But is that contract binding? If he is engaging in illegal activity, maybe it's not. Of course, bodybuilders won't want to take it to court because they will also be implicated for engaging in the activity.
Good question. I'm not a lawyer, but my guess is that the contract would specify that he was being hired strictly as a nutritional adviser, and that the athletes are agreeing to only accept advice on diet and perhaps use of otc supplements.
I suppose he'd probably have something in there about the athletes consenting that they are in good health to their knowledge. The contract could possibly state that he and they are acknowledging that they are not engaging in any illegal or potentially dangerous activities, and that they have the choice to follow his advice or not.
Perhaps this would absolve him from any accountability if the athletes were given any off-the-record verbal "suggestions" that may not be legal and / or safe. But this is all just speculation on my part. Are there any lawyers reading this board?