The glycemic index or GI numerically ranks carbohydrates according to their effect on blood glucose levels. The concept, developed by Dr. David J. Jenkins in 1981 at the University of Toronto, says that choosing low GI carbs - the ones that produce only small fluctuations in our blood glucose and insulin levels - is the key to a healthy diet.

A GI value tells you only how rapidly a particular carbohydrate turns into sugar. (Recent studies indicate that neither protein nor fat have more than a minuscule affect on blood glucose.) It doesn't tell you how much of that carbohydrate is in a serving of a particular food. Therefore, you need to know both things to understand a food's effect on blood sugar. That is where the glycemic load (GL) factors in. The GL is a way to assess the impact of carbohydrate consumption that takes the GI into account, but gives a more accurate picture than does glycemic index alone. For example, the carbohydrate in watermelon has a high GI. But there isn't a lot of it in a slice, so watermelon's glycemic load is relatively low. When comparing GLs, a GL of 20 or more is considered high, a GL of 11 to 19 is medium, and a GL of 10 or less is low.

"Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control, and Disease." Gary Taubes's eye-opening book is a flow up to his provocative 2001 New York Times Magazine article, "What if It's All a Big Fat Lie?" A writer for Science magazine, Taubes begins by showing how public health data has been misinterpreted to villify dietary fat and cholesterol as the primary causes of coronary heart disease, diabetes, obesity, and other "diseases of modern civilization." Critical analysis he says, shows that these maladies are a result of increased consumption of refined carbohydrates eg., sugar, white flour and white rice, which raise glycemic loads.

When researcher John Yudkin announced similar conclusions in the 1950s, he was widely criticized. Taubes portrays the medical establishment as arrogant, using bad science, relying on excessive specialization, and demonstrating follow-the-leader sycophancy. The bottom line: Taubes cites clinical evidence showing that elevated triglyceride levels, rather than high total cholesterol, are associated with increased risk of heart disease, but measuring triglycerides is more problematic than measuring cholesterol. He believes the much maligned Atkins diet is the more promising path to weight reduction; a low-carb diet is more healthy than a low-fat one; and that restricting the consumption of certain carbohydrates is more important than counting calories.

The latest common wisdom on carbohydrates claims that eating so-called “bad” carbohydrates will make you fat, but University of Virginia professor Glenn Gaesser says, “that’s just nonsense.”

In an article in the October issue of the Journal of the American Dietetic Association, Gaesser analyzes peer-reviewed, scientific research on carbohydrate consumption, glycemic index and body weight and gives the first detailed review of the literature on the correlation between them. His findings run counter to the current consensus on the effects of “good” and “bad” carbohydrates.

Gaesser, author of “It’s the Calories, Not the Carbs” and other books, found that diets high in carbohydrates are almost universally associated with slimmer bodies. More importantly, Gaesser found that consuming lots of high-glycemic foods is not associated with higher body weights. In fact, several large studies in the United States revealed that high-glycemic diets were linked to better weight control. “There is no reason to be eating fewer carbs – they’re not the enemy,” says Gaesser, a professor of exercise physiology and director of the kinesiology program in the Curry School of Education.

The description of carbohydrates as “good” or “bad” is based on glycemic index, a measure of the quality of the carbohydrate in terms of how much it raises blood sugar. Foods having a high GI are generally thought to be “bad” because they raise blood sugar more than “good” carbs do. Proponents of the glycemic index claim that this leads to excessive insulin secretion, which can cause weight gain and health problems. Foods such as whole-grain breads are said to offer “good” carbs, because they have a lower GI than white bread, for example. Likewise, a glass of pineapple juice has a high GI compared to apple juice.

Several popular low-carb diets use glycemic index as a key feature for optimum weight control, but it is not a reliable description of carbohydrate quality, Gaesser says. Digestion is a complicated process. It’s very difficult to determine the GI of a whole meal, for instance, so it doesn’t really make sense to use GI or “glycemic load” - the glycemic index multiplied by the quantity ingested - as a guide to eating. After looking at hundreds of articles on large-scale studies using surveys or randomized, controlled trials, Gaesser says they show that “people who consume high-carb diets tend to be slimmer, and often healthier, than people who consume low-carb diets.” Even high-glycemic foods have a place in the diet, he said, attributing that to the overall higher quality of a high-carb diet, which includes more fiber-rich and other nutritional foods.

Gaesser also looked for a clear association between carbohydrate consumption and illnesses, such as type 2 diabetes, heart disease and cancer. He found no compelling evidence that avoiding carbohydrates with a high GI helps prevent these diseases and others. People with diabetes, as well as very sedentary women who are obese, may benefit from lowering their consumption of foods with a high GI, Gaesser says. Reducing any part of the diet (carbs or proteins or fats) will result in modest weight loss in the short term, if calorie consumption is reduced, he points out. But for long-term weight maintenance, a high-carb, low-fat diet is still the best bet, he said. [Dr. Glenn Gaesser,"'Bad Carbs' Not The Enemy," University of Virginia. ScienceDaily (02OCT07).]

UCLA researchers have found an extract in white kidney beans that may help the body stop carbs from breaking down into sugars - and if not burned off, stored as fat. A digestive enzyme in the body normally acts like scissors, literally cutting starches into little sugars. Phase 2 stops the enzyme from cutting, so the starches stay in the body as long fibers and are burned off quicker - making losing weight and keeping a normal blood sugar much easier. Patients in the clinical studies who took the pill, Phase 2, lost body fat, not lean muscle.

The extract is not recommended for pregnant women or type one diabetics because their blood sugar could get too low. Mild nausea is the only known side effect. The FDA recognizes Phase 2, but doctors say it isn't a miracle pill. Patients still need to watch what they eat and exercise. But at least they don't have to give up carbs for good. It is available over the counter at health food stores for about $25 a bottle.