Clarifying "Glycemic"

It is an inevitable consequence of becoming a big geek about some subject that, when marginally knowledgeable people write/speak about your area of interest, they make errors which have the mental effect of Freddy Kruger's hand running down a blackboard. For me it is the misuse of nutrition terminology.

Currently setting my teeth on edge is the bandying of the term "glycemic," and its two compound words "glycemic index" and "glycemic load." You can barely turn on the television without some diet club or other trumpeting that they've "Unlocked the science of the glycemic index!" or use "low glycemic carbs!" The popular press, too, tosses the terms around, often adding that "low glycemic carbs" include "fruits, vegetables and whole grains." Since this last is so wrong-headed as to be dangerous, and because I have a book coming out any second now called The Glycemic Load Diet Cookbook, and because I have taken some heat for using the term "low glycemic load" along with or instead of "low carbohydrate," it seems important to set the issue straight.

(Yes, I have covered this subject before. But I get new readers every day -- Hi, guys! -- and, thank heaven, people are still figuring out that cutting carbs is a better bet than cutting fat. So I'm going through this again. If your eyes are rolling back in your head from boredom, go read somebody from the Blogroll, instead. And come back soon!)

The word "glycemic" is the easiest: "Having to do with glucose (sugar) in the blood." That's it. So when advertisers or journalists speak of "low glycemic carbs," they think, at any rate, that they're talking about carbs that have a modest effect on blood sugar. Whether they're correct is another question.

"Glycemic index" (GI) was the next concept to arise, and it refers to how quickly the carbohydrate in a food is absorbed into the bloodstream, and therefore how quickly and sharply it raises blood sugar. For a while it was felt that simply restricting the diet to carbs with a modest glycemic index would, for many people, reap the benefits of carb restriction. However, it has begun to appear that this is not so. Why?

Because the glycemic index does not actually predict the effect of foods on blood sugar levels. Why not? Because it does not take into account how much carbohydrate is in the food.

It has to do with how the glycemic index numbers are derived. A group of people is tested for fasting blood sugar. The subjects then eat a portion of the food to be tested that has been carefully measured to contain fifty grams of digestible carbohydrate. Their blood sugar is then tested at regular intervals, and the results are averaged out to give a ballpark figure for the food's glycemic impact.

Do you see the problem? It lies in that "fifty grams of digestible carbohydrate" thing. Because that's not how we eat food.

Some foods just plain contain more carbohydrate than others. And it is the amount of carbohydrate, even more than the glycemic index, that will determine blood sugar levels. Pure glucose has the highest glycemic index of any food -- indeed, it is often the food against which other carbohdyrates are rated. But what would happen to your blood sugar if you ate just 1 gram of glucose? Not a thing, that's what.

The glycemic index can make good foods look bad. Far worse, it can make bad foods look good.

Take, say, beets. Beets have a glycemic index of 64, pretty darned high for a vegetable. But how many beets would you have to eat to get 50 grams of digestible carbohydrate? FIVE CUPS, that's how many. A half-cup serving of beets has just 5 grams of usable carbohydrate. Glycemic index or no, it's just not going to raise your blood sugar much. If you like beets, what the heck, have a few.

Whole wheat spaghetti, on the other hand, has a glycemic index of just 37. But how much would it take to get to the fifty-gram mark? If you had a modest dinner portion of one cup of whole wheat spaghetti with a half-cup of spaghetti sauce, you'd have eaten fifty grams of digestible carbohydrate. Despite the low glycemic index, that plate of "healthy, low glycemic" whole wheat pasta is going to jack your blood sugar up much higher than a half-cup of "high GI" beets.

Enter the concept of the glycemic load. Developed to put those GI numbers into a real-world context, the glycemic load simply multiplies the glycemic index of a food by the actual number of grams of carbohydrate eaten, to give a meaningful estimate of how much a given food will derange your blood sugar.

Let's look at our beets and spaghetti again. The beets have a GI of 64, and 7 grams of total carbohydrate. 64 x 7 = 448. Since GIs actually have a decimal point (ie .64), our beets have a glycemic load of just 4.48, very low. How about our spaghetti? The spaghetti itself has 37 grams of carb in it (the rest comes from the sauce), so 37 x 37= 1369, or a glycemic load of 13.69. I couldn't find a glycemic index for spaghetti sauce, but plain tomato sauce is a 64; near enough. (Probably low, actually, since most spaghetti sauce has added sugar.) 1/2 cup spaghetti sauce has 20 grams of carbohydrate. 64 x 27 = 1280, or a glycemic load of 12.80. So our "healthy, low glycemic" supper of whole wheat spaghetti has a glycemic load of 26.49, quite high. Your blood sugar will feel it, trust me.

For the record, a glycemic load of 10 or below is "low." 11-19 is "medium." Anything over that is high. Really high. What should your glycemic load for a meal or for the day be? I can't tell you that, any more than I can tell you how many grams of carb per day you should eat; bodies vary.

The point is that despite all that blather about it being fine to eat lots and lots of "low glycemic carbs," a low glycemic load diet will, perforce, also be a diet low in total carbohydrate. A low carbohydrate diet is a low glycemic load diet, and a low glycemic load diet is a low carbohydrate diet. No other way to do it.

(For the record, most whole grain foods don't have a particularly low glycemic index, much less a low glycemic load. Whole grain cold cereals are all sky-high. Most whole grain bread is not much lower. Even brown rice has a glycemic index of about 60. And, of course, they are one of the most concentrated sources of carbohydrate. Whole grains cannot be more than a tiny part of any low glycemic load diet.)

So why use one term over the other? If you hadn't noticed, I do still use the term "low carb" quite frequently. It's short, it's to the point, it's accurate. However, it cannot be missed that there has been a media backlash against the term, and an embrace of the "glycemic" terminology. If by using the currently acceptable term -- while clarifying what it really means -- I can get people to listen who would automatically turn off at the term "low carbohydrate," then that is an important thing for me to do.

Giving people life-saving information is the important thing. Low carb, low glycemic load. Either way, it saves lives.