Although sarcopenia has been dealt with in several studies, the standardized guidelines for preventing sarcopenia resulting from increased life expectancy are still insufficient. Therefore, this study evaluated the effects of daily resistance exercise and the intake of leucine-rich protein supplements daily for 12 weeks on the body composition and physical function of healthy adults aged >50 years living in Korea. The study analyzed 50 healthy people without medical conditions, who were randomly assigned to two groups (taking either protein powder or placebo powder) twice a day for 12 weeks. All participants performed resistance exercises regularly that could be repeated 8–12 times using a TheraBand for 12 weeks. A total of 41 participants completed the study. When measured via bioimpedance analysis (BIA), body fat mass (kg) and body fat (%) significantly decreased, and lean body mass (LBM) (kg) and skeletal muscle mass (SMM) (kg) significantly increased, in both groups. However, when measured via dual-energy X-ray absorptiometry (DXA), LBM was significantly increased only in the protein powder group. The LBM and SMM change measured via BIA was significantly greater in the protein powder group than in the placebo powder group (LBM: 0.95 ± 0.91 kg in the protein powder group vs. 0.38 ± 1.06 kg in the placebo powder group, p = 0.043; SMM: 0.69 ± 0.58 kg in the protein powder group vs. 0.29 ± 0.65 kg in the placebo powder group, p = 0.039, respectively). In the senior fitness test (SFT), significant functional improvement was found within the two groups, but no significant difference was found between the groups in the degree of improvement. In conclusion, in older people aged >50, to prevent sarcopenia, is more effective to combine resistance exercise and leucine-rich protein supplementation than to simply perform resistance exercise.