I've had an advanced nutritionist for just a short time, of course. In the past 2 seasons, my entire team dropped a total of 1 stamina point, and that was a backup player. Since getting the nutritionist, my team has dropped another stamina point, and that was also a backup. Both my trainer and my nutritionist are 'advanced'. That's all I'm willing to spend for this, and whatever the results is next season, I will post the results. I will probably know the benefit by midseason, so will also post then.
BTW, to Lemonshine's post about tracking DMI, isn't it sports psychologist for GS and nutritionist for stamina? tracking nutritionists to measure GS would be incorrect? Maybe DMI measures both?