I agree with you that we are all affected differently,
due to such things as weight, activity after eating,
and overall metabolism, which may include some
indeterminate factors.
There are a number of different systems for
trying to figure out these things.
One general guideline says,
One gram of carbohydrate raises the blood sugar about 3, 4, or 5 points for people who weigh 200 lbs., 150 lbs., and 100 lbs., respectively.
You would need to know how many grams of carbs you
are consuming.
There are also mathematical formulas for figuring out
how many units of insulin you need to lower your BG,
based on your total daily units. Even for that one,
there are two different formulas. You sort of have to
see which one works best for you.
For more info about carbs and figuring out amounts,
this website has just about all the items you will need.
Lotsa reading:
Carb Counting
