How the index is built
Blood sugar after a meal follows mostly how much sugar and starch you eat, and second, how fast it gets into your blood. The glycemic load puts both in one number: the food's glycemic index times the grams of carbs you digest in the serving, divided by 100.
The carbs for every meal come from the USDA's Nutritive Value of Foods, by item number, with the fiber taken out. The GI comes from the international tables (Atkinson 2008) or from the University of Sydney's GI database, with the study each value came from. When a dish was tested whole, like salmon sushi or chicken biryani, the index uses that number. Otherwise each carb food on the plate brings its own load, and the loads add up. Open "What it rests on" on any row to see the rows behind it.
Some foods have no GI test of their own, like a burger bun or a waffle. Those borrow the GI of the closest tested food and carry an "est." mark. Working out a meal from its parts tends to run high: in a study of 30 people, three meals with chicken, vegetables and sauce came out 22 to 50% lower when tested whole than the parts predicted. Meals with protein and fat probably make smaller hills than their load says.
The "in colas" column uses a 12 oz can of cola as the yardstick, a load of 22. People also differ a lot. In 800 people eating the same meals, the hills came out very different. The order is still a good guide to which meals push hardest, and a sensor worn for two weeks shows your own.