Frailty is a significant problem in aging societies. To monitor and prevent frailty, Japan introduced the Long-Term Care Insurance System and the Health Insurance System, which grant assistance to those with support/care needs. Certification for mild support/care needs mainly results from articular disease, fractures or falls, or aging-related weakness, all of which are associated with low muscle mass or physical activity levels. Protein is an important nutrient for preventing the loss of muscle mass and strength; studies suggest that high protein intake is associated with higher muscle mass and strength. However, in the Japanese Dietary Reference Intakes, which aim to prevent nutrient insufficiency and noncommunicable diseases, the recommended quantity and quality of protein for frailty prevention is unclear. Although the quantity and quality of protein intake in Japan improved significantly after World War II, studies suggest that Japan still suffers nutritional problems related to over- and undernutrition, including protein insufficiency and frailty.