High-animal protein and high-plant protein meals differentially alter postprandial plasma amino acid concentrations but not glucose homeostasis in people with overweight/obesity in a randomized, crossover, single-meal study.

BACKGROUND

In population studies, high-protein, particularly high-animal protein (HAP), intake is associated with an increased risk of developing type 2 diabetes. Results from preclinical studies suggest that this association might be mediated by branched-chain and other essential amino acids.

OBJECTIVES

This study aims to interrogate putative mechanisms linking high-protein intake and diabetes risk.

METHODS

We conducted a randomized, crossover, single-meal study in people with overweight/obesity to compare the effects of a standard (STD) meal (∼18 g protein/15% meal energy) and high-protein meals (∼28 g protein/22% meal energy) enriched with protein from either animal (n = 21) or plant (n = 21) sources on postprandial plasma amino acid, glucose, and key glucoregulatory hormone concentrations (180-min area under the curve).

RESULTS

Postprandial plasma amino acids were higher after the high-protein meals than the STD meal, with greater increases (all P < 0.05) after the HAP than the high-plant protein (HPP) meal in total essential (HAP compared with STD, 28% ± 3%; HPP compared with STD, 19% ± 3%; mean ± standard error of the mean) and total branched-chain (HAP compared with STD, 36% ± 3%; HPP compared with STD, 24% ± 3%), but not total (all) amino acids. Compared with the STD meal, both the HAP and HPP meals resulted in lower plasma glucose (HAP compared with STD, -4.3% ± 2.1%; HPP compared with STD, -5.2% ± 1.5%) and higher glucagon (HAP compared with STD, 48% ± 12%; HPP compared with STD, 44% ± 13%), glucagon-like peptide 1 (HAP compared with STD, 23% ± 6%; HPP compared with STD, 30% ± 12%), and insulin in relationship to glucose, without differences between the HAP and HPP meals.

CONCLUSIONS

Both the amount and type of protein are determinants of postprandial plasma amino acid concentrations, but only the amount, not the type of protein, is a determinant of plasma glucoregulatory hormone and glucose concentrations. Therefore, essential and branched-chain amino acids are not important regulators of postprandial glucose homeostasis. Nonprotein dietary or nondietary factors likely mediate the differential effects of HAP and HPP intake on glucose metabolism. This study was registered at clinicaltrials.gov as NCT03994367 and NCT05235464.