After signing into their account from your gym's website, they will go to Nutrition >> Macro Log >> My Fitness Pal Settings>> Click Yes under Enable myfitnesspal.com food diary >> Click Check Your Settings on MFP >> Log in to MyFitnessPal (note it will take them directly to Food Diary Settings) >> Enable protein, carbs, fat and fiber for "Nutrients Tracked." >> Enter MyFitnesspal.com Username >> Click Save