Medical Files
Counting the glycemic index for diabetes control
By Rafael Castillo, MD
Philippine Daily Inquirer
First Posted 01:12:00 06/07/2008
SAN FRANCISCO, California—This charming and windy city by the bay welcomed more than 13,000 medical scientists, physicians and other healthcare professionals from around the world who attended the 68th scientific sessions of the American Diabetes Association. Top scientists shared cutting-edge research, treatment recommendations and advances in controlling diabetes and preventing its long list of dreaded complications such as leg gangrene and amputation, kidney failure, heart attack and stroke.
The wanton lifestyle characterizing the past two decades has been implicated as a major cause for the alarming increase in the prevalence of diabetes worldwide. We are said to be in the fast-food era, which is fast leading us to the diabetic direction. And the Philippines is not at all spared. In 15 years the Philippines is projected to be among the top 10 countries in terms of increasing prevalence of diabetes.
Diet and increased physical activity remain the mainstay of both prevention and treatment. Being careful of what one eats is a must. Patients should be well aware of the glycemic index or GI of the carbohydrate sources they eat.
In the ’80s, Dr. David Jenkins and his colleagues at the University of Toronto researched on foods that could be recommended for people with diabetes. Prof. Jennie Brand-Miller at the University of Sydney continued the research and developed the GI.
The GI is a measure of the effects of carbohydrates on blood sugar levels. Carbohydrates that break down rapidly after eating, releasing glucose rapidly into the bloodstream, have a high GI while those that break down slowly, releasing glucose gradually into the bloodstream, have a low GI. Food items with a low GI are generally healthier for diabetics compared to those with a higher GI.
Foods with low GI have slower rates of digestion and absorption of the sugars and starches they contain. The carbohydrate or sugar load is relatively lower and less insulin is therefore required for digestion. This results in better blood sugar control. Even the lipids or cholesterol levels, particularly blood triglyceride levels, have been shown to be better controlled with more intake of low GI foods.
GI values of foods
The current validated methods of measuring GI use glucose as the reference food, giving it a GI value of 100. The GI values of other foods can be interpreted as their relative percentages on an absolute scale with sugar as the reference.
Most fruits and vegetables (except potatoes, watermelon), grainy breads, pasta, legumes/pulses, basmati rice and milk have a relatively low GI of 55 or less. Croissant, brown rice, orange, sweet potato and biscuits have a GI in the intermediate range of 55-69; and sweetened corn flakes, baked potato, white rice and white bread have relatively high GIs of 70 or more. Candies, ice creams and some cakes may have GIs approximating sugar itself.
Although diabetics should only eat low GI food items under ordinary conditions, they may need a high GI food for a more rapid rise in blood glucose levels for energy recovery after strenuous exercise and during times when they experience hypoglycemia or low blood sugar levels. Hypoglycemia may occur occasionally due to the antidiabetic drugs they take, particularly if they are on insulin.
The GI also depends on a number of factors such as the type of starch (amylose vs. amylopectin), physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal. Vinegar, for example, lowers the GI. Increased dietary fiber also slows the stomach emptying rate, thus lowering the GI. Unrefined rice or breads with higher amounts of fiber generally have a lower GI value than their refined or white counterparts.
Alcoholic intake
Aside from their fiber content, many fruits and vegetables (but not potatoes) are good for diabetics because they contain very little carbohydrate per serving, and therefore have very low GI values. Although alcoholic beverages have been reported to have low GI values, excessive amount can also have bad effects on the blood sugar levels which can drop to excessively low levels (hypoglycemia) if the diabetic has had too much to drink with too little to eat. Beer has a moderately higher GI compared to hard drinks.
Actually, if the diabetic can control his alcohol intake, small amounts of alcohol can actually help control the blood sugar level. Some studies have shown that one alcoholic drink prior to a meal reduces the GI of the meal by approximately 15 percent. The problem however is that most individuals cannot stop after the first alcohol drink.
Research over the last 10 years has shown that individuals who adhered to a low GI diet developed less diabetes and heart disease on the long term. Postprandial or after-meal increases in the blood sugar levels—so-called glycemic "spikes" following a meal—may injure the blood vessels of all body organs due to increased oxidation partly induced by increased insulin levels.
Think GI
This is the reason blood sugar levels in diabetics and nondiabetics should be checked on a fasting state (before breakfast) and two hours after starting to eat a regular meal (postprandial blood sugar). Even if the fasting blood sugar (FBS) level is normal, complications can subsequently develop if the postprandial blood sugar levels are elevated. Hence, postprandial hyperglycemia is now considered a major risk factor for atherosclerosis or the narrowing of the blood vessels.
Most medical organizations concerned with diabetes control support the use of the glycemic index or GI in recommending dietary prescriptions for diabetics and those with tendencies to develop diabetes. So the next time you order two scoops of your favorite ice cream, think GI!
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