Replacing dietary animal-source proteins with plant-source proteins changes dietary intake and status of vitamins and minerals in healthy adults: a 12-week randomized controlled trial

Abstract

Purpose: A shift towards more plant-based diets promotes both health and sustainability. However, controlled trials addressing the nutritional effects of replacing animal proteins with plant proteins are lacking. We examined the effects of partly replacing animal proteins with plant proteins on critical vitamin and mineral intake and statuses in healthy adults using a whole-diet approach.

Methods: Volunteers aged 20-69 years (107 female, 29 male) were randomly allocated into one of three 12-week intervention groups with different dietary protein compositions: ANIMAL: 70% animal-source protein/30% plant-source protein; 50/50: 50% animal/50% plant; PLANT: 30% animal/70% plant; all with designed protein intake of 17 E%. We analysed vitamin B-12, iodine, iron, folate, and zinc intakes from 4-day food records, haemoglobin, ferritin, transferrin receptor, folate, and holotranscobalamin II from fasting blood samples, and iodine from 24-h urine.

Results: At the end point, vitamin B-12 intake and status were lower in PLANT than in 50/50 or ANIMAL groups (P ≤ 0.007 for all). Vitamin B-12 intake was also lower in 50/50 than in ANIMAL (P < 0.001). Iodine intake and status were lower in both 50/50 and PLANT than in ANIMAL (P ≤ 0.002 for all). Iron and folate intakes were higher in PLANT than in ANIMAL (P < 0.001, P = 0.047), but no significant differences emerged in the respective biomarkers.

Conclusions: Partial replacement of animal protein foods with plant protein foods led to marked decreases in the intake and status of vitamin B-12 and iodine. No changes in iron status were seen. More attention needs to be paid to adequate micronutrient intakes when following flexitarian diets.

Clinical trial registry: NCT03206827; registration date: 2017-06-30.

Keywords: Animal-based foods; Flexitarian diet; Group B vitamins; Iodine status; Iron status; Plant-based foods.

Conflict of interest statement

LK was a board member of the company TwoDads at the time of the study. None of the other authors declare any conflicts of interest.

© 2021. The Author(s).

Figures

Fig. 1

Flow chart of participants. ANIMAL, a diet containing 70% animal and 30% plant source proteins; 50/50, a diet containing equal proportions (50:50) of animal and plant-based protein sources; PLANT, a diet containing 30% animal and 70% plant proteins

Fig. 2

Intakes of (A) vitamin B-12, (B) iodine (one iodine intake (732.8 µg) in the PLANT diet is not shown in the fig.), (C) iron mg, (D) plant-derived iron, (E) animal-derived iron, (F) folate, and (G) zinc of healthy adults (n = 136) who consumed intervention diets differing in animal and plant protein levels for 12 weeks. ANIMAL, a diet containing 70% animal and 30% plant proteins (n = 46); 50/50, a diet containing equal proportions (50:50) of animal and plant proteins (n = 46), PLANT, a diet containing 30% animal and 70% plant proteins (n = 44). *Differences between the diet groups analysed by ANOVA with Bonferroni correction: *P < 0.05, ** P < 0.01, ***P < 0.001. aOne observed vitamin B-12 intake (16.6 µg) in the 50/50 group is not shown in the fig

Fig. 3

Main sources in descending order of (A) vitamin B-12, (B) iodine, (C) iron, (D) folate, and (E) zinc in the intervention diets presented as average proportions among healthy adults (n = 136) who consumed intervention diets differing in animal and plant protein levels for 12 weeks at the end point of the intervention. Line colours: black = ANIMAL, a diet containing 70% animal and 30% plant proteins (n = 46), dark grey = 50:50, a diet containing equal proportions (50:50) of animal and plant proteins (n = 46), grey = PLANT, a diet containing 30% animal and 70% plant proteins (n = 44)

Fig. 4

Plasma, serum, whole blood, and urinary biomarkers. (A) serum holoTC, (B) U-I, (C) plasma ferritin, (D) plasma TfR, (E) blood haemoglobin, and (F) serum folate of healthy adults (n = 136) who consumed intervention diets differing in animal and plant protein levels for 12 weeks. ANIMAL, a diet containing 70% animal and 30% plant proteins (n = 46); 50/50, a diet containing equal proportions (50:50) of animal and plant proteins (n = 46); PLANT, a diet containing 30% animal and 70% plant proteins (n = 44). *A–B–B: Differences between the diet groups analysed by ANCOVA adjusted for baseline value with Bonferroni correction (A) or ANOVA with Bonferroni correction (B): * P < 0.05, ** P < 0.01, *** P < 0.001. C–E include female participants only. Fig. C: ANIMAL n = 36, 50/50 n = 36, and PLANT n = 34; D–E: ANIMAL n = 37, 50/50 n = 36, and PLANT n = 34. aTwo concentrations: 1006 µg/day from the ANIMAL diet and 618 µg/day from the PLANT diet