Years ago food measurement was done by exchanges,
actually some still use it. However now counting carbs
seems to be the way to go.
http://www.diabetes.ca/files/Carb_Counting_eng.qx.pdf
The number of carbs in a meal does differ to some extent for
each individual. Depending mainly on a Person's size, gender
and an agreement between the Patient and the Dietician.
As you may have noticed in the Diabetic Menu Example that
I had posted earlier in "The Best Diet" thread by Javis (post
#2), the total carb count for each meal was 45 grams. That's
an average meal.