|Egg whites are among the best dietary sources of cysteine|
The news comes right from laboratories of London's King's and Imperial College, where McGavigan and colleagues investigated the effects of oral and intraperitoneal administration of a range of amino acids on food intake in rodents.
In their preliminary studies, McGavigan et al. identified l-cysteine, a conditionally essential amino acid that acts as a precursor for biologically active molecules such as hydrogen sulphide (H2S), glutathione and taurine, as an anorectic agent. Needless to say that they felt inclined to further investigated the effects of l-cysteine on appetite in rodents and humans and the mechanisms mediating these effects.
Where do you find cysteine in foods? Egg whites, whey protein (concentrate, Bounous. 1989) beef and milk are the best sources with 1.2g, 1.15g, 1.0g, and 0.72g per 200kcal serving. Cottonseeds, sprouted lentils, soy protein isolate and defatted sunflowers flour are top sources for vegetarians with 0.7g, 0.65g, 0.63g and 0.58g cysteine per 200kcal serving (nutritiondata.com).
This hypothesis is supported by the fact that l-cysteine didn't reduce the food intake of the gen. modified mice which overexpress ghrelin (data not shown in Figure 2).
The effects remain significant with repeated administration: Even when the "trick" is repeated thrice daily for five days, the administration of l-cysteine still lead to an acute reduction in food intake and a corresponding decrease in the cumulating food intake over the 5-day study period in rodents - in view of the short study period obviously without reductions in body weight.Now we all know that mice are no little men. Therefore, the important question that's rightly preying on your mind now is: Did this work in humans, as well? The answer is pretty straight forward: Yes, it did!
|Figure 3: 0.07g/kg l-cysteine in 200ml water lead to significant reductions in hunger ratings and acyl-ghrelin in humans as the corresponding dose in rodents (McGavigan. 2014)|
- Bounous, Gustavo, Gerald Batist, and Phil Gold. "Immunoenhancing property of dietary whey protein in mice: role of glutathione." Clin Invest Med 12.3 (1989): 154-61.
- Jordi, Josua, et al. "Specific amino acids inhibit food intake via the area postrema or vagal afferents." The Journal of physiology 591.22 (2013): 5611-5621.
- McGavigan, A. K., et al. "l-cysteine suppresses ghrelin and reduces appetite in rodents and humans." International Journal of Obesity (2014).