Whey protein is obtained from milk and is commonly marketed to enhance lean body mass of athletes who include resistance training in their workouts. As described in the entry for proteins, there is little research avaible to suggest that bodybuilders can synthesize more muscle from one protein than another. On the other hand, two studies have reported that casein may be used preferentially for body protein synthesis when compared to whey. In that research, the two proteins were fed to resting participants on separate occasions following an overnight fasting. Over a period of several hours, blood and breath collections revealed that whey protein was digested and absorbed more rapidly and was more likely to be metabolized for energy than casein and that casein was more likely to be used for protein synthesis. These studies did not demonstrate which proteins of the body were being synthesized nor did they address the issue of changes in body musculature during times of bodybuilding. The results do, however, pro¬ vide investigators with a potential reason to conduct such studies to determine if this effect could mean that casein is a better protein source for bodybuilders than whey. No other proteins have been similarly compared, which makes it impossible to assess the efficacy of other proteins (such as egg, soy, etc.) in comparison to whey or casein.