Low Glycemic Index Diets


Examples: South Beach Diet®, Nutri-system®, Sugar-Busters®.  The glycemic index was developed in the 1980's as a way to distinguish "good" carbs from "bad carbs" by measuring how fast they enter the bloodstream. Learn about this index and whether it can help your weight and health.

STRATEGY: All carbohydrates eaten should have a low glycemic index

All kinds of foods are allowed, but foods high in refined carbohydrates are very limited.


All kinds of foods are allowed (psychologically reassuring)
May improve appetite control
May improve blood sugar control
May make it easier to lose weight
May reduce risk for chronic diseases
Metabolism does not slow down as much as with low-cal and low-fat diets


Glycemic index concept is complicated and hard to learn.

Glycemic load is also important and confusing for many people (see below).

Individual metabolisms vary, so the glycemic index of a food can be very different from one person to another.

A low-GI diet allows all kinds of foods, including processed and artificial foods, and therefore may not be that much healthier than the Standard American Diet (SAD). Low GI diets do allow unhealthy refined carbohydrates, as long as they are in a low glycemic index form.  Fortunately, this means that these diets are much lower in refined carbohydrate than standard diets.  However, because many starchy foods have a low glycemic index (such as whole grains and legumes), a low-GI diet is not necessarily a low-carbohydrate diet, therefore carbohydrate-sensitive people  may have difficulty losing weight on this diet, especially as they get older.

Low glycemic index diets represent a significant improvement over standard (low-calorie and low-fat) weight loss diets, because they take into consideration the quality of the carbohydrates in the diet and how those carbohydrates are metabolized.

What is the glycemic index?

The glycemic index, or “GI”, is a measure of how a food affects your blood glucose level after you eat it. By definition, 50 grams (1.7 ounces) of pure glucose, which is the simple sugar found in our bloodstream, has a glycemic index of 100, and all other foods are compared to that standard. There are no foods that have a higher glycemic index than pure glucose. So, a food that has a glycemic index of 50 raises blood sugar 50% as much as pure glucose dose. A food that has a glycemic index of 30, only raises blood sugar 30% as much as pure glucose does.  So, lower numbers mean a slower and/or lower rise in blood sugar.

All kinds of things affect the glycemic index of a food, including how much protein, fiber, and fat it contains, since all of those ingredients slow down the absorption of the carbohydrates into the bloodstream.

When laboratories determine the glycemic index of a food, they have 10 people fast overnight, give them each a test food (like white potato) the next morning, then measure their blood glucose over the next 2 hours to see how it rises. Then they take the average of the 10 measurements, compare it to glucose, and publish that as the glycemic index of white potato.  They have to take an average, because the glycemic index of a food varies from one person to another, depending on each person’s unique metabolism.  So, keep in mind that your own blood sugar response to white potato may be quite different from the published number, since the scientists did not test your individual reactions to these foods.

  • Foods with a GI of less than 55 are considered “low glycemic index” foods.
  • Foods with a GI of between 55 and 70 are considered “medium” GI foods.
  • Foods with a GI of more than 70 are considered “high” GI foods

What is glycemic load?

The glycemic index (GI) measures how much your blood sugar rises if you eat 50 grams of a particular type of carbohydrate.  However, it doesn’t tell you how much your blood sugar rises if you eat 10 grams, or 1,000 grams of that food. The glycemic index varies depending on how much of a food you eat, whereas the “glycemic load” (GL) takes the amount you eat into consideration.

[glycemic index X grams of carbohydrate eaten] ÷ 100 = glycemic load

So, if you want to know the glycemic load of your baked potato, you multiply the GI of baked white potato, which is 85, times the number of grams of carbohydrate in your baked potato (an average baked potato contains about 34 grams of carbohydrate):

[85 x 34] ÷ 100 = Glycemic Load of 28.9

Why does the glycemic index matter?

A sharp rise in blood glucose will trigger a sharp rise in insulin, the hormone that tells your body to make fat. If you’re trying to lose fat, that’s the last thing you want. So, if you eat foods that cause softer peaks in blood sugar, you may also soften your insulin spikes–which means you may store less carbohydrate as fat.

The vast majority of carbohydrate-containing foods our hunter-gatherer ancestors would have encountered would have had a low glycemic index (whole fruits and vegetables); therefore our bodies are probably better adapted to handle these slow carbohydrates, compared to the rapidly-digested, concentrated, processed, refined carbohydrates that are so prevalent in our diet today, such as sugar and flour.

There are lots of other reasons why smoothing out the blood sugar-insulin roller coaster can be helpful—for example, you may feel less hungry, less irritable, and less tired. Your cholesterol profile, blood pressure, and triglycerides may improve. And your risk for developing chronic diseases, such as diabetes, heart disease, and cancer, may be lower (see: carbohydrates).

Low glycemic index diets are metabolically superior to standard low-calorie and low-fat diets.  When you are trying to lose weight with those standard diet plans, your body tends to fight back by slowing down your metabolism, making it progressively harder to lose weight. Low GI diets tend to slow metabolism less than high GI diets, making it easier to lose weight.  This was shown in a 2012 study by Dr. David Ludwig (to read an abstract of this study, click on the link below:



Overall, a low glycemic index diet is significantly healthier, more comfortable, and more effective than standard low-fat and low-calorie diets for most people.  Low carbohydrate diets are even better for weight loss than low glycemic index diets, but may be harder for some people to follow.

For more information about the glycemic index, you may be interested in The University of Sydney’s excellent website at www.glycemicindex.com.

For more information about Dr. David Ludwig’s research on low glycemic index diets and the treatment of childhood obesity, visit his site at www.endingthefoodfight.com.

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Last Modified: Sep 3, 2015