you'd be surprised... amazed... at how many guys with great physiques are absolutely clueless concerning nutrition, anabolics, and training (in general)
training is different.. they can usually do everything wrong and still look better than 19 out of 20 guys in the gym. but as far as training others? ha! they usually don't understand what's working for them or why, so how would they train others?
nutrition? same with training, they can eat shit and still look better than 19 out of 20 guys in the gym (if not 29 out of 30). at best they figure out the basics of what makes them look "good", but don't understand why. 90%.. fuck, 95% of the guys in any gym (i'd guess that 97% of the guys here) don't have a clue how many kcals' are in each gram of protein, carb, or fat... much less effects of different carbs (sucrose vs glucose vs fructose etc... or say, maybe how much water glucose will pull with it into cells in the form of glycogen).....
anabolics? hahaha... i've had clients who still just say "i need 5 tren" and have no idea it's actually called Trenbolone acetate lol.. been using the shit for 4,5,6 years and don't know what dianabol, anadrol, or testosterone proportionate are, but only know "dbol", "Drol", & "Test P", etc... have no clue how many actual mg's they're using of anything or total, they just know how many ml's of each they're supposed to inject or *drink each week or day.
*my orals are all liquid. i don't carry any tabs/cap's. generally
now, take 10 of those guys with genetics like the above, maybe 3 of them will actually want or care about competing. all they need is somebody to find out what they're eating(1), make a couple changes(2), observe how different things affect them(3), make conclusions and design their diet(finally, 4). far as nutrition goes, that's really all you need to do, so long as the person has a basic/advanced understanding of nutrition.
same goes with drugs, usually the same guy that does the nutrition... you're not really a "nutritionist", you're a "recovery-expert". since the drugs and food is used FOR recovery from training. helps if the same guy is a trainer, but not necessary. you can have one guy for each. the nutrition/drug guy is like the mechanic, and the trainer is like the race car driver.
the guys who do guys diets will usually do their drugs, like said above, because we have memory's like steel vaults and remember how each drug works just like how we remember how foods are supposed to work and how the body's process them.