Summary: In a 10-week trial in adults with metabolic syndrome, both a mostly plant-protein and a mostly animal-protein calorie-restricted diet improved weight, blood pressure, and atherogenic index, but there were no significant differences between the two diets except for the metabolic hormone adropin.
PICO Summary
| Element | Detail |
|---|---|
| Population | 73 adults with metabolic syndrome (mean age ~44); parallel, randomised, slightly calorie-restricted trial over 10 weeks, Iran. |
| Intervention | Diet with 70% plant-based and 30% animal-based protein. |
| Comparison | Diet with 70% animal-based and 30% plant-based protein. |
| Outcome | Within both groups, weight, BMI, blood pressure, and atherogenic index of plasma fell and adropin rose (p<0.05). Waist circumference and triglycerides fell only in the plant group, and HDL rose only in the animal group. Between-group analyses showed no significant differences in crude or adjusted models, except for a difference in adropin in the per-protocol analysis. |
Expert Commentary
This trial must be read with the between-group comparison in front, because that is what tests the question of protein source, and on that measure the result is essentially null: both diets improved metabolic-syndrome components similarly, with no significant separation apart from a per-protocol difference in the novel hormone adropin. The honest interpretation is that, over ten weeks, the calorie restriction shared by both arms did the heavy lifting, and protein source mattered little for the main outcomes. The within-group contrasts, plant protein lowering waist and triglycerides and animal protein raising HDL, are hypothesis-generating at best and should not be presented as proof of differential benefit, since they were not significant between groups. Limitations reinforce caution: a short duration, modest sample, unspecified protein sources, self-reported adherence, and a single centre. Can I use this with my patients? Yes, with a balanced message. I would tell patients that achieving an energy deficit is what most improves metabolic syndrome, that both plant- and animal-protein patterns can work, and that shifting toward whole-food plant proteins is reasonable for broader cardiovascular reasons drawn from larger evidence, while being clear this particular trial did not show one protein source beating the other.
References
Shahdadian F, Rezazadegan M, Rouhani P, et al. Does partial replacement of animal protein with plant protein in the diet affect components of metabolic syndrome, adropin levels, and the atherogenic index of plasma? Results from a parallel randomized clinical trial in adults with metabolic syndrome. Nutr Diabetes. 2025;15(1):43. doi:10.1038/s41387-025-00401-x