Are all sugars created equal?
Glycemic index is a way of measuring the impact a given amount of sugar/carbohydrate has on your blood sugar, diabetics absolutely need to know this (ask my Dad!) but this is something you definitely want to know as well if you’re trying to blast some belly fat. How potent is the foods sugar content?
Now, in order 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 Tescos to buy spices and there's a spice that's £500 a pound, that 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 till, 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. Still with me?
Glycemic load is a more sophisticated formula that takes into account the actual grams of carbs you're eating -- the standard portion size. The glycemic index for watermelon is high (GI 72), leading a lot of people to think you should never eat watermelon, which is a not really a thought through conclusion. Fact is, the average portion of watermelon has about 7 grams of carbs. You'd have to eat a few whole watermelons to have a significant impact on your blood sugar. Most of the weight is water after all... appropriately named fruit you might say!
The glycemic load of a watermelon, on the other hand, is only 5, making it an extremely low-glycemic food -- unless you're drinking pints or pure melon juice or eating 6 at a sitting. OR you give it to your 1 year old before bed, done that, learnt the lesson!! Portion size matters (as does sleep!). Don't actually try this by the way!!
White 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 sitting (including seconds, which is inevitable) and your blood sugar will be through 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 fibre, 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 at crazy intensity and a few times a day. Joe Blogs with Metabolic Syndrome... maybe not!