On the CR list, Al Pater recently pointed to (1), an useful review on metabolic pathways modulated by -- and possibly involved in the anti-aging, life-extending effects of -- CR. One central focus of the paper is the mTOR pathway. There is now a great deal of converging evidence (as is dug into in much more detail in (2) (also available full-text thanks to Al)) that inhibiting mTOR plays a significant role in CR's anti-aging life extension effects -- most recently including the breakthrough report of robust life extension in mice using the rapamycin, an mTOR-inhibiting drug (3). This suggests that lowering leucine intake may enhance this mechanism of CR's effects.
Along with Calories and insulin signaling, a key regulator of mTOR is the branched-chain amino acid leucine, and there are now many reports (eg. (11-19)) that intake of either isolated leucine, or whey protein (which is unusually enriched in this and other BCAAs), enhances mTOR signaling relative to other aminos or proteins in rats and humans alike. This, in fact, is the basis for a lot of whey's popularity with bodybuilders: by activating mTOR, leucine (and to a lesser extent other branched-chain aminos) inhibits autophagic catabolism of muscle, leading to higher net muscle protein.
Of course, that same enhanced signaling inhibits the recycling of defective and damaged proteins, which is likely one of the core reasons that CR and other modes of mTOR inhibition retard aging.
Leucine is ubiquitous in protein, so one straightforward way to lower your leucine intake is to just cut your protein intake. Alternatively/additionally, because the amount of leucine per unit protein does vary quite a bit from food to food (whey protein being exceptionally high, as its vendors will enthusiastically remind you), you can look for foods low in leucine per unit protein with Nutritiondata.com's nutrient search tool.
A couple of gems from my own digging for relatively protein-rich foods low in leucine AND methionine: lentils and fava beans. A simple and tasty-sounding recipe I found for the latter:
Fool Medames (Egyptian Beans)
1 lb Dried sm. fava or pink beans
Lightly salted water
1/2 c Red lentils
3 tb Lemon juice
1/4 c Olive oil
1/2 ts Cumin, ground
Salt and pepper to taste
1/2 c Green onions, chopped
Sort and rinse dried beans. Place in a large saucepan and add lightly salted water to cover. Bring to a boil. Reduce heat and cover. Simmer over low heat 2 1/2 hours. If necessary, add more water to keep beans covered. Add lentils and cover. Simmer 30 minutes longer or until lentils and beans are tender and mixture is thick but not soupy. Stir in lemon juice, olive oil, cumin, salt and freshly ground pepper. Serve hot, sprinkling each serving with a portion of green onions.
The same site has many other fava bean recipes, and indeed recipes for a variety of legumes.
FWIW, replacing casein with lactalbumin (~70% of the protein in whey) in AL diets doesn't seem to affect longevity in F344 rats, whereas using soy is clearly better for them (4,5); however, this may not mean much, as F344s are somewhat weird animals to work with because of their high vulnerability to nephropathy, which soy protein significantly alleviates. Lactalbumin has inconsistent (depending especially on gender) but generally favorable effects compared with commercial diets in hamsters (6,7); and it was reported to extend longevity when substituted for casein late in life in mice (8), possibly due to the presence of precursors of glutathione, during the time when age-related oxidative stress has begun to set in and recycling of GSH becomes impaired.
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