Skip to main content

What's the Glycemic Index?

What's the Glycemic Index?

Find out the not-so-simple truth behind high-GI foods and what role they play in your diet.

Despite how little the average American knows about proper nutrition and healthy eating, almost anyone can tell you two facts:

  1. Brown rice is better than white rice
  2. Too much sugar will give you diabetes

    But does anyone really understand why these statements are true? And just how true are they? …Enter glycemic index…

In case you are unfamiliar with the term, any South Beach or fad diet enthusiast can tell you that the glycemic index (GI) is a way to measure a food’s effect on the body’s blood sugar levels. Why is this important? Quick science lesson! Basically, when carbohydrates are absorbed and digested from the foods you eat, they are broken down into smaller glucose molecules, which serve as the primary fuel for your muscles and brain. This raises glucose (aka sugar) levels in the blood, which stimulates your pancreas to secrete insulin. Insulin's primary function is to lower glucose levels, and the amount of insulin released by the pancreas is dependent on how much glucose is in the blood. After a carb-heavy meal, glucose levels can become especially elevated, causing an insulin overload in the body. As a result, your blood sugar levels drop below normal due to this spike in insulin (this is the energy “crash” you feel after consuming huge amounts of diet soda or the like.) Your body will recognize that blood sugar levels are low, and will activate hormones that stimulate hunger. So, even if you had ice cream and a giant plate of spaghetti at lunch, your brain will trick you into thinking you need even more. And we all know what happens when we consume calories in excess…not desirable!

So, advocates of fad diets and weight-loss miracles will use the science behind GI to tell you that eating low-GI foods will increase weight loss, decrease risk for diabetes, and decrease your risk for heart disease. For all you athletes, you may also hear that eating low-GI foods before a workout can increase muscle endurance. But what does the research say?

In the most recent review of the scientific literature, an article from the International Journal of Sports Nutrition indicated that though the topic has been researched for over 15 years, the connection between low-GI foods and increased endurance remains unclear. Though many articles have found associations between high-GI foods following exercise and glucose re-synthesis, more recent studies have found conflicting results. So unfortunately, a low-GI diet is only recommended on a case-by-case basis.

The effects of low-GI foods on weight loss are inconclusive as well. Though dieters will tout the benefits of increased satiety from consumption of low-GI carbohydrates, research has shown low-GI, high-carb diets to be equally as effective as low-fat, high-GI diets. Basically, when it comes to weight loss, calorie control conquers all!

On the flip side, research around the impact of a low-glycemic diet on diabetes and heart disease is more promising. Diets that are consistently high in carbohydrates can cause blood sugar fluctuations that decrease insulin sensitivity over time. Numerous studies have found links between low-GI diets and increased levels of HDL cholesterol (the good stuff!), improved lipid profile, and reduced levels of C-reactive protein (present with inflammation, which can lead to atherosclerosis.) Several more recent studies have also found associations between high-GI diets and risks for several cancers, including colon, breast, and prostate.

So, even if the health benefits are not totally conclusive, it seems sufficient to say that following a low-GI diet could be conducive to better health in the long-term. But how do you know which foods to choose? Like I mentioned before, the glycemic index is simply a way to score an individual food’s effect on blood sugar levels. If a food has a higher GI score, it is more prone to raising levels of glucose in the blood. Foods are categorized by the following ranges:

Low glycemic index foods: 55 or less
Medium glycemic index foods: 56-69
High glycemic index foods: 70 or higher

Here is a sample of the glycemic indexes of some common foods, including bread, milk, and juice:

As a general rule of thumb, low glycemic index foods are typically whole grains, fruits, and vegetables. Processed and canned foods generally have higher glycemic indexes, and grains that are finely ground (like flour), are usually higher than grains that are intact (like brown rice). Also, “above ground” vegetables, like broccoli or peppers generally have lower GIs than “below ground” vegetables, like carrots, yams, or potatoes.

A few other things to keep in mind:

  • The glycemic index of a food has nothing to do with the nutrient content, so please don’t cut out any foods based solely on glycemic index, you will be missing out on valuable vitamins, minerals, and phytochemicals!
  • You may have to consume unrealistic amounts of certain high-GI foods to see any impact on blood sugar levels. Carrots have comparatively high GIs, but unless you are eating them by the bushel, you won’t notice much of a change in blood sugar.
  • The glycemic index only accounts for foods eaten singularly, rather than in combination. Other elements of a meal will affect blood sugar levels, including fiber content (more fiber can control blood sugar), and preparation methods

In conclusion, glycemic index is not the be-all end-all. External factors such as exercise, stress, and individual variations can affect blood sugar levels almost as much as the foods we consume. Since most low-GI foods are whole grains, fruits, and vegetables, I say, go nuts! But don’t exnay the carrots or green peas, please.

19 / 09 / 2017 1R