Sulfur amino acids, metabolic health and beyond: Recent advances, translational implications, and future research considerations

Dietary restriction of the sulfur amino acids methionine and cysteine (sulfur amino acid restriction [SAAR]) is a well-established paradigm for delaying disease onset and the aging process in several experimental models. In vivo, SAAR's anti-aging effects appear to be mediated by decreased growth hormone/insulin-like growth factor-1 (GH/IGF-1) signaling, along with improvement in insulin sensitivity and overall metabolic health. SAAR-fed animals also exhibit reduced regional and total adiposity, as well as oxidative stress and inflammation. Recent experimental studies suggest that SAAR improves cognition, induces significant changes in gut microbiome composition, and that its benefits may depend on the age at which the intervention begins. In humans, observational studies have shown that higher plasma total cysteine levels are positively correlated with adiposity, insulin resistance, and an increased incidence of diabetes. Likewise, high dietary methionine and cysteine intake has been linked to increased risk of cardiovascular disease and diabetes-related mortality. Human dietary intervention studies have only been partly successful in translating the benefits of SAAR, and practical challenges for implementation remain to be addressed. This review summarizes recent advances in the SAAR field and discusses its translational potential for promoting metabolic health and reducing the risk of age-related diseases.