Abstract
Dietary and plasma total cysteine (tCys) have been associated with adiposity, possibly through interaction with stearoyl–CoA desaturase (SCD), which is an enzyme that is involved in fatty acid and energy metabolism. We evaluated the effect of a dietary intervention with low cysteine and methionine and high polyunsaturated fatty acids (PUFAs) on plasma and urinary sulfur amino acids and SCD activity indices. Fourteen normal-weight healthy subjects were randomized to a seven-day diet low in cysteine and methionine and high in PUFAs (Cys/Metlow + PUFA), or high in saturated fatty acids (SFA), cysteine, and methionine (Cys/Methigh + SFA). Compared with the Cys/Methigh + SFA group, plasma methionine and cystathionine decreased (p-values < 0.05), whereas cystine tended to increase (p = 0.06) in the Cys/Metlow + PUFA group. Plasma total cysteine (tCys) was not significantly different between the groups. Urinary cysteine and taurine decreased in the Cys/Metlow + PUFA group compared with the Cys/Methigh + SFA group (p-values < 0.05). Plasma SCD-activity indices were not different between the groups, but the change in cystine correlated with the SCD-16 index in the Cys/Metlow + PUFA group. A diet low in methionine and cysteine decreased plasma methionine and urinary cysteine and taurine. Plasma tCys was unchanged, suggesting that compensatory mechanisms are activated during methionine and cysteine restriction to maintain plasma tCys.
Highlights
There is increasing evidence on the importance of dietary protein in the regulation of metabolism and body adiposity, and a high habitual intake of predominantly animal protein is associated with increased adiposity in both cross-sectional and prospective studies [1,2,3,4,5,6,7]
Methionine and cystathionine decreased, whereas SAH and total homocysteine increased from baseline to day seven in the Cys/Metlow + polyunsaturated fatty acids (PUFAs) group compared to the Cys/Methigh + saturated fatty acids (SFA) group
We observed a significant group×time interaction for methionine, cysteine, and taurine, all of which were excreted to a lower extent in the Cys/Metlow + PUFA group compared to the Cys/Methigh + SFA group after seven days
Summary
There is increasing evidence on the importance of dietary protein in the regulation of metabolism and body adiposity, and a high habitual intake of predominantly animal protein is associated with increased adiposity in both cross-sectional and prospective studies [1,2,3,4,5,6,7] This is consistent with human studies observing that plant-based diets are associated with the prevention of weight gain, type 2 diabetes, and cardiovascular disease [6,8,9]. Methionine and cysteine are sulfur amino acids (SAAs) that are found in low amounts in plant foods and higher amounts in meats and fish [10]. Cysteine is readily oxidized to form a dimer containing a disulfide bond between two cysteine molecules, cystine, or with other thiols (including thiols in protein), thereby forming cysteine mixed disulfides
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