Increased consumption of plant-based foods and decreased consumption of animal-based foods is recommended for healthy diets and sustainable food production. We investigated the effects of partial replacement of dietary animal proteins with plant-based ones on intake of energy-yielding nutrients, fibre, and plasma lipoproteins. This 12-week randomised clinical intervention comprised 107 women and 29 men (20–69 years) in three diet groups with different dietary protein compositions (“ANIMAL”: Animal 70%/plant 30%; “50/50”: Animal 50%/plant 50%; “PLANT”: Animal 30%/plant 70%; all: Protein intake 17 E%). Nutrient intakes were assessed by 4-day food records. Saturated fat intake (E%) was lower and polyunsaturated fatty acid intake (E%) higher in the PLANT and 50/50 groups compared to the ANIMAL group (p < 0.001 for all). Fibre intake was higher in the PLANT (p ˂ 0.001) and 50/50 (p = 0.012) groups. Total and LDL cholesterol were lower in the PLANT than in the ANIMAL group (p = 0.003 for both) but no differences in HDL cholesterol or triglycerides were observed (p > 0.05). Replacing animal protein with plant protein sources in the diet led to an increased fibre intake and improved dietary fat quality as well as blood lipoprotein profile. Flexitarian diets could provide healthy and more sustainable alternatives for the current, predominantly animal-based diets.

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.

Plant-based diets may reduce the risk of chronic diseases, but can also lead to low calcium and vitamin D intakes, posing a risk for bone health. We investigated whether partial replacement of animal proteins with plant-based proteins using a whole-diet approach affects bone and mineral metabolism in healthy adults in 3 groups fed diets differing in protein composition. This 12-week clinical trial was comprised of 107 women and 29 men (20-69 years old; BMI mean ± SD, 24.8 ± 3.9) randomly assigned to consume 1 of 3 diets designed to provide 17 energy percent (E%) protein: "animal" (70% animal protein, 30% plant protein of total protein intake), "50/50" (50% animal, 50% plant), and "plant" (30% animal, 70% plant) diets. We examined differences in bone formation [serum intact procollagen type I amino-terminal propeptide (S-iPINP)], bone resorption [serum collagen type 1 cross-linked C-terminal telopeptide (S-CTX)], mineral metabolism markers (primary outcomes), and nutrient intakes (secondary outcomes) by ANOVA/ANCOVA. S-CTX was significantly higher in the plant group (mean ± SEM, 0.44 ± 0.02 ng/mL) than in the other groups (P values < 0.001 for both), and differed also between the animal (mean ± SEM, 0.29 ± 0.02 ng/mL) and 50/50 groups (mean ± SEM, 0.34 ± 0.02 ng/mL; P = 0.018). S-iPINP was significantly higher in the plant group (mean ± SEM, 63.9 ± 1.91 ng/mL) than in the animal group (mean ± SEM, 55.0 ± 1.82 ng/mL; P = 0.006). In a subgroup without a history of vitamin D supplement use, plasma parathyroid hormone was significantly higher in the plant than in the animal group (P = 0.018). Vitamin D and calcium intakes were below recommended levels in the plant group (mean ± SEM, 6.2 ± 3.7 μg/d and 733 ± 164 mg/d, respectively). Partial replacement of animal proteins with plant-based proteins for 12 weeks increased the markers of bone resorption and formation among healthy adults, indicating a possible risk for bone health. This is probably caused by lower vitamin D and calcium intakes from diets containing more plant-based proteins, but it is unclear whether differences in protein intake or quality play a major role. This trial was registered at clinicaltrials.gov as NCT03206827.

