Pizza

Many people have noticed that pizza seems to keep their blood glucose level high longer than just about any other food. While the reason remains a mystery, this folk wisdom now has scientific confirmation.

Ahern et al. compared the effect on insulin-dependent patients of a pizza meal with a control meal that included high glycemic index foods. They found that although the initial glucose increase was similar for the two meals, the GI continued to rise and was significantly increased from four to nine hours after the pizza meal compared with the control meal.
 

Rice and Potatoes

Rice and potatoes are some of the foods most tested for their glycemic indexes. They are important both because most of us tend to eat a lot of rice and potatoes and because they can have a high glycemic index. Professor Brand-Miller reports the results of 49 studies of rice and 24 studies of potatoes. The results for rice ranged all the way from 54 to 132 and for potatoes from 67 to 158.

What could possibly cause such tremendous variation? According to Professor Brand-Miller, for rice one of the most important considerations is the ratio of amylose to amylopectin. She says that "the only whole (intact) grain food with a high G.I. factor is low amylose rice, such as Calrose rice...However, some varieties of rice (Basmati, a long grain fragrant rice, and Doongara, a new Australian variety of rice [which is not available in the United States] have intermediate G.I. factors because they have a higher amylose content than normal rice."

Wallace Yokoyama, a research chemist working for the U.S. Department of Agriculture in Albany, California, gave me a comprehensive explanation. There are, says this noted rice specialist, four types of rice: long-grain, medium-grain, short-grain, and sweet rice. Sweet rice is also known as sticky or waxy rice. It makes the best sauces and gravies, and is usually the rice used in Asian restaurants. Sweet rice has no amylose, Yokoyama says. In other words, it is the rice that has the highest glycemic index. The three other types of rice have lower glycemic indexes. Among these types, long-grain rice has the highest amylose content and short-grain the lowest.

Of course, each of these three types of rice may be brown or white. Brown rice has a lower glycemic index than white rice, everything else being equal. Therefore brown long-grain rice—or if you can find it—brown Basmati rice—will probably be your best bet for a rice with a lower glycemic index. White Basmati rice had a glycemic index of 83 in one study. Brown Basmati rice can be expected to have a somewhat lower index, but we don't know precisely what it is, because the studies haven't been done yet.

Richard Jackson maintains in e-mail to me that my statement that there are three basic types of rice is "somewhat incorrect." He says that there is also a sweet rice used in oriental cooking. "It is not only very much stickier than standard Asian milled rice (such as Kokuro Rose Brand)," he writes, "but is perceptibly sweeter when eaten. It is typically fermented prior to cooking, whereas standard Japanese-style milled rice is not. I think if more research is done into this factor, the data may prove that the difference between sweet rice and regular Asian-style rice is different on the scale of caloric values as pertains to ingestion by diabetics."

Among potatoes, new and some white potatoes have the lowest indexes. The reason that new potatoes have a lower GI is probably because most of the amylopectin is less branched—it is more like amylose at this immature stage.

Fructose and High Fructose Corn Syrup

An addition to the published glycemic indexes is high fructose corn syrup, which is endemic in U.S. processed foods. Fructose is not the same as high fructose corn syrup, Professor Jennie Brand-Miller emphasized. "The former is pure fructose; the latter [high fructose corn syrup] is a mixture of fructose and glucose," she wrote. "In high fructose corn syrups, the fructose content is about 50 percent. Thus the GI of high fructose corn syrups is about the same as sucrose, i.e. 60-65 (if glucose = 100)." When white bread = 100, the GI of high fructose corn syrups is 85-92.