Dietary protein intake and grip strength in Japanese municipal workers

Grip strength is a simple and practical method for evaluating overall muscle strength and a key health biomarker that is linked to sarcopenia, chronic conditions and overall mortality. Although protein intake plays a vital role in muscle protein synthesis, its association with grip strength in adults remains unclear. This study examined the cross-sectional relationship between total, animal and plant protein intake and grip strength among local government workers in Japan. Participants were 349 workers (175 men and 174 women; mean age, 42·9 years; range, 19-71 years) who received a health check-up and participated in a nutrition and health survey. Protein intake was assessed using a validated self-administered diet history questionnaire. Grip strength was measured with a digital dynamometer. Multiple linear regression analysis was used to estimate adjusted means of grip strength according to the tertile of protein intake. Higher animal protein intake was significantly associated with higher grip strength in women, but not in men. After adjustment for covariates including lifestyle and dietary factors, mean (95 % CI) grip strength for the lowest through highest tertile of animal protein intake was 24·6 (21·7, 27·5) kg, 25·8 (22·9, 28·7) kg and 26·8 (23·7, 29·9) kg (P_{for trend} = 0·015) in women. No association was found between total and plant protein intake and grip strength in either men or women. These findings suggest that animal protein is important for muscle strength in women, with potential sex differences in the relationship between protein intake and grip strength.