GI is a measure of how quickly a carbohydrate laden food is converted into glucose and enters the blood stream. The value is assigned relative to glucose which the body uses as fuel. To compare GI value of different foods, you take foods containing an identical amount of digestible carbohydrates and compare how quickly those are broken into glucose which hits the blood stream. 600 grams fo spinach (GI=15) contains as much carbohydrate as 100 gram of rice (GI=72). This makes them hard to compare on a practical basis.
Glycemic Load was supposed to help with this issue. Glycemic Load is derived from the Glycemic Index. You multiply the GI times the available carbohydrate in the food and divide it by 100 to arrive at a GL value. So a high GI food can have a low glycemic load value. Spinach has a close to zero value per cup whereas for the same measure of rice has a value of 15.
All carbohydrates need to be broken down into glucose to be used by the body. Insulin is a hormone which aids in getting glucose into different parts of the body for use as energy. Using the goldilocks analogy again, we don’t want the glucose to enter too quickly or too slowly. GI or GL could be useful in picking individual foods since the GI/GL value could be a guide to how quickly the food is converted to energy. But it can be near impossible to get a read on the GI or GL of your meal if you are eating a variety of fruits, vegetables, protein, dairy, pulses, nuts and starch in a meal. The GI of the starch-rich food is impacted by all the other foods you consume alongside it.
So white rice is a high GI food. But what happens if you pair 1/2 cup of rice with 1 cup of dal, 1 /2 cup of yoghurt and 1.5 cups of vegetables. The rate at which the rice becomes glucose is much slower. What happens if 3-5 cups of white rice is paired with 1/2 cup of curd, 1/2 cup of vegetables and 1/2 cup fo dal.
You are consuming far too much rice and that energy is extremely unlikely to have any use for the body. The rice will be broken down into glucose quicker than the first meal too. You didn’t need to know the GI or GL of that meal to figure that though did you?