Analyzing dietary exposure to critical nutrients on a plant-based diet using the food- and total nutrient index

Unfortified plant-based diets are devoid of vitamin B12, and supply low intakes of iodine, zinc, selenium, and calcium. To disentangle the complex interplay between nutritional adequacy and nutrient intakes from supplements and foods in plant-based diets, data from a Germany-based cross-sectional study examining the nutritional status of omnivores, lacto-ovo-vegetarians and vegans was re-analyzed. Special emphasis was put on potentially under-consumed nutrients in plant-based diets, including vitamin A and choline.

A novel tool focusing on under-consumed micronutrients was employed to shed a new light on nutrient supply and dietary exposure to critical nutrients in plant-based diets: The Total Nutrient Index (TNI). The TNI extends existing measures of diet quality by considering nutrient intake data from both foods and supplements. The TNI covers calcium, magnesium, potassium, choline and vitamins A, C, D, and E. The TNI was compared between omnivores, vegetarians and vegans, with a special focus on its micronutrient component scores and with regard to dietary supplement contributions.

Data from 108 participants was analyzed. The vegan and the omnivorous diet resulted in similar TNI scores (73.70 ± 19.68 and 72.77 ± 17.88), whereas lacto-ovo-vegetarians scored lower (68.50 ± 17.10). The contribution of supplements to the TNI was higher in vegans and omnivores (median contribution: 12.50 (16.80) and 10.81 (18.23) score points, respectively) as compared to lacto-ovo-vegetarians (3.42 (12.50) score points). High micronutrient component score contributions to the TNI were found for vitamin D supplements (all dietary groups), vitamin C supplements (omnivores and vegans) and magnesium supplements (all groups).

Supplementation has a profound impact on nutrient supplies in individuals on a plant-based diet. This study reiterates the need to quantitatively assess nutrient intakes from supplements to assess diet quality of plant-based dietary patterns. We posit that defining diet-specific TNI scores is important for a precise evaluation of diet quality, whether in omnivore or in the spectrum of plant-based diets.