Many people have heard of the glycemic index (GI), but they are not exactly sure what it means, or how it works. A low glycemic index diet is thought to significantly lower your risk of type 2 diabetes, obesity, coronary heart disease and even certain cancers. This is probably true, but not for the reasons people think.

The GI measures how quickly a fixed amount of food (50 g) gets absorbed into your bloodstream and raises your blood sugar. Developed at the University of Toronto, it correlates with the amount of insulin required to escort that blood sugar to the cells of your body. The faster you absorb a food, the more insulin you need to catch it and escort it to the cells. The glycemic index, in other words, predicts how much insulin is required to absorb various foods. If your goal is to conserve insulin to the greatest extent possible (so you have enough to keep your blood sugars normal over your entire lifetime), then you’ll want to shift your food choices to ones with lower GI’s.

The glycemic index ranges from 0 to over 100. Consider a low GI as below 40, and a high GI as above 70. Consider results between 40 and 70 as mid-range. Here are some actual ratings. 

Let’s take a look. First, notice which foods are rated lowest. Most beans are very low (except baked beans, which contain gobs of sugar). Most green (broccoli, celery) and white (cauliflower, mushrooms) vegetables are very low, below 25. Red, yellow, and orange vegetables lie in the mid-range. Tomato juice, in comparison, has a GI of 38. Generally speaking, beans, vegetables, and dairy have some of the lowest glycemic indexes. Plain yogurt has a GI of 14. All carbohydrates are not created equal.

Crackers and cookies are higher (60’s-80’s) because they are made from white flour; oatmeal cookies (55) are a little better. Breakfast cereals tend toward a similar range (70-80), except for a few whole-grain products in the 50’s. Fruits are better, in the 30-50’s, though some (especially tropical fruits) are higher. But don’t worry, I promise that fruit is not what’s causing the diabetes and obesity epidemics in our country.

Other items with high GI’s include ultra processed Poptarts (72), Rice Chex (89), french fries (75), pretzels (83), tofu frozen desserts (115) and sugar drinks like Gatorade (78). Instant rice (87) (it’s pre-digested) is much higher than steamed brown rice (50). Whole-grain breads are much lower (40) than white breads (60-70) or baguettes (94). Whole-grain breads have more fiber and lower GI values, but beware: Brown breads are sometimes treated with enzymes to break apart fiber and soften the crust, which then raises the GI.

The GI is also affected by two related factors: 1) other foods eaten at the same time, and 2) preparation methods. Fiber, fat and protein all slow gastric emptying, which is why it’s a good idea to sprinkle peanuts on your oatmeal, or olive oil on your green beans. Vinegar and lemon juice also appear to slow gastric emptying and, thereby, reduce rates of absorption. Wine and spirits (but not beer) taken with a meal may reduce the glycemic index of that meal by 15%. But why are instant mashed potatoes a whopping 74? The physical action of mashing starts the process of breaking down food long before you swallow it. The less work your body has to do, the more rapidly you absorb the food, and the higher the GI.

The good news is that you can affect the rate at which you absorb certain foods. Whatever increases the work of breaking down food will lower its GI and vice versa. The longer it takes to break down a food, both mechanically and chemically speaking, the lower its GI. The work of chewing up, teasing apart, and breaking up the fibers of an apple is just that — work.

Limitations of the glycemic index? It measures only glucose, and not fructose, a major cause of insulin resistance, high triglycerides, and fatty liver. Also, all results are based on intake of a 50-gram serving size, even if the usual serving is much smaller. But, overall, shifting your food choices to items with lower GI ratings should help to conserve your insulin, and that, my friends, is the name of the game.