Once upon a time, carbohydrates were good, as long as they were low in fat and sugar. It was fat that made us fat.
In the late 1990s, carbohydrates became bad and had to be rationed, and fat made us skinny. Do we finally have carbs right? Do we have their number? More importantly, is that number the glycemic index (GI)?
In 1981, David Jenkins and colleagues at the University of Toronto developed a method to rank carbohydrates according to their immediate impact on blood glucose as a guide for diabetics. It was christened the "glycemic index."
The theory behind glycemic index is simple: As blood sugar rises after eating carbohydrates, insulin - secreted by the pancreas to metabolize sugar - rises in response. If you can predict the effect of eating different carbohydrates, you can avoid sharp insulin peaks and control blood sugar more effectively.
|Solo GI was the first clinically validated, low-glycemic line of nutrition bars on the market.
It certainly is a tool for diabetics. "More than 17 million people in the U.S. have been diagnosed with type 2 diabetes, and this number continues to grow at a rate of 6 percent per year," says a whitepaper by Ardsley, N.Y.-based Danisco Sweeteners (www.danisco.com/sweeteners). The paper promotes sweeteners with "low glycemic benefits," specifically the ingredient supplier's Litesse polydextrose, Lactitol and Xylitol.
At some point, glycemic index made the jump from a diabetic tool to a weight-loss regimen. It was gradual, actually, but picked up a head of steam after the demise of the Atkins Diet. In one best-selling diet book after another, low GI is now supplanting the low-carb message left over from the recently deceased "carbs bad, fat and protein good" fad.
Here again, the theory seems sound. If sugar enters the blood too rapidly, insulin will spike, cells will grab glucose too quickly to be used for immediate energy, thus favoring the storage of fat. Blood sugar will then drop dramatically, leaving you hungry for more carbohydrates. This will make overeating and obesity inevitable.
Many natural carb sources, such as beans and most whole grains, have a low GI. Lots of refined carbohydrates like white bread have a high GI. Many health experts believe there is a close link between the modern diet of highly refined foods and the epidemic of obesity and type II diabetes. So with low-carb mania dying and obesity still raging, many food manufacturers are stepping up to meet the demand for low-GI products.
At the same time, there are incongruities. Chocolate fudge cake has a GI of 38, almost identical to pinto beans with a GI of 39. Boiled potatoes, by far the most satisfying food on the satiety index, is at 101, while potato chips and pound cake are 54. Fava beans are at 79, higher than a donut with cinnamon and sugar at 76, and nearly the same as jelly beans at 80.
Silver bullet or blank?
Some believe glycemic index is the silver bullet that will pull us out of the obesity trap. "I believe eating low-glycemic nutrition can address the growing, dual epidemics of diabetes and obesity, 'diabesity,' head-on," says Saul Katz, president of Solo GI Nutrition (www.solo-gi.com), Edmonton, Alberta.
"The glycemic index is a very important new tool that can help manufacturers become part of the solution, instead of contributing to the problem, by designing foods that deliver energy to our bodies as nature intended," Katz continues. "That is why we developed Solo GI Low Glycemic Nutrition Bars, to address the need for sustained energy and hunger management between meals or on the run."
Solo GI was the first clinically validated, low-glycemic line of nutrition bars on the market. The product was honored by the Specialty Nutrition Group as the Most Innovative Product of 2004.
Despite the enthusiasm, GI is a concept with issues, not the least of which is the fact that GI is not an inherent property of food. GI is a measure of the impact on blood sugar over a two-hour period after eating 50g of a test food.
This measure is compared with that of 50g of a reference food (glucose or white bread), and expressed as a percentage of the reference - assigned a value of 100. The number is an average taken in only 10 subjects. A score of 70 or above is considered a high GI, 55-69 is medium and 54 and below is considered low GI.
