Protein source associated with risk of metabolic syndrome in adults with low and adequate protein intake: A prospective cohort study of middle-aged and older adults

Objectives: Metabolic syndrome is associated with an increased risk of diabetes, cardiovascular disease, and all-cause mortality. Some evidence suggests that the cardiometabolic health benefits of protein intake may vary by the source (animal or plant); however, the evidence is inconsistent. This study aimed to assess the risk of developing metabolic syndrome according to the protein source. Participants: Among a total of 3,310 participants aged 40 years or older in the Ansan and Ansung population based prospective cohort, 1,543 incident cases of metabolic syndrome were identified between 2007 and 2018. Measurements: Dietary intake was assessed using a validated food frequency questionnaire. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs) by quintile (Q), adjusting for demographics and health-related lifestyle factors. Results: Higher intake of animal protein (HR_{quintile5 (Q5) vs quintile1 (Q1)} [95% CIs]: 0.76 [0.59−0.96], P-trend ≤ 0.0307) and a higher relative intake of animal protein (HR_{Q5 vs.Q1}: 0.78 [0.64−0.95], P-trend ≤ 0.0017) were associated with a significantly decreased risk of developing metabolic syndrome. In subgroup analyses, associations between the risk of metabolic syndrome and the relative intake of animal and plant protein differed according to whether the total protein intake was within the recommended nutrient intake (RNI). Specifically, significant associations were observed only among those with a total protein consumption below the RNI (HR_{Q5vs Q1} [95% CIs]: 0.72 [0.56−0.93] for the relative intake of animal protein), but not among those consuming above the RNI. This association was more significant in women than in men. Conclusion: A higher absolute and relative intake of animal protein were associated with a significantly decreased risk of metabolic syndrome, particularly among those who consumed less than the RNI of protein.