Methionine and cysteine are the most notable SCAAs (homocysteine and taurine also contain sulfur). Methionine is an essential amino acid, which must be obtained from dietary sources. Cysteine is conditionally essential, as it can be synthesized from methionine.

The SCAA-restricted group consumed approximately 19.2 mg of SCAA per kg of bodyweight per day (mg/kg/day), which is compliant with the U.S. Institute of Medicine’s recommended dietary allowance (RDA) of 19 mg/kg/day for combined methionine and cysteine intake (published in 2002).^[1]

Caloric intake was not measured directly in this study, although food diaries and questionnaires were used to assess adherence. Urinary sulfate excretion was lower in the SCAA-restricted group, indicating that SCAA intake was reduced in comparison with the control group.

Animal research has found that SCAA restriction extends the lifespans of rats, albeit at the expense of growth and development.^[2] Observational studies suggest that higher plasma cysteine levels are associated with higher risks of cardiovascular disease and diabetes.^[3] However, the restriction of SCAAs could increase muscle loss during energy restriction.^[4]

Sulfur-containing amino acid restriction for weight loss Original paper