The Glycemic Index
How would you like to have a handy reference that could improve your health and help prevent things like diabetes and heart disease? Hey, you say, that’s great! How much does it cost? Well, it’s free and out there for anyone to use. It’s called the glycemic index and it’s a simple tool that can help you stay healthy.
What it is ...
The glycemic index, also called GI, is a list of foods that contain carbohydrates. What makes it different from your grocery list is that it ranks how those carbohydrates affect your blood sugar levels. Current research suggests that stable blood sugar levels benefit health, and that frequent irregularities in blood sugar levels may contribute to maladies like diabetes and heart disease.
The GI was created by analyzing, over time, the blood of healthy volunteers after they had ingested a variety of carbohydrates. Then, using a scale from 0 to 100, with 100 representing simple sugar, those foods were listed in the index according to how they affected the blood sugar levels of the volunteers. Highly processed foods like white bread and starchy food like potatoes earned a high number while foods such as whole grains, unsweetened yogurt and apples earned a low number, thus the terms high-glycemic and low-glycemic. Foods that rank at 70 or higher are high GI, while foods ranked below 55 are low GI. There is also a mid-range from 56 to 69 that includes syrups, pomegranate juice, muesli and some breads.
The glycemic index of a certain food also takes into account its type of sugar or starch, the amount of protein, fiber and fat that it contains, how highly processed it is, the way it has been cooked, cooking time, its acid content and ripeness. There are several different GI scales and testing methodologies available, some with differing values for the same food. For further information on the glycemic index itself, a comprehensive, searchable database is available online, maintained by the University of Sydney in Australia.
...and why it's important
Simply put, high-glycemic foods cause "spikes" — a rapid rise and fall — in blood sugar and insulin levels because the body digests and absorbs them so quickly. These episodes have been linked to greater sensations of hunger and higher stress hormone levels. Experts believe that diets filled with high GI foods may lead to overeating, obesity and adult onset diabetes.
By contrast, low-glycemic foods take much longer to digest, providing the body with a slow, steady supply of energy that prolongs a feeling of fullness and helps prevent overeating, promotes healthy cholesterol levels and decreases the risk of diabetes.
If used intelligently as part of a broader balanced diet, the glycemic index is a good general reference for choosing healthy food. Some of the benefits gleaned from eating low-glycemic foods and maintaining stable blood sugar levels include:
- Weight control
- An increase in insulin sensitivity
- A lower risk of heart disease
- Healthy blood cholesterol levels
- An increase in satiety
- Improved physical endurance
- Faster recovery from exercise
What It's Not
The glycemic index is not a cure-all for diabetes or other diseases, nor should it be used as the sole reference for a balanced diet, since it applies to only one aspect of nutrition — carbohydrates.
Our bodies require three types of nutrients: carbohydrates, fats and proteins. Of the three, carbohydrates are the major source of energy in the diet, providing us with the immediate fuel we need to solve a math problem, climb the stairs or run a marathon. Carbohydrates are broken down into simple sugars by the body, transported in the blood, and then moved into the cells with the help of insulin.
The glycemic index does not measure fats or proteins and both of those nutrients affect your body's response to carbohydrates when eaten in combination. For example, eating a high-glycemic food like white bread will spike your blood sugar, but eating it with a protein like chicken or a fat like olive oil will reduce its effect on blood sugar levels. In addition, other factors such as serving size, an individual's insulin resistance, even the time of day, can affect how your body responds to a particular carbohydrate.
Even though the GI is a useful tool, it’s not a complete one. Two notable examples illustrate its shortcomings. Carrots have a comparatively high GI value, despite being a nutrient-rich and healthful food. But because the amount of carbohydrate consumed from a serving of carrots is quite small, the net glycemic load is not so great. Conversely, fructose (as in the high fructose corn syrup commonly found in soda) has a lower GI value due to the way it is metabolized, despite being nutrient-poor. So, just because a food has a low GI value doesn't mean it's good for you.
How to use it
Common sense use of the glycemic index is as simple as replacing highly processed grains and sugars with whole grains, vegetables and fruit — and avoiding high GI foods by themselves. Soft drinks and other sweetened beverages are particularly notorious in this regard. Try substituting soft drinks with sparkling water or unsweetened tea to avoid those nasty spikes in blood sugar.
Remember, eating fats and proteins along with carbohydrates in a balanced meal will alter your body's response to those carbohydrates, but that’s not an excuse to have French fries with every meal. Rather, it’s an incentive to choose low GI value foods when feasible to promote long term health. And, you should not avoid vegetables like corn, potatoes or squash simply because they have a high GI value, but enjoy them in moderation in a balanced meal that includes healthy fats and protein. As a general rule, combining protein with carbohydrates promotes healthy blood sugar levels. Some examples of healthy combinations of this sort are:
- A bagel with cream cheese and smoked salmon or with peanut butter
- Yogurt or nuts with breakfast cereal to add some protein and balance the glycemic index
- Potatoes in a stew or with an omelet, not alone as a snack (like potato chips)
Cooking methods and serving temperatures also affect the GI value of foods. Pasta, for example, should always be cooked and eaten al dente or "firm to the teeth," since overcooking will raise its GI value in addition to reducing its texture and flavor. Though a processed food, al dente pasta has a low GI value due to a unique bonding of the carbohydrate with gluten, making it more difficult to digest. Potatoes have a lower GI when boiled rather than baked, and when served cold, as in potato salad. Acidifying the meal with lemon juice or vinaigrette also lowers its GI value. And sourdough bread has a lower GI value than yeasted breads.
Low GI Foods
Low GI foods are the least processed foods. Here are some examples:
- All non-starchy vegetables including spinach, onions and broccoli
- Temperate fruits, such as berries, cherries, apples and pears
- Nuts, seeds and legumes
- Unsweetened yogurt and cheese
- Whole grains that are minimally processed, preferably with the whole kernel, such as steel cut oats, brown Basmati rice, dense whole grain breads with nuts, seeds or sprouted grains, sourdough bread, lightly sweetened granola or muesli and al dente pasta
- White flour and whole wheat flour have similar high glycemic index values. For this reason, when eating whole wheat bread, make sure that the bread you choose contains whole grains or kernel for an optimal GI value.
High GI Foods
High GI foods are the most highly processed foods. Here are some examples:
- Refined flours and grains
- Refined sweeteners
- Low-fiber breakfast cereals
- Sweetened beverages, including soft drinks and juice
- Tropical and dried fruits
- Starchy vegetables such as potatoes, squash and corn
Beyond the GI
In the struggle to maintain healthy blood sugar levels, there are other tools in the health toolbox besides the glycemic index. Here are some other ways you can promote blood sugar stability:
- Cut hydrogenated or partially hydrogenated oils from your diet completely. The trans fats found in hydrogenated oils have been shown to interfere with insulin secretion and increase blood sugar levels.
- Be sure to eat enough fish or take fish oil supplements.
- Chromium and magnesium are vital for the body to properly maintain healthy blood sugar levels. Consider supplementing if dietary levels are not sufficient.
- Try to eat adequate meals throughout the day, and then minimize snacking or eating between meals. If you do snack, use the principles of the glycemic index to make good choices, such as a handful of nuts or some plain yogurt with fruit instead of potato chips or pretzels.
- Eat plenty of fiber, especially soluble fiber.
- Cinnamon and prickly pear cactus purportedly help regulate blood sugar.
- Maintain your muscle mass.
Finally, on a more celebratory note, recent research shows that a glass of wine or beer during or before meals helps to keep blood sugar levels healthy. Bon appétit!