Many factors affect GI, including fat, protein, fiber, food particle size, cooking method, moisture content, type of starch (amylose or amylopectin) and type of sugar (for example, glucose or fructose). GI can vary from lab to lab, person to person and even in the same person at different times of the day. This makes standardization difficult, if not impossible.
|Kellogg's Kashi Go Lean rolls do not tout a low GI, but are marketed as providing "optimized glycemic response."
The fact that so many different factors affect GI, contrasted with the basic premise that it's desirable for sugar to enter the blood slowly, has led to many approaches to creating low-GI products. Kellogg Co.'s Kashi Go Lean rolls (www.kashi.com) are marketed as "optimized glycemic response."
Go Lean rolls were created around the aspect of glycemic load (GL), the relation of GI to grams of carbohydrate. Many nutritionists feel GL gives a more realistic picture than GI because we eat mixtures of ingredients, all of which affect blood glucose. Others point out foods with the same GL may vary significantly in glycemic response.
"Desired" GI numbers often are achieved by the use of novel sweeteners with a very low GI. For example, Danisco offers a line of sugar alcohols and "randomly bonded glucose polymers" that are incompletely broken down in the small intestines.
Another strategy used to lower GI in foods is to replace sugars with non-digestible fructose polymers, which also act as prebiotics. Two examples, Raftiline and Raftilose by Orafti (www.orafti.com), Malvern, Pa., are prebiotic ingredients used in a wide range of food and beverage products.
Because of the complexity and the controversy that has accompanied GI, some manufacturers feel it's confusing to place GI numbers on the label. "Glycemic index is a tool that can be used in the present-day struggle with being overweight and obese, but it's just one tool," says Gerry Amantea, vice president of technical service for Hain Celestial Group Inc. (www.hain-celestial.com), Melville, N.Y. "If a low-glycemic snack can help a person sustain energy between meals so that at the end of the day fewer calories are consumed, the snack is a beneficial addition to the diet. In the end, it's 'calories in, calories out' that counts."
The Hain Celestial Group has developed a new line of low-GI products, called "Low G," in its Estee brand of sugar-free foods and snacks. The company spent decades creating foods that have been ahead of the trends in "healthy" carbohydrates and fats. "Although the Low G products all have been stringently tested for glycemic load, they will not carry glycemic index numbers, which at this point we feel overcomplicates a simple concept," says Amantea.
Some manufacturers find the rapid move toward GI mania troubling. Lara Merriken, CEO and founder of Humm Foods Inc. (www.larabar.com), Denver, worries about the message sent by placing glycemic index on the food label. Creator of the Lärabar line of organic raw food bars made with whole fruits and nuts, Humm Foods plays up the products, not the numbers.
"While I understand GI is trying to give people a measure, I also believe GI can steer consumers toward following a diet regimen that only focuses on GI and not on the quality of the ingredients in the product," Merriken says.
Rhonda Witwer, business development manager-nutrition at National Starch Food Innovation (www.foodinnovation.com), Bridgewater, N.J., agrees. "The quality of carbohydrates in our diet does matter, but focusing on glycemic index instead of the food components, such as dietary fiber or natural resistant starch, is a step in the wrong direction," she explains. "GI tells only part of the story. It does not indicate the effect of foods on insulin - the critical biomarker for maintaining healthy blood-sugar levels. Studies show glycemic index and glycemic load do not increase insulin sensitivity. In contrast, increasing dietary fiber and natural resistant starch are proven strategies for improving insulin sensitivity, which is the underlying biomarker for metabolic syndrome."
Can glycemic index deliver on its promise to stem the tide of obesity and type II diabetes? Or is it simply so seductively plausible it's been prematurely deemed the wave of the future? Both the Food and Agriculture Organization of the United Nations and the World Health Organization have endorsed glycemic index for use in classifying carbohydrate-rich foods and in guiding dietary choices.
