Dietary protein intake and kidney function decline after myocardial infarction: the Alpha Omega Cohort

Background: Post-myocardial infarction (MI) patients have a doubled rate of kidney function decline compared with the general population. We investigated the extent to which high intake of total, animal and plant protein are risk factors for accelerated kidney function decline in older stable post-MI patients. Methods: We analysed 2255 post-MI patients (aged 60-80 years, 80% men) of the Alpha Omega Cohort. Dietary data were collected with a biomarker-validated 203-item food frequency questionnaire. At baseline and 41 months, we estimated glomerular filtration rate based on the Chronic Kidney Disease Epidemiology Collaboration equations for serum cystatin C [estimated glomerular filtration rate (eGFR_cysC)] alone and both creatinine and cystatin C (eGFR_cr-cysC). Results: Mean [standard deviation (SD)] baseline eGFR_cysC and eGFR_cr-cysC were 82 (20) and 79 (19) mL/min/1.73 m². Of all patients, 16% were current smokers and 19% had diabetes. Mean (SD) total protein intake was 71 (19) g/day, of which two-thirds was animal and one-third plant protein. After multivariable adjustment, including age, sex, total energy intake, smoking, diabetes, systolic blood pressure, renin-angiotensin system blocking drugs and fat intake, each incremental total daily protein intake of 0.1 g/kg ideal body weight was associated with an additional annual eGFR_cysC decline of -0.12 (95% confidence interval -0.19 to -0.04) mL/min/1.73 m², and was similar for animal and plant protein. Patients with a daily total protein intake of ≥1.20 compared with <0.80 g/kg ideal body weight had a 2-fold faster annual eGFR_cysC decline of -1.60 versus -0.84 mL/min/1.73 m². Taking eGFR_cr-cysC as outcome showed similar results. Strong linear associations were confirmed by restricted cubic spline analyses. Conclusion: A higher protein intake was significantly associated with a more rapid kidney function decline in post-MI patients.