Glycemic load/ glycemic index

Glycemic index is a way of measuring the impact a given amount of carbohydrate has on your blood sugar, something you definitely want to know. But to do a fair comparison, they have to use a fixed amount. In the case of the glycemic index, it's a standard 50 grams of carbohydrate.
Problem is, very few carbohydrate foods in real life are 50-gram portions.
See, if you go to a store to buy spices and there's a spice that's $500 a pound, that sure sounds like a lot of money. But if you're only buying a half-teaspoon of the stuff, it's pretty irrelevant. You want to know what you're going to pay at the register, not necessarily what you'd pay if you bought a pound.
Similarly, you really don't care what the impact of 50 grams is on your blood sugar; you care what the impact of the amount you're actually eating is.
Glycemic load is a more sophisticated formula that takes into account the actual grams of carbs you're eating -- the portion size. The glycemic index of carrots is high, leading a lot of people to think you should never eat carrots, which is a dumb conclusion. Fact is, the average carrot has 3 grams of carbs. You'd have to eat like a giant rabbit to have a significant impact on your blood sugar.
The glycemic load of a carrot, on the other hand, is only 3, making it an extremely low-glycemic food -- unless you're drinking pure carrot juice or eating 13 carrots at a sitting.
Pasta, on the other hand, has a moderate glycemic index, but is almost never eaten in 50-gram portions. Factor in the portion size at a typical Olive Garden and your blood sugar will be on the roof, and stay there for a week. Not surprisingly, the glycemic load of pasta is very high.
The technical formula for glycemic load is GI (glycemic index), multiplied by the number of grams of carbohydrates in the portion, then divided by 100. Low glycemic load is between 1 and 10, medium is between 10 and 20, and anything over 20 is very high.
That said, remember that both glycemic index and glycemic load only refer to the food eaten alone. Add some fat or protein and the total impact goes down. And plenty of high-glycemic foods are good for you (say, carrot juice) while plenty of low-glycemic foods (fried donut holes) are not.
So take glycemic load into account, but don't be a slave to it. It's just one measurement to consider when planning a diet.
Incidentally, athletes in training actually can benefit from high-glycemic foods, especially when they're training twice a day. Mrs. Smith with Metabolic Syndrome... not so much!