A Catch 22: the Role of Dietary Methionine

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Methionine is the only essential amino acid that contains sulfur.  (Cysteine also contains sulfur but is semi-essential because it can be synthesized from serine and methionine.)  The ratio of methionine to glycine within your body is crucial since glycine acts primarily as an antioxidant (it is converted to glutathione), whereas methionine generally has an oxidizing effect.  A number of scientific studies have observed methionine-restriction diets to confer life-extending effects upon various animals including rats, mice, and fruit flies.  Given the abundant variability in studies of methionine restriction diets, however, we decided to summarize some of the relevant scientific literature to see if there are any general discernable patterns that may be applicable to humans.

Key Research Findings:

• Studies conducted so far indicate rats, mice, and fruit flies have benefited from a low-methione diet.  An almost-zero-methionine diet causes disease and ultimately death; (complete removal of methionine is almost impossible, as it is an integral component in nearly all proteins).  It has been observed, however that reducing dietary methionine intake by half of "normal" levels confers significant anti-aging benefits via reduction in the generation of reactive oxygen species (ROS) in rats.  2008.  

• A well-written review article of caloric-restriction (CR) diets found that methionine appears to be a key culprit in aging; restriction of fat, carbohydrates or any other isolated amino acids apparently has no effect on lifespan of both humans and animals studied in laboratory settings.  2011.

• Interestingly, many cancers rely upon gross intakes of methionine because their regeneration pathways are mutated; they also need to synthesize lots of new proteins for cellular growth.  2011.  Note this is an important paper for cancer treatment because it clearly demonstrates that diet can influence cancer growth.  While this is not surprising for us, many oncologists (and other doctors) don't quite recognize the importance of diet in relation to disease... yet.

• It's further interesting to note cancerous tumors create a sulfurous stench that appears to help them grow and mutate.  The sulfurous compounds are creating by reacting excess glucose with methionine; knowing such may provide us with good reason to limit dietary intake of both compounds.  2012.

• Apparently the "bad boy" status of methioinine is attributable to its generation of ROS in mitochondria...but as always, there's a catch: some ROS generation appears to be a good thing!  2014.

The information presented above provides ample evidence indicating methionine intake beyond that which is required for daily cellular function can possibly instigate or worsen diseases such as cancer in humans.  However it's important to remember that nutrition science is an ongoing process; with all we think we do know, there's at least ten times as much that we don't.  (For example, another study conducted in 2011 observed dietary glycine supplementation confers the same health benefits as those associated with methionine restriction in laboratory rats.)  It's clear our understanding of physiological processes at the cellular level is continually developing.  However the above information may be beneficial to you in developing a diet that energizes you, and helps you live a long and content life.

For additional reading on this subject, and others, refer to Do High-Protein Diets Cause Kidney Disease and Cancer? by Chris Kresser and 5 Reasons Why Even Vegetarians Should Eat Gelatin by Laura Schoenfeld.