Micronutrient Status in Vegetarians, Vegans and Omnivores
Whether to follow an omnivorous, vegan or vegetarian diet is one of those hot-button issues, with fierce proponents on both sides. Omnivores claim that their diet is better as it is less likely to lead to deficiencies in nutrients such as iron, calcium and vitamin B12, which can be of concern in vegan diets especially, while vegans point to the lower saturated fat and higher fiber and vitamin C intakes in their diets, and state that they are beneficial in preventing chronic disease and increasing life span (see review from Singh, Sabate and Fraser on how low meat intake could affect longevity). While the jury is still out on whether cutting out all animal products can help us live longer, a group of researchers lead by Schüpback recently compared the diets and nutritional status of 200 Swiss omnivores, ovo-lactovegetarians and vegans to see whether there are differences in intakes and rates of deficiency in a large number of micronutrients.
The subjects, 100 omnivores, 53 ovo-lactovegetarians, and 53 vegans, visited the research site where a blood and urine sample was taken for the assessment of vitamin and mineral status. A weighed three-day food record was completed over three non-consecutive days including one weekend. The mean micronutrient status and proportion deficient were calculated for each dietary group, as well as dietary intakes and proportion with an inadequate diet.
Magnesium: Vegans had the highest magnesium status, while there was no difference between ovo-lactovegetarians and omnivores. No vegans were deficient, while 2-4% of the other groups were deficient. Magnesium intakes were highest in vegans, followed by vegetarians and omnivores.
Iron: While hemoglobin levels did not differ between the groups, serum ferritin levels (a measure of iron stores) was highest for omnivores, then ovo-lactovegetarians. The proportion with low iron stores did not differ. Even so, vegans had the highest intakes of iron, double that of omnivores. Their lower status despite higher intakes is explained by the lower bioavailability of iron from plant sources.
Zinc: Levels were highest in omnivores, and almost half of vegans were deficient, compared to 19% of ovo-lactovegetarians and 10% of omnivores. Zinc intakes did not differ by diet.
Iodine: Mean urinary iodine concentrations were lower in vegans, and a higher proportion of vegans had low iodine, however these differences were not significant due to great variation in iodine concentrations.
Vitamin A: Vitamin A concentrations were highest in omnivores and significantly lower in vegetarians and vegans, and beta-carotene concentrations were non-significantly higher in vegans. There was no difference in the rate of deficiency or vitamin A intakes between the three groups.
Vitamin E: Vitamin E concentrations were lower in the vegetarian diet groups, but this did not change the rate of deficiency. Vitamin E intakes were significantly higher in vegans than vegetarians, and higher in vegetarians than omnivores.
Vitamin C: Vitamin C status was significantly higher for ovo-lactovegetarians and vegans. Even though a greater proportion of omnivores had a low vitamin C status, this was not significantly different from the other groups. The vitamin C intakes of vegans were significantly higher than vegetarians, who had higher intakes than omnivores.
Vitamin B1: Even though the vitamin B1 status of vegans was highest, there was no clinical deficiency in any group. Vegans had significantly higher vitamin B1 intakes than the other groups.
Vitamin B2: There were no significant differences seen in vitamin B2 status, rates of deficiency or intakes between the groups.
Niacin: Niacin status was greatest in omnivores, although there was no significant difference in rate of deficiency. Niacin intakes were lowest in ovo-lactovegetarians.
Vitamin B6: Vitamin B6 status was lowest on ovo-lactovegetarians, who had a higher rate of deficiency. Vegans had the highest intake of vitamin B6.
Vitamin B12: There was no significant difference in vitamin B12 status between the groups, although vegans had the lowest status intakes and highest rate of deficiency. Vitamin B12 intakes varied significantly between the groups, with omnivores having the highest intake, followed by ovo-lactovegetarians and then an almost negligible intake in vegans. The lack of deficiency despite almost non-existent intake is perhaps explained by the median time following a vegan diet, which was only 3 years: vitamin B12 stores are in the range of 2-5 years in a free-living population (Doets). The use of supplements in the vegan group may have improved status (43% of vegans reported use of supplements containing vitamin B12).
Folic acid: Folic acid concentrations were highest in vegans, and vegans and ovo-lactovegetarians had a significantly lower rate of deficiency than omnivores. Folic acid intakes were highest in vegans, presumably due to their consumption of green, leafy vegetables.
Pantothenic acid: There was no significant difference in blood levels of pantothenic acid, however vegans and vegetarians had higher rates of deficiency. Intakes of pantothenic acid were higher in vegans.
This report shows that the intakes of some nutrients is affected by whether people are omnivores, ovo-lactovegetarians or vegans. Even so, omnivores only had a significantly reduced prevalence of zinc, vitamin B6 and pantothenic acid compared to either of the vegetarian dietary groups, and an increased risk of folate deficiency . Clearly, the diets were nutritionally adequate in general. The total micronutrient content of the diet is more important than whether the nutrients come from meat or plant foods.
Schüpbach R, Wegmüller R, Berguerand C, Bui M, Herter-Aeberli. Micronutrient status and intake in omnivores, vegetarians and vegans in Switzerland. Eur J Nutr. 2015 Oct 26. [Epub ahead of print] http://www.ncbi.nlm.nih.gov/pubmed/26502280
Doets EL, In 't Veld PH, Szczecińska A, Dhonukshe-Rutten RA, Cavelaars AE, van 't Veer P, Brzozowska A, de Groot LC. Systematic review on daily vitamin B12 losses and bioavailability for deriving recommendations on vitamin B12 intake with the factorial approach. Ann Nutr Metab. 2013;62(4):311-22. doi: 10.1159/000346968. Epub 2013 Jun 20. http://www.ncbi.nlm.nih.gov/pubmed/23796635
Pramil N Singh, Joan Sabaté, and Gary E Fraser. Does low meat consumption increase life expectancy in humans? Am J Clin Nutr September 2003. Vol. 78 no. 3 526S-532S. http://ajcn.nutrition.org/content/78/3/526S.abstract