Effect of breakfast protein intake on muscle mass and strength in adults: a scoping review.

This scoping review examines the association between protein intake at breakfast and muscle mass and strength in adults. Analyzing 15 studies from various countries, primarily Japan, the review found that higher protein consumption at breakfast is generally associated with increased muscle mass in elderly, middle-aged, and young adults, though evidence regarding muscle strength improvements is less consistent. Some randomized controlled trials and observational studies reported positive effects on lean body mass and appendicular skeletal muscle index, while others found no significant changes in muscle strength or muscle protein synthesis. The review highlights the potential importance of breakfast protein intake for skeletal muscle health and calls for larger, high-quality randomized controlled trials to clarify its effects on muscle strength and to explore sex differences in these associations.