Dr. Kracker

A Carb Catalog

As sales of “low-carb” foods have taken a nose dive, the latest buzz has been about “low glycemic index” foods. Proponents claim that these foods can help you lose weight more easily and help prevent diabetes and heart disease. The scientific concept of the glycemic index was proposed 25 years ago as a way to help control diabetes. What’s new is applying it to everyone in every-day eating, which is not easy to do…

A simple explanation…
The glycemic index (GI) ranks carbohydrate-containing foods (grains, fruits, vegetables, dairy) by their effect on blood sugar. Foods with a high glycemic index (on a scale of 0 to 100) are those quickly broken down into glucose (sugar), which leads to a rapid rise in blood sugar and a corresponding high demand for insulin. Insulin is the hormone that moves glucose from the blood into cells where it is used. Eating foods low on the index can result in fewer spikes in blood sugar and insulin. In general, sugary refined foods, refined grains (such as bread made from white flour), and potatoes rank high; unprocessed whole grains, beans, and nonstarchy fruits and vegetables rank low to moderate. A related concept is the glycemic load, which adjusts for the amount of carbohydrate in a single serving of food.

…But it’s not that simple
First it’s not always obvious where a food ranks on the glycemic index. You might think that foods highest in sugar would cause blood glucose to shoot up most, but that’s not always the case. Instant rice is at the top of the list, along with white potatoes, watermelon, raisins, carrots, pretzels, rice cakes, most breakfast cereals, and white bread, whereas ice cream ranks low.
Moreover, the glycemic index measures food in isolation under fasting conditions, which is not how we eat. Rather, a meal contains a mix of foods, which can make the glycemic response unpredictable. Fat, protein, and fiber in a meal lower the glycemic index of individual foods. How a food is stored, processed, and cooked also affects its glycemic rank. If you eat potatoes with cheese, for example, or eat them as chips, they are digested more slowly. Different types of pasta and rice have different GIs, as go different varieties of certain fruits and vegetables. As fruit ripens, its GI decreases, surprisingly. If you mash a potato, its GI goes up. Adding vinegar to a food can reduce GI.

To further complicate the picture, not only are there variations in response from one person to the next, but even the same person may respond differently to the same food from day to day.

GI Bill of Health?
Low- GI diets have been touted for weight loss, as well as for preventing diabetes, heart disease, and other conditions. But studies have yielded inconsistent results. Such diets may be protective, not so much because of their low GI, but because they also tend to be rich in nutrients, phytochemicals, and fiber. And people who chose low-GI foods may have other healthy habits. Here’s what we know:

Weight loss. High-GI foods cause a rapid rise in blood sugar, which triggers a spike in insulin. Theoretically, this may lead to weight gain- by increasing fat storage, reducing fat burning, and or increasing appetite. But the evidence is mixed. Some studies show that low-GI diets help promote weight loss, while others do not. One complication is that the glycemic index does not always accurately predict how much insulin the body will release in response to blood sugar. For example, lentils (low on the index) provoke higher insulin levels than potatoes (high on the index). When it comes to weight, portion size (that is, calories) is more important than the specific foods a person eats. Its also hard to separate out other food-related factors. For example, low-GI foods tend to be high in fiber, which may help in weight control.

Diabetes. Some research suggests that high-GI diets are more likely to lead to Type 2 diabetes. But again, the evidence is mixed. If certain foods do play a role in diabetes, it may simply be that people eat too much of them and gain weight. Moreover, the fiber in most low-GI foods may be what’s largely protective. The European Associate for the Study of Diabetes advises people with diabetes to substitute low-GI foods for high-GI foods when possible. In its latest guidelines, the American Diabetes Association concludes that it’s unclear whether a low-GI diet can reduce the risk of diabetes, but it encourages the consumption of low-GI foods that are rich in nutrients and fiber.

Heart Disease. Several large population studies have linked high-GI diets to increased risk of heart disease. And low-GI diets have been shown to improve triglycerides and cholesterol in some people more than conventional low-fat diets. One theory is that high blood sugar leads to inflammation and damages blood vessels. But a 2004 review of 15 studies, the Cochrane Collaboration concluded that there is insufficient evidence to support the use of low-GI diets for heart health.

Putting it in to practice
The glycemic index is an interesting and possibly important way of thinking about what we eat. But from a practical perspective, it makes eating unnecessarily complicated. Simply following the guidelines of a healthful diet (eating more whole grains, beans, fruits, and vegetables, increasing fiber, and cutting back on sugary and highly processed convenience foods) makes for less glycemic impact in general. Moreover, several foods that are high on the glycemic index – carrots, potatoes, watermelon, and dates, for example – are very nutritious and can be included in a healthy diet. If you’re trying to lose weight, the bottom line is that calories count more than the glycemic index. In fact, diets that incorporate elements of the glycemic index. Such as Atkins and South Beach, heave one thing in common. They get you to cut calories, even as they tell you that calories don’t count. . (University of California, Berkeley Wellness Letter, Volume 23, Issue 3, December 2006)