BACKGROUND: With the aging phenomenon, there is growing interest in developing effective strategies to counteract dynapenia, the age-related loss of muscle strength. The positive effect of progressive resistance training on muscle strength is well known, however, the effect of nutritional supplementation or its synergistic effect along with exercise on muscle strength is not a consensus in the literature, especially in populations with low protein intake. METHODS: We analyzed the muscle strength (handgrip strength and sit-to-stand test), muscle mass, body mass index, insulin resistance, and physical function (gait speed, timed up & go test, and single-leg-stance test) of 69 dynapenic older adults with low protein intake, before and after the intervention period of three months. The participants were randomly allocated into four groups: resistance training, supplementation, resistance training plus supplementation, and control. RESULTS: There was a significant group x time interaction on the following outcome measures: handgrip strength (p <  0.001), gait speed (p =  0.023), and sit-to-stand test (p <  0.001). Considering the outcomes that showed a significant difference between and within groups, only the resistance training group and the resistance training plus supplementation group showed a large effect size in handgrip strength, gait speed, and sit-to-stand test, whereas the supplementation group showed a moderate effect size in gait speed. After the intervention period, there was no difference between the resistance training and the resistance training plus supplementation groups. CONCLUSION: This study reinforces the value of resistance training in improving muscle strength. The nutritional supplementation added no further benefits in this specific population. Registration number at the Brazilian registry of clinical trials: RBR-4HRQJF.