Elevated PGC‐1α in muscle dramatically protects against the sarcopenia, obesity, and diabetes that normally accompanies aging.42 Therefore, the use of l‐citrulline to increase PGC‐1α expression may be useful in the management of diseases such as obesity, diabetes, and sarcopenia, as well as in the enhancement of exercise performance. The gene discussed is PPARGC1A; the disease is diabetes mellitus.