Is glycemic index irrelevant?

University of Toronto nutrition scientist, Dr. David Jenkins, was the first to quantify the phenomenon of "glycemic index," describing how much blood sugar increased over 90 minutes compared to glucose. The graph is from their 1981 study, The glycemic index of foods: a physiologic basis for carbohydrate exchange. The research originated with an effort to characterize carbohydrates for diabetics to gain better control over blood sugar.

Since Dr. Jenkins’ original work, thousands of clinical studies have been performed by others exploring this concept. The food industry has also devoted plenty of effort exploiting it (e.g., low-glycemic index noodles, low-glycemic index cereals, etc.).

Most Americans are now familiar with the concept of glycemic index. You likely know that table sugar has a high glycemic index (60), increasing blood sugar to a similar degree as white bread (glycemic index 71). Oatmeal (slow-cooked) has a lower glycemic index (48), since it increases blood sugar less than white bread.

A number of studies have shown that when low glycemic index foods replace high glycemic index foods (e.g., whole wheat bread in place of cupcakes), people are healthier: less diabetes, less heart attack, less high blood pressure. Books have been written about glycemic index, touting its benefits for health and weight control. Health-conscious people will try to substitute low-glycemic index foods for high-glycemic index foods.

So what’s not to like here?

There are several fundamental flaws with the notion that low-glycemic index foods are good for you:

1) Check your blood sugar after a low-glycemic index food like oatmeal. Most non-diabetic adults will show blood sugars in the 140 to 200 mg/dl range. The more central (visceral) fat you have, the higher the value will be. In other words, an apparently “healthy” whole grain food like oatmeal can generate extravagantly high blood sugars. Repeated high blood sugars of 125 mg/dl or greater after eating increase heart disease risk by 50%.

2) Foods like whole wheat pasta have a low glycemic index because the blood sugar effect over the usual 90 minutes is increased to a lesser degree. The problem is that it remains increased for an extended period of up to several hours. In other words, the blood sugar-increasing effect of pasta, even whole grain, is long and sustained.

3) Low-glycemic index foods trigger other abnormalities, such as small LDL particles, triglycerides, and c-reactive protein (a measure of inflammation). While they are not as bad as high-glycemic index foods, they are still quite potent triggers.

Low-glycemic index foods trigger the very same responses as high-glycemic index foods—they’re just less bad. But less bad does not equate to good. Low-glycemic index foods cause weight gain, trigger appetite, increase blood pressure, and lead to the patterns that cause heart disease.

High-glycemic index foods are bad for you. This includes foods made with white flour (bagels, white bread, pretzels). Low-glycemic foods (whole grain bread, whole wheat crackers, whole wheat pasta) are less bad for you—but they are not necessarily good.

Don’t be falsely reassured by foods because they are billed as “low-glycemic index.” View low-glycemic index foods as indulgences, something you might have once in a while, since a slice of whole grain bread is really not that different from a icing-covered cupcake.

Comments (20) -

  • W8liftinmom

    2/16/2010 12:24:18 AM |

    If high GI foods are bad and low GI foods are just less bad, then what does that leave that is good?  Protein and fat?  Sounds good to me!

  • Health Test Dummy

    2/16/2010 12:35:35 AM |

    I absolutely love this post!

    So many people don't understand this basic concept.

    I have had to expose several 'health conscious' individuals at various health food stores as to WHY that Agave Nectar is just nature's 'High Fructose Corn Syrup'. Along with the Ethanol poisoning from the Fructose, their insulin is spike through the roof for longer than if they just ate table sugar!

    Thank you for continuing to educate the masses on the truth, instead of these horrific 'wives tales' that just don't seem to die!

  • mongander

    2/16/2010 2:37:32 AM |

    I was diagnosed a type 2 diabetic 30 years ago.  Now at age 70, I've lost 60 pounds through exercise and avoiding processed foods.  My breakfast every morning is boiled oats-groats and whole barley.  My vision is 20/20 and my A1C is always under 6%.  My diet is mostly vegetarian except for salmon or mackerel in my salad.  I usually avoid wheat products except when travelling or on social occasions.

  • Dr. William Davis

    2/16/2010 3:55:06 AM |

    Health Test: I love the "agave nectar is just nature's 'high-fructose corn syrup.'" Well said!

  • Anonymous

    2/16/2010 6:28:06 AM |

    What about Stevia? is stevia ok as a sugar substitute? please advise.

  • Alan

    2/16/2010 12:07:35 PM |

    I don't disagree with your comments on GI in general, although as an Aussie I believe  it should be noted that Jennie Brand-Miller had a great deal to do with the develpment of the GI/GL concept.

    As a type 2 diabetic I used the concept in a slightly different way. I used peak post-prandial testing to develop my own personal database of the effect of various foods on my own blood glucose levwels. In effect, a personal GL list.

    My main reason for commenting was this: "Check your blood sugar after a low-glycemic index food like oatmeal. Most non-diabetic adults will show blood sugars in the 140 to 200 mg/dl range." Although I agree that oatmeal would do that to me - probably worse than 11mmol/L(200mg/dL) I have doubts that it would do that to a non-diabetic. In my experience testing friends and relatives I have never tested anyone who had levels that high after a meal who was not subsequently diagnosed as a type 2. The non-diabetics I have tested, regardless of the carb load of the meal (usually a feast like Christmas) have never reached 8(144), let alone higher numbers.

    I would be interested to know if you have seen numbers like that personally in your clinical experience in non-diabetics, apart from those affected by medications like Prednisone. Or was the statement based on the experience of others?

    This is one of the few published examples that I am aware of showing post-prandial blood glucose levels in non-diabetics:

    Note particularly slides 17 and 27.

