Glycemic Index of Carbohydrates

There has been much conversation over the years about carbohydrates. As our population started to put on more and more weight some people even suggested that carbs were the problems. If people would eat fewer carbs it would result in weight loss. That isn't the case. Your body must have carbohydrates to burn for energy.  

Not too long ago it was assumed carbs could be broken into two groups, simple and complex carbs. Complex are better for you than simple based on how long it takes to digest them. Even though there is a degree of truth there, the reasoning is based on incorrect assumptions. And how specific carbs are categorized is not correct based on the glycemic index.

About 20 years ago, a research scientist,  David J. A. Jenkins, M.D., Ph.D., D.Sc from the University of Toronto, decided to test the complex carbohydrate theory. In 1981, he used glucose, blood sugar, as the constant to compare other carbs to. From this he developed the glycemic index. Simply he did clinical tests where people consumed different carbs and then he tested their blood to determine how fast the carb was digested and hit the blood stream. The faster it was in the blood, the higher the glycemic index of that particular food. 

What are High Glycemic Index Carbs?

High-Glycemic Index foods are quickly digested and absorbed, producing a rapid rise in blood sugar and resulting in high insulin levels. Low-GI foods, on the other hand, are slowly digested and absorbed, producing a smaller, more gradual rise in blood sugar and much lower insulin levels. Why is this important? High levels of blood sugar and insulin have been linked to many of the health problems that are so common today.

The GI of a food is influenced by a variety of factors including the degree to which a food is processed; how long the food is cooked; the kind of starch, sugar, or fiber the food contains; and the foods acidity. In general, anything that speeds the rate at which a food is digested and absorbed will raise its glycemic index.

Foods that rank high on the glycemic index include products made from finely ground flours like bread and baked goods; processed breakfast cereals; snack foods like chips and pretzels; baked, mashed, and French fried potatoes; and short-grain (sticky) rice. Foods that rank lower on the glycemic index include most vegetables and fruits; sweet potatoes; legumes; minimally processed whole grains such as thick-cut oatmeal, oat bran, long-grain brown rice, barley, and bulgur wheat; pasta; and dairy products.(1)

The glycemic index tells you how quickly a carbohydrate-containing food turns into sugar, but it doesn’t tell you how much carbohydrate is in a serving of a food. To assess the full impact of a food on blood sugar levels you should have an idea of both. This is where glycemic load comes in.

The Glycemic Load

Glycemic load is a relatively new term that considers both the glycemic index and the amount of carbohydrate in a food. The carbohydrate in carrots has a high GI. But carrots are pretty low in carbohydrates compared to other foods like potatoes, bread, and sweets, so glycemic load of carrots is relatively low. The bottom line is  if a food has a high GI but very little carbohydrate, it will not have much impact on blood sugar and insulin levels. On the other hand, if a food has both a high GI and a high carbohydrate content, consumption should be limited or avoided.

Side note: If you are diabetic, you probably already know this information. You should have learned this in the classes. So what we are saying here is ALL of us should be on the diabetic diet. And if you aren't on it now, you likely will be when your body becomes insulin resistant and you develop diabetes. Or you will crash and burn.

Since we are talking about diabetes, let's briefly add a little more information: 

Adult On Set Diabetes:

Why am I mentioning diabetes here?

There is a direct relationship between consumption of high glycemic foods and developing insulin resistance. Diabetes is caused by insulin resistance.

It is important for all of us to understand the glycemic index of foods we eat. You must eat carbs for energy but eat the right ones. Read here about Diabetes, a different perspective on preventing and curing it.

Who can Benefit from Eating Low on the Glycemic Index?
By helping to maintain lower blood sugar and insulin levels, a low-GI diet may be useful in preventing and treating a variety of the health problems. Here are some examples of how eating low on the glycemic index can help promote excellent health:

Diabetes - Substituting low-GI carbohydrates (like thick-cut oats, pasta, and legumes) for high-GI carbohydrates (like processed cereals, white bread, and potatoes) can help lower blood glucose levels in people with diabetes. This is why the GI has been an integral part of medical nutrition therapy for diabetes in Australia, New Zealand, Canada, and Europe for many years.

A low-GI diet may also help prevent diabetes from ever developing in the first place. Harvard University researchers who tracked the eating habits of over 100,000 men and women found that people whose diets are low in fiber and high in refined and high-GI carbohydrates are more than twice as likely to develop type 2 diabetes, as are people who eat a fiber-rich diet with a low glycemic load.

Cancer - Insulin is a cellular growth factor. Many studies have shown an association between high insulin levels and a variety of cancers including breast, colorectal, prostate, and pancreas. Other studies have shown links between diets high in sugar, refined carbohydrates, glycemic load, and cancer. This suggests that lifestyle changes like maintaining a healthy body weight, exercising, and eating a healthy low-GI diet may help protect against cancer at least partly by lowering insulin levels.

Cardiovascular disease - As with type 2 diabetes, researchers have found that a diet high in refined and high-GI carbohydrates may substantially raise the risk for heart disease. These foods increase blood insulin levels, which in turn contribute to a higher blood pressure, higher levels of blood fats (triglycerides), lower levels of HDL (good) cholesterol, and an increased tendency for dangerous clots to form and linger in the blood.

Hypoglycemia - People who have meal-related reactive hypoglycemia secrete too much insulin after eating. This causes the cells to remove so much sugar from the blood that they feel weak, shaky, irritable, headachy, unable to concentrate, and very hungry with a few hours of eating. Choosing low-GI carbohydrates can help prevent this type of hypoglycemia because eating foods that promote a gradual rise in blood sugar and a lower insulin response reduces the likelihood that blood sugar levels will drop too low.

Obesity - Since low-GI foods are slowly digested, they provide a gradual and sustained rise in blood sugar. This keeps you feeling full and satisfied and delays the return of hunger between meals. Conversely, high-GI carbohydrates provide short bursts of energy that satisfy you in the short term but soon leave you hungry. Many of the fat-free and low-fat foods that have become popular over the last decade—such as bagels, processed cereals, rice cakes, crackers, snack chips, and cookies—tend to rank high on the glycemic index and may actually contribute to a pattern of overeating in some people. (see the section on Obesity and weight loss here for more information on this process and why most people can't lose weight without addressing insulin resistance.)

Polycystic Ovary Syndrome (PCOS) - This disorder affects about 7 percent of reproductive age women. Symptoms include altered hormone levels, disturbances in the menstrual cycle, infertility, and acne. Because PCOS is often associated with insulin resistance, women with this disorder are at increased risk for developing diabetes, high blood pressure, and heart disease. Measures that improve insulin sensitivity, such as weight loss and exercise can help reverse PCOS symptoms. A low-GI diet, which minimizes insulin secretion, may also confer benefits.

Athletic Performance - Low glycemic index carbohydrates should be chosen for pre-competition meals and snacks. These slowly digested carbs provide a steady stream of glucose to working muscles during exercise and enhance performance by making glycogen stores last longer.

When high-GI foods are eaten just prior to a "sports" competition they can actually impair performance because they stimulate more insulin, which speeds removal of glucose from the blood and can lead to hypoglycemia. On the other hand, high-GI carbs are the preferred choice after the event because the insulin surge helps replenish muscle glycogen stores.

(The above chart of people who can benefit from low glycemic carbs it taken from Sandra Woodruff. Her book is an excellent source of information and meals using low glycemic foods.(1)

Footnotes:

(1) Sandra Woodruff, MS, RD, LD/N is author of "The Good Carb Cookbook: Secrets of Eating Low on the Glycemic Index"

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