"The Zone diet is not about the glycaemic index of carbohydrates, but the insulin
index"
- Barry Sears, Zone Perfect Meals in Minutes
The concept of the glycaemic index of foods is becoming quite well known. It is often mentioned in the media, the diet The G.I. Factor is based on it, and now the index of some foods are shown on their labels. But what's not widely understood is the reason why the glycaemic index is important to our health. If people knew this they would realise that it is futile to consider the glycaemic index of a meal whilst ignoring its glycaemic load, because both affect our insulin levels. What we should be thinking about is the insulin index of our meals.
The glycaemic index is a rating given to individual foods (that contain carbohydrates) according to how fast they cause blood sugar to rise after they're eaten. Three main factors influence the glycaemic index of a particular food:
Fibre has the greatest negative influence on the speed of absorption of carbohydrates. That's one reason why high fibre vegetables and fruits are at the base of the healthy Zone food pyramid. Fat also slows the absorption of a meal. Again, one of the reasons why fat is such an important part of every Zone meal. And the greater the ratio of fructose (fruit sugar) to glucose in a food the lower its glycaemic index will be, because fructose must be converted into glucose by the liver before it can be used, and that slows things up a bit. The glycaemic index of a mixed meal is usually just the average of the indices of its components.
One factor that doesn't affect a food's index is the configuration of its sugars, that is, if they're joined together in long chains, like in pasta, or if they're separate, like in sweet foods. This comes as a great surprise to most people because we've always been told that complex carbohydrates are healthy and simple sugars aren't, but the fact is that our tummies can't tell the difference between the two. Before any carbohydrate is taken up into the blood it must be broken down into simple sugars, and the rate that this occurs, that is, the glycaemic index, doesn't depend on the initial configuration. Complex carbohydrates are not healthier than simple sugars.
A big problem with food glycaemic index lists is that some of the best carbohydrates aren't even on them, and it's because of how the lists are devised. The glycaemic index of a food is calculated by comparing the rise in blood sugar after a fixed amount is eaten to that of a standard food (usually white bread or pure sugar). The amount used is usually equivalent to 50 grams of absorbable carbohydrate, which for low density foods - foods like high fibre vegetables - can be an enormous amount. For some foods, it's an amount too great for the volunteers in the laboratories to consume, and such foods are ignored. Because of this the reported range of "good" and "bad" indices is misleadingly shifted towards the "good" end. If you look at any of these lists you should take their "good" ratings as "moderate," their "bad" ratings as "very bad," and always remember that high fibre vegetables are the foods that actually have the low glycaemic indices.
The theory goes that if we eat foods with low glycaemic indices our blood sugar levels will remain more stable. Well that is certainly true, but what we're not told is that even when we choose low glycaemic index foods, if we eat too many of them at once, that is, if we eat a meal with a high glycaemic load, our blood sugar will still rise dramatically and we'll still require excessive amounts of insulin to deal with it. Our blood sugar levels won't be nearly stable enough because the insulin index of the meal is too high.
To effectively control our blood sugar levels we need to eat both suitable types and amounts of carbohydrates. We need eat meals with a low glycaemic index and a low glycaemic load. Only then will we reduce the need for insulin, and only then will we reap the health benefits that we're striving for.
The glycaemic load of a meal has a much greater effect on its insulin index than its glycaemic index, so the total amounts of carbohydrates that we're consuming should be the focus of our efforts if we're trying to control blood sugar levels. Even if we chose high indexed carbohydrates, if we don't eat too many of them our blood sugar won't be too out of control. Eating a small amount of "bad" carbohydrates is not unhealthy. But as we've just learnt, too many "good" carbohydrates are still bad for us.
Having said all of this, if we choose the really good carbohydrates, the vegetables that are high in fibre and therefore not very carbohydrate dense, we'll find it quite difficult to eat too many of them at once anyway. There are plenty of exceptions to watch out for though. Some breads and some pastas have low indices but are still very dense. Even some breakfast cereals are now claiming to be "healthy" because of their lowish index. Remember though that one bowl-full still delivers a high glycaemic load and therefore still has a dreadfully high insulin index.