Meeting Abstract
Dietary branched-chain amino acids (BCAAs) are commonly taken for muscle development. However, by stimulating growth via the Target of Rapamycin pathway, they may be detrimental to lifespan. We recently hypothesized that life-extension upon dietary restriction (DR) may result in part from increased oxidation of BCAAs, hence making them unavailable to overstimulate growth. Lubber grasshoppers (Romalea microptera) were chronically fed two levels of lettuce and BCAAs: ad libitum & BCAAs, ad libitum & buffer, DR & BCAAs, and DR & buffer. The BCAA solution contained the BCAA in the proportions found in lettuce. Lettuce dietary restriction decreased oviposition, but no difference in oviposition was seen upon BCAA force feeding. Dietary treatments were applied daily for at least 50 days (~1/3 of the lifespan) before sampling for hemolymph levels and oxidation rates, both in individuals. Hemolymph samples were collected >12h after any force feeding or lettuce feeding. In general, upon lettuce dietary restriction, BCAA force feeding slightly increased hemolymph BCAAs while buffer force feeding slightly decreased hemolymph BCAAs. The effect was significant for isoleucine (Pinteraction=0.042) and a trend for valine and leucine (P=0.105). There was no effect on hemolymph levels of BCAAs within the ad libitum-fed groups. Lettuce dietary restriction doubled the peak rate of oxidation of BCAAs (P<0.0001). In particular, peak oxidation rates were tripled for isoleucine (P<0.02), doubled for valine (P<0.04), and increased 50% for leucine (NS). Force feeding of BCAAs had little effect on oxidation of any BCAA. Based on these results, dietary restriction has two routes to reducing the availability of BCAAs (esp. isoleucine), which may reduce its availability to stimulate growth.
