The Glycemic Index, Ungarnished

How to measure glycemic measures

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I have long observed that food, or at times pseudo-food, is often garnished with far better food. In fact, the bright green curlicues of leafy greens and herbs (e.g., kale and parsley) are some of the most nutritious foods on the planet. Eat the garnish, skip the food—and you might just live forever!

But the way we garnish information about food is another matter altogether. Food for thought may start out quite wholesome, but get garnished along the way with a whole array of sales pitches and marketing distortions. The result can be rather unpalatable.

With that in mind, I write today to ungarnish the glycemic index.

Some weeks back, I provided an overview of the glycemic index and the glycemic load (for the differences between them, please refer to my prior column). Since then, these terms have appeared numerous times in both the scientific literature and pop-culture publications. A Google News search retrieves dozens of references in the past month alone.

Given the preoccupation with all things glycemic, the topic deserves some additional consideration here, too—but this time, as pledged, totally ungarnished. Let's just talk about what we all should and shouldn't do with these glycemic metrics.

DO NOT use them as a reason to jettison any fruits or vegetables from your diet. In 20 years of clinical care, I have yet to meet a single patient who can legitimately blame obesity or diabetes on eating too much produce of any variety.

It's true that some fruits and vegetables have a relatively high glycemic index (GI), although they generally have a much lower glycemic load (GL). But who cares? The net effect of eating more fresh produce is consistently better health, not worse. Fad diet authors who have advised against eating fruits or certain vegetables to adhere to low-GI eating have done the public a disservice, however they may have profited.

Which leads to the second item: DO NOT mistake a glycemic measure for a measure of overall nutritional quality. Fresh fruits and vegetables are generally really good for us, whatever their glycemic scores. Crisco—pure trans fat—is in no way exonerated by its glycemic scores of zero. Don't forget what these measures do and don't measure.

DO NOT confuse a low-GL diet with a low-carb diet. As I pointed out before, at least one study has directly compared different ways to achieve a low-glycemic diet, and the diet comprised of mostly plants and high-complex carbohydrates had the best metabolic effects overall. Various studies of such diets by David Jenkins, who invented the glycemic index in the first place, suggest much the same.

The glycemic load is a useful consideration when choosing among foods made from grains or with added sugars. The information can be hard to find, but it would be genuinely useful to know this measurement when choosing breakfast cereals, breads, pastas, crackers, chips, cereal bars, processed dairy products, and dessert items. In general, a bread or cereal with a lower glycemic load is a better bread or cereal. If you have the means to factor the glycemic load into such choices, by all means DO SO.

The glycemic load is also useful in terms of single meals, not the whole diet. It is the dietary pattern, not a food in isolation, that is most likely to exert a meaningful influence on health. Almost all diets associated with good health outcomes—from vegan and Paleo to traditional Asian and Mediterranean—have a low glycemic load overall; they just get there in different ways. At the level of meals, foods interact. Studies have shown, for instance, that a high-fiber intake at breakfast can blunt substantially the glycemic responses to foods consumed at lunch.

But there is no need to aim for a low-GL diet, per se. Rather, aim for a diet of whole, natural foods, mostly plants. The result will be virtuous and salutary in many ways, a high level of fiber and a low glycemic load reliably among them. Whereas aiming for a plant-based diet of real, wholesome, simple, minimally processed foods will lead to a low glycemic load, aiming for a low glycemic load will not necessarily lead to such a diet. It might well lead to the deli case.

In the full throes of the holiday season, food is much on everyone's minds: those who eat it, those who prepare it, those who sell it, and those who talk about it. Even as many of us wrestle with the challenges of dietary restraint through a gauntlet of parties and family gatherings, a new crop of diet books is ready to greet a new crop of New Year's resolutions directed at fixing the damage we just did. It's a triumph of hope over experience if ever there was one.

Amid the season's holiday parties, I suggest you consider eating less of the food and more of the garnish. Honestly, it grows on you!

But garnish has not served the glycemic index nearly so well. Since its development, the glycemic index, and then the glycemic load, have been garnished with various applications of salesmanship. The measures are sound, and offer utility, but only when such distractions are discarded. So in their case, put them to judicious use—but skip the garnish!

Hungry for more? Write to eatandrun@usnews.com with your questions, concerns, and feedback.

David L. Katz, MD, MPH, FACPM, FACP, is a specialist in internal medicine and preventive medicine, with particular expertise in nutrition, weight management, and chronic-disease prevention. He is the founding director of Yale University's Prevention Research Center, and principal inventor of the NuVal nutrition guidance system. Katz was named editor-in-chief of Childhood Obesity in 2011, and is president-elect of the American College of Lifestyle Medicine.