinc status and showed that dietary zinc intakes and serum zinc concentrations were significantly lower in populations that followed habitual vegetarian diets compared to non-vegetarians. Secondary analyses revealed greater impact of vegetarian diets on the zinc status of females, vegetarians from low-and middle-income countries (LMIC), and vegans [8,9]. Although not all vegetarian diets impact zinc status to the same extent, populations that habitually consume vegetarian diets with high PA:Zn molar ratios have a requirement for dietary zinc that is substantially greater than the amount recommended for omnivores.…”