1) is anyone aware of additional studies published or in progress?
2) Is anyone doing this?
3) Whey and soy seem to have the least Met, btw
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2003 reference (www.pubmed.org, PMID: 12543260) to a feeding study with
calorically pair matched controls. The test diet (met 0.86% >> met 0.17%)
increased mean and maximal survival in Fischer rates by about **40%***.
Glutathione levels were also monitored. While the study implements
additional controls to address the questions of modest reductions in caloric
intake affecting the results, the study that (has this been done?) would be
useful would be 1) CR +/- met restricted diet, and 2) gene expression study
comparing CR to met restriction. Anyone know if these have been done?
Discussion snippet on Met restriction done with pair-fed rats:
"MR has repeatedly resulted in life span extension comparable to that seen
in energy restricted animals. In one of our typical studies using Fischer
344 rats, MR resulted in a 42% increase in mean survival and a 44% increase
in maximal longevity (Fig. 1). While living longer, animals on MR grow
significantly less (Fig. 2), and consume more food when food intake is
expressed on a per body mass basis. This latter observation has led to some
controversy, since when expressed on a per animal basis, MR rats, being
smaller, consume slightly less food per animal than their C-fed
counterparts. This has left open the possibility that the effect of
methionine restriction on life span is secondary to a restriction of caloric
intake, and not due to methionine deficiency. In order to examine the
proposition that MR might be an effect secondary to CR, we have pair-fed
rats, so that animals consumed control diet in the same quantity as consumed
by methionine restricted rats. Since animals fed in this way will consume
exactly the same energy levels regardless of which diet they consume, this
would exclude caloric intake as an explanation for the MR effect. When C
rats were fed in quantities equivalent to that consumed by MR animals they
consumed all of the food offered, and there was a modest reduction in weight
gain relative to ad libitum fed C animals. However, there was no
prolongation of life span (Fig. 3) associated with the slightly reduced food
intake and body size (Fig. 4), indicating that life span extension
associated with restricted methionine intake is not primarily due to reduced
energy consumption."
Discussion snippet on impact on [GSH] across body tissues...
"If GSH is, indeed, necessary to protect tissues against oxidative damage
during senescence, then feeding a diet that has neither cysteine nor
cystine, and only limited quantities of methionine, might be expected to
reduce survival since cysteine is the limiting amino acid in GSH synthesis
([Noda et al]). We have therefore measured blood GSH levels in aging Fischer
344 rats consuming either C or MR, and found that methionine restriction
brought about a 2-fold increase over controls despite the marked restriction
in sulfur-containing amino acid intake ( [Richie et al]). In most other
tissues MR was associated with maintenance of normal GSH levels throughout
senescence, the exceptions being liver (60% reduction) and kidney (25%
reduction). The unexpected maintenance of blood GSH levels in aged rats fed
a diet severely deficient in the rate limiting precursor cysteine probably
signals that there are important, and highly regulated, processes invoked by
MR."