However, U.S. health organizations are not so mesmerized. "Despite the increasing popularity of GI, its validity and practicality remain controversial, especially in the U.S.," writes Katherine Beals, nutrition professor at the University of Utah and consultant for the U.S. Potato Board, in a critical review of the glycemic index. "Currently, the American Diabetes Assn., the American Heart Assn. and American Dietetic Assn. do not recognize the GI as a useful dietary planning tool for weight management or disease."
A statement by the American Diabetes Assn. published in September 2004 concluded that observing GI along with total carbohydrate can provide additional benefit for blood sugar control, but the role of low-GI foods in preventing the development of type II diabetes was unclear. Here, preventing obesity was the most important factor.
As reasonable as the connection between high-GI foods and obesity seems, there is as yet no definitive evidence that this theory is correct. There are studies that appear to support both sides, but most show that using glycemic index as a weight-loss strategy is not more effective than simply consuming fewer calories.
Strictly following a glycemic index table suggests choosing chocolate fudge cake (with a glycemic index of 39) over watermelon (with a GI of 72).
Proponents of GI point to studies suggesting health benefits from eating naturally low-GI foods, such as fruits, vegetables, beans and whole grains. Yet mixed messages riddle GI charts. There are numerous anomalous values on a GI table - foods that are healthy by any standard, yet have a high GI. Carrots and watermelon are examples.
When the GI first gained national attention, carrots were kicked off some menus, along with watermelon and bananas. Consumers were misled into believing these low-calorie, highly nourishing foods were fattening. For such high-fiber foods, it makes no sense to look only at GI when considering their impact on blood sugar.
One food, however, received more negative attention than any other. In fact, it presents an anomaly that strikes at the very heart of GI as a means of evaluating carbohydrates. The potato, a naturally nutrient-dense food with a long history of sustaining populations, was lumped in with highly processed foods because of its high GI. Ironically, potato chips have a low GI.
Science vs. philosophy
High-GI foods spike insulin levels and leave us hungry soon after we eat. Or so it is said. But a 1995 study tested 38 foods for their ability to satisfy hunger. Data were calculated as with glycemic index and compared to a standard - white bread - which was assigned a value of 100. A score of 150 means the food is 1.5 times as satisfying as white bread. By these standards the most satisfying food is boiled potatoes at more than 300, more than three times that of white bread, although with a similarly high GI ranking.
The study found no significant relationships between blood glucose, insulin response and satiety among the 38 foods tested. Moreover, there was a tendency for subjects to eat less food two hours after eating the high-GI foods, calling into question the very premise upon which the link between GI and obesity is founded, that low-GI foods are more sustaining. A 2003 study found that a low GI value was not associated with a slow digestion of carbohydrates.
In yet another study, reported last December, results from nearly 1,000 adult volunteers responding to a questionnaire showed no association of glycemic index, glycemic load or carbohydrate intake with insulin sensitivity and insulin secretion. However, higher fiber intake, not GI, was positively associated with insulin sensitivity, reduced body fat and a healthy insulin response.
GI came on the heels of two diet fads: the low-fat fad and the low-carb craze. Supporters of GI view it as a more balanced and reasonable approach to health. But others point out the incongruity created by forcing GI values to be predictive of weight control and health.
"GI has enjoyed increasing popularity despite the lack of research to support its efficacy as a dietary tool for weight loss, disease prevention or health promotion," says Beals. "Until large-scale studies are done using GI in a variety of circumstances and disease conditions, Americans should strive to follow the recommendations set forth in the U.S. Dietary Guidelines."
Is the appeal of GI in the science or the philosophy? Some healthy carb sources - fruits, vegetables, whole grains and beans - happen to have a low GI, and many nutrient-dense carb sources - potatoes, carrots, dried fruits and watermelon - have a high GI. Are there lessons locked in the often contradictory GI numbers? Or has the attention GI has gathered, pro and con, unveiled a serious need in the modern diet for more focus on an overall healthy eating philosophy and less attention to numbers?