The soy isoflavone genistein has been shown to alter key steps in muslce growth in the citro. To investigate its effect in vivo, 85 female rats were gred and randomly assinged to a basal corn-soy diet supplemented with graded level of genistein. The rats were given adlibitum access to the diet from day one of the gestration until parturition. Then all rats were provided the basal diet during lactation. Results indicated that dietary isoflavones reduced dam feed intake, but did not alter total pups born, average pup birth weight, pup growth rate, or average daily feed intake. Pup gain-to-feed intake was linearly increased and hind limb muscle weights and testicle weights were quadratically increased with increasing isoflavone intakes. These data indicate that feeding soy isoflavones to gravid rats decreased maternal feed intak and increased portnatal gain to feed ratios and the proportion of carcass musle.

Cook, D.R. and T.S. Stahly. 1998 Effects of dietary soy isoflavone concentrations in gravid rats on rate and efficiency of growth and muscle content of offspring. J.Animal Sci. (Suppl. 1)p163.