restriction of essential amino acids (eaas), restored fertility without reducing the longer lifespans that are typical of dietary restriction, leading the researchers to determine that methionine "acts in combination with one or more other eaas to shorten lifespan." restoring methionine to the diet of mice on a dietary restriction regimen blocks many acute benefits of dietary restriction, a process that may be mediated by increased production of hydrogen sulfide. methionine restriction can increase circulating liver hormone fgf21 between 5-fold and 10-fold in mice. several studies showed that methionine restriction also inhibits aging-related disease processes in mice and inhibits colon carcinogenesis in rats. in humans, methionine restriction through dietary modification could be achieved through a plant-based diet. restriction of dietary methionine reduces levels of its catabolite s-adenosylmethionine (sam-e), resulting is a subsequent loss of histone methylation. an active process mediated by a specific, preserved methylation of h3k9 preserves the memory of the original methylation profile, allowing the epigenome to be restored when dietary methionine levels return. a 2009 study on rats showed "methionine supplementation in the diet specifically increases mitochondrial ros production and mitochondrial dna oxidative damage in rat liver mitochondria offering a plausible mechanism for its hepatotoxicity". however, since methionine is an essential amino acid, it cannot be entirely removed from animals' diets without disease or death occurring over time. for example, rats fed a diet without methionine and choline developed steatohepatitis (fatty liver) and anemia, and lost two-thirds of their body weight over 5 weeks. administration of methionine ameliorated the pathological consequences of methionine deprivation. short-term removal of only methionine from the diet can reverse diet-induced obesity and promotes insulin sensitivity in mice, and methionine restriction also protects a mouse model of spontaneous, polygenic obesity and diabetes. health loss of methionine has been linked to senile greying of hair. its lack leads to a buildup of hydrogen peroxide in hair follicles, a reduction in tyrosinase effectiveness, and a gradual loss of hair color. methionine raises the intracellular concentration of glutathione, thereby promoting antioxidant mediated cell defense and redox regulation. it also protects cells against dopamine induced nigral cell loss by binding oxidative metabolites. methionine is an intermediate in the biosynthesis of cysteine, carnitine, taurine, lecithin, phosphatidylcholine, and other phospholipids. improper conversion of methionine can lead to atherosclerosis due to accumulation of homocysteine. other uses dl-methionine is sometimes given as a supplement to dogs; it helps reduce the chances of kidney stones in dogs. methionine is also known to increase the urinary excretion of quinidine by acidifying the urine. aminoglycoside antibiotics used to treat urinary tract infections work best in alkaline conditions, and urinary acidification from using methionine can reduce its effectiveness. if a dog is on a diet that acidifies the urine, methionine should not be used. methionine is allowed as a supplement to organic poultry feed under the us certified organic program. methionine can be used as a nontoxic pesticide option against giant swallowtail caterpillars, which are a serious pest to orange crops.