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Nutrition News: Glycemic Index

Charlyn Fargo on

Glycemic Index

Should you care about a food's glycemic index?

Maybe, maybe not.

The glycemic index, simply put, is a measure of how quickly a food causes blood sugar levels to rise.

The measure ranks food on a scale of 0 to 100. Foods with a high glycemic index, or GI, are quickly digested and absorbed, causing a rapid rise in blood sugar. The foods that rank high on the GI scale are often -- but not always -- high in processed carbohydrates and sugars. Pretzels, for example, have a glycemic index of 83; and a baked potato without the skin clocks in at 98, according to the Academy of Nutrition and Dietetics.

Meanwhile, foods with a low GI are digested and absorbed at a slower rate, and, subsequently, cause a slower rise in blood sugar levels. These are typically rich in fiber, protein and/or fat. Examples of these include apples with a glycemic index of 28, Greek-style yogurt at 11, and peanuts at 7. However, keep in mind that a low GI doesn't mean a food is high in nutrients. You still need to choose healthy foods from all five food groups.

Diets centered on mostly low-GI foods can make it easier to achieve and maintain a healthy weight, since these foods keep us feeling fuller, longer. Low-GI diets also have been shown to improve insulin resistance, and lower glucose, cholesterol and triglyceride levels in people with type 2 diabetes.

One exception to the recommendation of a mostly low-GI diet is after intense or prolonged exercise. Consuming high glycemic foods can actually be more beneficial for muscle recovery, since they're rapidly digested.

But there's a problem putting too much stock in the GI -- A food's GI ranking only applies when a food is consumed on an empty stomach without any other type of food. That isn't always how we eat. We may have a bag of pretzels as a stand-alone snack, but we typically don't eat just a plain potato with nothing else. If we add a lean steak or a piece of salmon, a side of broccoli and a salad with vinaigrette, and the protein, fiber and fat all serve to lower the glycemic index of the meal.

In addition, the glycemic index doesn't take into account how much food is actually consumed. The GI value of a food is determined by giving people a serving of the food that contains 50 grams of carbohydrate minus the fiber, then measuring the effect on their blood glucose levels over the next two hours.

A serving of 50 grams of carbohydrate in one sitting is reasonable for a food such as rice, which has 53 grams of carbs per cup. But for beets, a GI ranking of 64 is a little misleading. Since beets have just 13 grams of carbs per cup, a person would need to consume nearly 4 cups of beets in order to cause that spike in blood sugar levels.

A better approach is to use the glycemic load, or GL, a formula that corrects for potentially misleading GI by combining portion size and GI into one number. The carbohydrate content of the actual serving is multiplied by the food's GI, then that number is divided by 100. So for a cup of beets, the GL would be: 13 times 64 = 832 divided by 100 = a GL of 8.3.

As a frame of reference, a GL higher than 20 is considered high, between 11 and 19 is considered moderate, and 10 or less is considered low.

The bottom line: Look for the glycemic load. Use the glycemic index as a tool to identify lower-glycemic foods that are more nutrient-dense, as well as higher glycemic foods that are higher in refined carbohydrates.

Q and A

Q: Can garcinia promote weight loss?

A: Effects of Garcinia cambogia, a tropical fruit, have been promoted for weight loss for years. The fruit is a source of hydroxycitric acid (HCA), which is also an ingredient in many diet formulas. Test-tube and animal research suggests that garcinia extract and its HCA in particular, may help promote weight loss by suppressing appetite and inhibiting the storage of excess calories from carbohydrates as fat. But there has bene little good human research on garcinia. Moreover, HCA is short acting and would have an effect only when consumed during the hour before eating meals high in carbs (not fat). Even then, the effect may not be significant. A meta-analysis of 12 clinical trials, published in the Journal of Obesity in 2011, found that garcinia extract produced only very small changes in weight. And the researchers noted that the studies reviewe3d were short (none longer than 12 weeks), small and rife with methodological problems. Plus they found side effects, including nausea and headaches. In a 2014 study in Phytotherapy Research, researchers looked at 43 overweight or obese women who took garcinia extract or a placebo daily for two months. There was no significant change in weight or body composition. What's most concerning about garcinia are possible adverse effects in the liver, as described in human case reports and animal studies. For instance, an animal study in the World Journal of Gastroenterology in 2013 found that garcinia can induce liver damage by increasing inflammation, free radicals and the formation of excess connective tissue. In at least two case reports, people taking garcinia developed liver failure and required a liver transplant. Give the potential serious risks and the lack of evidence of meaningful benefits, we recommend avoiding garcinia and diet formulas containing it. -- University of California, Berkeley Wellness Letter

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Charlyn Fargo is a registered dietitian at Hy-Vee in Springfield, Ill., and the media representative for the Illinois Academy of Nutrition and Dietetics. For comments or questions, contact her at charfarg@aol.com or follow her on Twitter @Nutrition Rd. To find out more about Charlyn Fargo and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.


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