I don't know how to calculate it. But I do know that the combination matters. Try this experiment. Eat a bagel plain for breakfast. Wait as long as you can for lunch. Note when you start feeling like you are starving and your hands get shaky (blood sugar crash). Next day eat the bagel with peanut butter. Note how you feel after the same amount of time. I predict the blood sugar crash will later, or won't happen at all.

I have found that the secret to sustaining a vegan diet is beans (resistant starch). They release sugar into your blood over many hours, blunting the blood sugar roller coaster that would otherwise be caused by eating a lot of fruits and vegetables without a lot of meats and fat.

I have done a version of the above proposed experiment with a foot long Subway sandwich, veggies only (no meat, no cheese, no mayo). I feel like I am starving in 3 hours. Add hummus, I feel fine for 6 hours. I know it adds some calories, but I'm convinced it is more about the resistant starch. According to this video https://nutritionfacts.org/video/beans-and-the-second-meal-e... eating beans in one meal even reduces the blood sugar spike in later meals!

Another interesting thing. There is a Ted Talk about how glycemic response varies by individual due to different makeup of gut bacteria. I think it is this one: https://www.youtube.com/watch?v=0z03xkwFbw4. The guy claims he can analyze your gut bacteria and tell you which foods will spike your blood sugar. Subway might be bad for me but fine for you!