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Cambridge University Science Magazine
Cysteine is a non-essential amino acid which we are able to intrinsically synthesise from dietary methionine.  A 2008 study showed a correlation between high cysteine levels and an increase (6-10kg) in fat mass. Within this positive correlation either factor could affect the other; however bariatric surgery for obese patients does not reduce cysteine indicating that this amino acid is causative of fat accumulation.

Moreover, it follows that any defects in cysteine metabolism would have an effect on body weight. Trisomy 21 (Down’s syndrome) supports this hypothesis, as a low resting metabolic rate may increase cysteine levels and explain the high level of obesity amongst these individuals. In homocystinuria, a defect in the production of enzymes involved in pathway of cysteine synthesis results in a low BMI and subcutaneous fat levels.

In contrast, a study of nine volunteers put on a high cysteine diet showed a 5% decrease in body fat. These conflicting results show no definitive evidence that cysteine causes weight gain, but point to common factors that affect both cysteine and a predisposition for obesity. Gamma-glutamyltransferase (GGT) for example is both an obesity marker and an enzyme that ultimately leads to cysteine release.

Cysteine-rich foods like asparagus aren’t recognisably linked to obesity; which together with the experimental data suggest that it may be sources of its precursor methionine in sources such as cow’s milk and nuts which is the link to excess fat.


Written by Zoe Chan.