Animal-Protein Intake Is Associated with Insulin Resistance in Adventist Health Study 2 (AHS-2) Calibration Substudy Participants: A Cross-Sectional Analysis

High intakes of total and animal protein are associated with the risk of type 2 diabetes (T2D). The influence of protein type on insulin resistance, a key precursor of T2D, has not been extensively studied. The aim of this study was to determine the associations between dietary total, animal, and plant protein intakes as well as the animal-to-plant protein (AP) intake ratio with insulin resistance in middle-aged and older adults. This was a cross-sectional analysis in 548 participants (mean ± SD age: 66.2 ± 13.7 y) from the calibration substudy of the AHS-2 (Adventist Health Study 2) cohort. Participants consumed diets with a low AP intake ratio. Dietary intakes of total and particular types of protein were calculated from six 24-h dietary recalls. Participants completed a self-administered questionnaire on demographic, lifestyle, health, diet intake, and physical activity characteristics. Anthropometric variables including weight, height, and waist circumference were measured. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated by using fasting serum glucose and insulin. Multiple linear regression models were used to test the relations between total and specific protein intakes with insulin resistance. The ranges of dietary intakes of animal and plant protein and the AP intake ratio were 0.4-87.4 and 14.0-79.2 g/d and 0.02-4.43, respectively. Dietary intakes per 10-g/d increments of total protein (β: 0.11; 95% CI: 0.02, 0.21) and animal protein (β: 0.11; 95% CI: 0.01, 0.20) and the AP intake ratio (β: 1.82; 95% CI: 0.80, 2.84) were positively related to HOMA-IR. Plant protein was not significantly related to insulin resistance. Total and animal protein intakes and the AP intake ratio were positively associated with HOMA-IR in adults with relatively a low intake of animal protein and a high consumption of plant protein.