Purpose: A transition to more plant-rich diets is an effective way to reduce the climate impact of a diet. Using a whole-diet approach, we studied how partial replacement of animal-sourced with plant-sourced proteins affected the dietary climate impact while simultaneously considering diet-related health biomarkers. Methods: In a 12-week randomised controlled trial, 107 women and 29 men were assigned into three diet groups (ANIMAL, 50/50, PLANT) with animal-to-plant-protein ratios of 70/30, 50/50, and 30/70, respectively. Life-cycle-assessment-based coefficients for foods were used to assess the climate impact of the diet groups, based on four-day food records. Correlations between climate impact and biomarkers were assessed. Results: The climate impact (CO₂ eq.) for PLANT was 3.32 kg per day, 3.05 kg per 2,000 kcal, and 0.04 kg per gram of protein, for 50/50 4.34, 4.20, and 0.05 kg, and for ANIMAL 4.93, 4.94, and 0.06 kg, respectively (p < 0.05 for all except ANIMAL vs. 50/50 /g protein and /2,000 kcal). Climate impact correlated weakly positively with colorectal cancer risk markers and a positive status of bone turnover, but not with cardiometabolic risk markers. Animal-based iron intake and climate impact (per 2,000 kcal) had a strong positive correlation 0.70 C.I. [0.60, 0.77], while saturated fat (0.29 [0.13, 0.44]) and calcium (0.37, [0.22, 0.51]) intake had a weak positive correlation, and fibre intake (− 0.37, [− 0.51, − 0.21]) a weak negative correlation with climate impact. Conclusion: Replacing animal-sourced proteins with plant-sourced proteins reduced the climate impact of the diet. The relationship between climate impact and biomarkers was more ambiguous indicated by both beneficial and harmful indicators within lower climate impacts. Clinical trial registry: NCT03206827; registration date: 2017–06–30.

Purpose: Legumes are recommended as a sustainable alternative protein source to red and processed meat (RPM). We studied the effects of a partial substitution of RPM with non-soy legumes on nutrient intakes and status, anthropometric measurements, and biomarkers of cardiovascular diseases and type 2 diabetes risk in healthy working-age men. Methods: In a 6-week clinical trial, 102 men (mean age 38 years, range 21–61) were randomized to either the MEAT group, consuming 760 g/week of RPM (25% of total protein intake (TPI)) or the LEGUME group, consuming 200 g/week of RPM corresponding to the maximum of the Planetary Health Diet (5% of TPI) along with legume-based foods containing protein equivalent to 560 g/week of red meat (20% of TPI). TPI target was 18 E%. Four-day food records, blood, and 24-h urine samples were collected at baseline and endpoint. Results: At the endpoint, the LEGUME group had higher intakes of fiber (g/MJ, P = 0.006), polyunsaturated fatty acids (E%, P < 0.001), and iron (mg/MJ, P < 0.001) compared to the MEAT group, but lower intakes of saturated fatty acids (E%, P = 0.012) and vitamin B12 (µg/MJ, P < 0.001). The LEGUME group had lower vitamin B12 status (holotranscobalamin, P = 0.022), iodine status (24-h urinary iodine excretion, P = 0.041), total and LDL cholesterol (both P < 0.001), and BMI and weight (both P = 0.009). Conclusion: Implementing a moderate dietary shift by consuming more legumes and less RPM may beneficially affect biomarkers of cardiovascular diseases and weight in healthy working-age men while maintaining nutritional adequacy of iodine, iron, and vitamin B12 in the short term. Trial Registration Clinical trial registration ClinicalTrials.gov as NCT04599920 in October 2020.

The transition towards more plant-based diets may pose risks for bone health such as low vitamin D and Ca intakes. Findings for the contribution of animal and plant proteins and their amino acids (AA) to bone health are contradictory. This 6-week clinical trial aimed to investigate whether partial replacement of red and processed meat (RPM) with non-soya legumes affects AA intakes and bone turnover and mineral metabolism in 102 healthy 20–65-year-old men. Participants were randomly assigned to diet groups controlled for RPM and legume intake (designed total protein intake (TPI) 18 E%): the meat group consumed 760 g RPM per week (25 % TPI) and the legume group consumed non-soya legume-based products (20 % TPI) and 200 g RPM per week, the upper limit of the Planetary Health Diet (5 % TPI). No differences in bone (bone-specific alkaline phosphatase; tartrate-resistant acid phosphatase 5b) or mineral metabolism (25-hydroxyvitamin D; parathyroid hormone; fibroblast growth factor 23; phosphate and Ca) markers or Ca and vitamin D intakes were observed between the groups (P > 0·05). Methionine and histidine intakes were higher in the meat group (P ≤ 0·042), whereas the legume group had higher intakes of arginine, asparagine and phenylalanine (P ≤ 0·013). Mean essential AA intakes in both groups met the requirements. Increasing the proportion of non-soya legumes by reducing the amount of RPM in the diet for 6 weeks did not compromise bone turnover and provided on average adequate amounts of AA in healthy men, indicating that this ecologically sustainable dietary change is safe and relatively easy to implement.