While methionine restriction brings similar longevity and health benefits to calorie restriction where it has been tested, it doesn't appear to be quite the same thing under the hood - probably meaning the calorie restriction operates through additional mechanisms beyond a reduction in methionine intake: "Life span can be extended in rodents by restricting food availability (caloric restriction [CR]) or by providing food low in methionine (Meth-R). Here, we show that a period of food restriction limited to the first 20 days of life, via a 50% enlargement of litter size, shows extended median and maximal life span relative to mice from normal sized litters and that a Meth-R diet initiated at 12 months of age also significantly increases longevity. Furthermore, mice exposed to a CR diet show changes in liver [biochemistry, including gene expression patterns] that are not observed in liver from age-matched Meth-R mice. These results [suggest] that the spectrum of metabolic changes induced by low-calorie and low-methionine diets may differ in instructive ways." This is also a helpful reminder that starting calorie restriction later in life isn't a waste, and can still provide significant health benefits.

Link: http://biomedgerontology.oxfordjournals.org/cgi/content/full/glp051