I guess you can start by asking them what they think their Idols eat and why and then go from there. It should be easier with athletes since nutrition is one of the cornerstones of physical fitness and every major athlete is on some sort of diet plat. You cant really build consistent muscle mass without proper nutrition so part of their commitment to their sport can be a commitment to better nutrition (assuming they are actually committed).

Shopping at whole foods is over rated, there is no nutritional difference between organic and not organic. One is fertilized with petroleum byproducts and the other one with human and other feces.

Since You are working with athletes, a diet plan should be part of the workout plan so you can explain it in those terms. Give them some basics and then have them come back to you in a couple days with their diet plan. Give them some diet goals like 35g protein a day, less than 10 of sugar, etc and them have them come back to you and show you how they tried to achieve that. Many will miss but they can tell you why, then you can figure out what problems they are having and work towards solutions.

Be careful of official government nutrition info it seems to be riddled with inadequacies and special interest lobbying (food pyramid). If you tailor your info to athletes and athletic nutrition you will be fine (although still tons of conflicting information).