From the Guidelines
Methionine is primarily excreted from the body through metabolism and excretion in urine, with its sulfur component ultimately being excreted as sulfate. This process involves the conversion of methionine to S-adenosylmethionine (SAM), then to homocysteine, and eventually to cysteine in the liver, as described in the study by 1. The body's regulation of methionine levels is crucial for protein synthesis and methylation reactions. Some key points to consider in methionine metabolism include:
- Methionine is converted to homocysteine, which can be further metabolized via the trans-sulfurylation pathway to produce cystathionine and cysteine, as noted in 1.
- The enzyme cystathionine b-synthase (CBS) plays a critical role in this pathway, requiring vitamin B6 as a co-factor.
- Excess methionine that isn't used for protein building or other metabolic functions is broken down, with nitrogen components converted to urea and excreted by the kidneys.
- Maintaining adequate hydration supports the normal excretion process of methionine and its metabolites. It's also important to consider that people with certain genetic disorders affecting methionine metabolism may need dietary restrictions or medical monitoring, as improper processing can lead to elevated methionine levels in the blood, as discussed in 1. Overall, understanding the metabolic pathways involved in methionine excretion is essential for appreciating the complex processes that regulate this essential amino acid in the body.
From the Research
Methionine Excretion
- Methionine is metabolized mainly by the liver, where it is converted to S-adenosylmethionine (SAMe) by the enzyme methionine adenosyltransferase 2
- The liver plays a crucial role in regulating SAMe homeostasis, and any fluctuations in SAMe levels can affect liver function 2
- Methionine restriction and supplementation have been shown to have various effects on the body, including extending lifespan and improving hepatic steatosis, but also potentially leading to adverse events such as hyperhomocysteinemia and bone-related disorders 3
- Methionine supplementation to a protein-free diet has been shown to reduce urinary nitrogen excretion by reducing the excretion of urea 4
- Methionine can regulate metabolic processes, the innate immune system, and digestive functioning in mammals, and also intervenes in lipid metabolism and the biosynthesis of glutathione to counteract oxidative stress 5
- Dietary sulfur-containing amino acids, including methionine, have been shown to affect calcium excretion, with high intake of methionine and cystine leading to increased urinary calcium and sulfate excretion 6
Excretion Pathways
- Methionine is excreted from the body through various pathways, including:
- Urinary excretion: Methionine is excreted in the urine, particularly in the form of urea 4
- Fecal excretion: Methionine is also excreted in the feces, although the exact mechanisms are not well understood
- Metabolic pathways: Methionine is metabolized into various compounds, including SAMe, homocysteine, and cysteine, which can then be excreted or used by the body for various functions 2, 5