What’s the Glycemic Index, and Should You Care?

Carbs Today’s post addresses this question from a regular reader of the blog: “Glycemic index – does that matter? A lot of “good” carbs (whole grains) seem to have really high glycemic index.”

For those who don’t know, the Glycemic Index is a carbohydrate ranking system that was developed over 30 years ago in an effort to classify foods according to how quickly they introduce sugar into the bloodstream. A lower number on the Index means that sugar is released into the bloodstream more slowly, while a higher number means the food could potentially cause blood sugar to “spike,” having negative effects on the body’s insulin response.

Early on, there was much excitement in the scientific community, because studies of single foods, usually conducted on rodents, showed great promise in terms of regulating blood sugar and insulin response. Over the years, however, a number of drawbacks have been found. The biggest problem is that we almost never eat just one food by itself, so a lot of the benefits associated with eating a low-GI food are undone when that food is naturally paired with other, higher-GI foods in a recipe or meal. A second problem is that the Index is based on a serving size containing 50 grams of available carbohydrate (or 25 grams for lower carb foods). This means that a “serving size” for the GI can be starkly out of line with typical serving sizes in a normal diet. For example, to get 50 grams of carbohydrate from raw carrots, you’d need to eat about 1.75 pounds (that’s nearly two bags of baby carrots), but to get 50 grams of carbs from whole wheat bread, you’d only need to eat two slices. So, the Glycemic Index could be considered accurate in a useful way for whole wheat bread, but not for carrots.

To rectify this problem, researchers in the GI camp created the Glycemic Load, which applied the Index to normal serving sizes of carb-containing foods. This is much more useful, but still has its limitations. For one thing, it still only considers individual foods. Also, method of preparation can vastly alter GI and GL values (any processing or cooking normally makes a food move higher on the Index). Finally, food labels don’t list GI or GL values, so if you really want to pay attention to this, you have to do a lot of research on your own. Might it be worth it to do that research? That largely depends on your dietary concerns.

For individuals diagnosed with or at high risk for Type-2 Diabetes (T2D), the Glycemic Load can be a useful way to keep blood sugar levels and insulin regulation in check. But that’s pretty much where the benefit stops. A 2014 review of relevant research published in the American Journal of Clinical Nutrition found that following a low-glycemic diet had no effect on BMI, obesity or heart disease. What’s more, the studies reviewed showed a much stronger correlation between BMI and T2D than between GI or GL and T2D. In other words, individuals who ate a high-glycemic diet but who were not overweight were at a relatively low risk for Type-2 Diabetes.

What the study didn’t look at, but what is probably of interest to many of us, is the effect that high- or low-glycemic foods can have on our energy levels. Indeed, eating foods that quickly spike blood sugar levels can be taxing on our bodies’ systems and leave us feeling jittery and then lethargic. So it could be useful to choose lower-glycemic single foods for between-meal snacks. Eating an apple would be much better than eating a cup of fresh pineapple, for example. If you’re interested in seeing where some of your favorites fall, here’s a handy list. Just be sure that you’re comparing like foods when you use the list. The reader’s initial observation, that whole grains tend to be higher on the Glycemic Index, is only true when comparing them to non-grain items. Brown rice, for example has a higher GI and GL than grapefruit or yogurt, but it’s much lower than white rice. Of course, foods without carbohydrate (fish, meat, poultry, oils and other pure fats) have a GI and a GL of zero, so working small amounts of them into your diet can naturally help stabilize blood sugar.

Perhaps the best guidance on Glycemic Index, though, comes from the Mayo Clinic, which advises us to choose foods higher in fiber, such as whole grains, legumes, vegetables and some fruits, and to eat them raw or as minimally processed or cooked as possible. This way, all your meals and snacks will naturally be lower on the Index, giving you a nice, sustained release of energy throughout the day.

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