Background & aims: Limited data are available on the relationship of protein from different food sources with metabolic syndrome (MetS) or changes in its components. We aimed to prospectively examine the relationships of protein intakes from animal, plant and major food groups with incident MetS and changes in its components.

Methods: 5324 participants from the Melbourne Collaborative Cohort Study, who were free of cardiovascular disease, cancer, hyperlipidaemia, elevated plasma glucose, elevated blood pressure and elevated waist circumference (WC) at baseline (1990-1994), were included in the present investigation. Dietary intake was assessed using a validated 121-item Food Frequency Questionnaire and MetS components were measured at baseline and follow-up (2003-2007).

Results: We documented 459 new cases of MetS during a mean of 11.2 years' follow-up. Multivariate-adjusted odds ratios (ORs) (95% CI) of incident MetS for the highest compared with lowest quartile of percentage energy intake from total, animal and plant protein were 1.46 (1.01-2.10), 1.67 (1.13-2.48) and 0.60 (0.37-0.97), respectively. Positive associations with incident MetS were seen for protein from chicken (OR (95% CI): 1.37 (1.00, 1.87)) and red meat (OR (95% CI): 1.47 (1.01, 2.15)), while inverse associations with incident MetS were observed for protein from grains (OR (95% CI): 0.62 (0.40, 0.97)), legumes and nuts (OR (95% CI): 0.74 (0.53, 1.04)). Each 5% increment in energy intake from animal protein was associated with a 0.97 cm (95% CI: 0.50, 1.45) increase in WC, a 0.97 mmHg (95% CI: 0.13, 1.82) increase in systolic blood pressure, and a 0.94 kg (95% CI: 0.57, 1.32) increase in weight over 11 years. However, an inverse association between plant protein and change in WC (-1.38 cm (95% CI: -2.68, -0.07)) and weight (-1.97 kg (95% CI: -3.00, -0.94)) was identified.

Conclusions: Our findings suggest that higher plant protein and lower animal protein consumption may help to prevent MetS.