Sarcopenia is defined as an age-related loss of skeletal muscle mass and function and is recognized as a major clinical problem for older people. Essential amino acid supplementation, particularly β-hydroxy-β-methylbutyrate (HMB), a metabolite of leucine that is produced in skeletal muscle, has been evaluated in several studies as a nutritional approach to enhancing muscle protein synthesis in healthy or frail elderly subjects. Studies performed in in vitro conditions show that HMB may be effective in the treatment of muscle wasting, increasing myogenesis, reducing muscle apoptosis, and having a positive effect on muscle protein turnover; however, studies of the effects of HMB conducted in old animals have reported conflicting results. Clinical trials performed in older adults confirm that HMB can attenuate the progression of sarcopenia in elderly subjects. HMB supplementation results in an increase in skeletal muscle mass and strength in the elderly and its effect is even greater when combined with physical exercise. The role of HMB in sarcopenic obesity management is still under debate and a general lack of intervention studies in this population must be recognized. In conclusion, HMB appears to be effective for enhancing muscle mass and strength in the elderly. Less certain is the role of HMB supplementation in reducing fat mass and, thus, in the treatment of sarcopenic obesity.