    Cheers, Alan

  • Peter

    2/16/2010 12:30:38 PM |

    Why do you think the traditional extremely high carb Japanese diet
    left its population almost free of obesity and diabetes?

  • Renfrew

    2/16/2010 12:37:19 PM |

    Good post.
    In the last few years there has been a better parameter, called "Glycemic load" (GL).
    While GI is always the same, independent of HOW MUCH you eat, GL takes into account "portion size".
    This is important because if you are eating half an apple or 2 apples it will have the same GI regardless, but not the same GL.  


  • Anonymous

    2/16/2010 12:44:11 PM |

    Asians eat lots of rice, and they're skinny. Therefore starch is good for you and should be consumed in large quantities. Buy my ebook, "The Edgy Contrarian Hipster Diet"!

  • Anonymous

    2/16/2010 12:58:53 PM |

    The Mercola mixed diet recommends eating occasional higher glycemic foods AFTER the rest of a meal...since this apparently blunts the insulin response.

    I've been indulging in oatmeal...eaten dry as a snack.  Also fruit.  Shame on me.

    Also beans as part of meals...not recommended (like wheat as far the effect on the gut?).  Not to mention the salted nuts roasted in hydrogenated oils.

    Still have some work to do.....

    I buy food only every 3 weeks or so...and I find that when I run out of "favorites" near the end of this period and am eating only lean meats...assorted veggies...olive oil...spices...I feel better.  Though I do seem to get a major itch to go buy some "junk food" a kind of panic as far as running out of food.  

    Wondering WHY this is...since I do feel I have addictions?  Need to go to a clinic to recover? Wink

    I may be addicted to the sugar rush???  The oatmeal rush? The bean rush?  The hydrogenated oil/nut rush?  

    Dependent on my food reactions?

  • Tony

    2/16/2010 1:18:46 PM |

    Hi Dr. Davis,

    If I remember correctly, in your book you recommend oat bran to decrease cholesterol.  Is that still the case?  (Many thanks for all the great work.)

  • Anonymous

    2/16/2010 2:31:46 PM |

    Thank you so much for this -- the proof is always in the testing and I abandoned many "low-GI" foods early on.  

    It sounds good, but ... I never had any success with it.  I thought it must be ME, and ended up feeling (more) sorry for myself.

  • Jeff

    2/16/2010 3:15:04 PM |

    "A slice of whole grain bread is really not that different from a icing-covered cupcake," except for the fiber, micronutrients, antioxidants, etc.

  • Dr. William Davis

    2/16/2010 4:06:46 PM |


    Yes, I've seen many, many people with either "normal" (<100 mg/dl or 5.5 mmol/L) or slightly increased blood glucose (100-110 mg/dl or 5.5-6.0 mmol/L) with high postprandial glucoses.


    I believe there are a number of reasons, including the use of rice in place of wheat. Being part Japanese, I am well aware of their eating habits which are not as high-carb as often made out. There are confounding factors, as well, including iodine content of the diet.

    Also, there are indeed fat, diabetic Japanese people, also. Diabetes is, in fact, a growing problem in Japan.

  • whatsonthemenu

    2/16/2010 7:17:14 PM |

    Dr. Davis is right about the Japanese diet.  Northeast Asians eat a bowl of rice or noodles at every meal, but that is the only high GI food at the table.  A typical Japanese, Korean, or Chinese meal includes fish or meat and non-starch vegetables.

    Moreover, type II diabetes is common among middle-aged Asians, who get the disease at lower BMIs than non-Asians.  

    I am wondering about the accuracy of identifying whole grain products as low GI.  The Easy GL Diet Handbook lists a GI of 37 for whole wheat pasta compared to 43 for regular pasta.  Likewise, brown rice and long-grain white rice have nearly identical GIs of 55 and 56, respectively.  Low GI is defined at around 55 or less, so pasta qualifies as low GI, but the difference between whole grain and refined varieties is not significant, especially when GI is converted to GL.  As the good doctor notes, it's best to avoid grains altogether.

  • Anonymous

    2/17/2010 4:11:16 AM |

    I did the test today
    And this are the results I had.

    After wake up: 86

    A bit over an hour after breakfast (rise with some vegetables, one egg, broccoli, and one cup of lapsang tea): 93

    30 Minutes after lunch (Portion of papaya, bowl of 'auyama' soup, half chicken breast with tomatoes and green peas, one boiled potato and salad with olive oil, one cup of lapsang tea): 111

    60 Minutes after lunch: 101

    Afternoon before eating some oats: 94

    30 Minutes after oats (quaker classics, soaked in water for 10 minutes with some almonds): 110

    60 Minutes after oats: 121

    30 Minutes after dinner (3/4 chicken breast same sauce as lunch, broccoli, salad, couple glasses of red wine): 109

    60 Minutes after dinner: 116

    90 Minutes after dinner: 92

    This opens many questions to me, like how much the time at which I had the oats affects. Or the fat I just had them with some almonds instead than as part of a whole meal

    Also as dinner seems to have more effect on my glucose than lunch even when lunch had  fruit and a potato I wonder if this is due to the black tea at lunch or to the time of the day.

    Also I wonder how much effect had the wine at dinner.

    I'll do some more tests when my fingers recover

  • Jonathan

    2/18/2010 9:35:22 AM |

    I would add to this post the fact that fructose has low GI, yet is more toxic and screws up the metabolism more than most other carbohydrates.  (E.g. causing fatty liver disease and insulin/leptin resistance; increasing hunger rather than satiating it.)  Food companies are motivated to add fructose to their products so they can claim a lower GI (hence the agave craze), but the fructose does more harm than most higher-GI carbs.

  • renegadediabetic

    2/18/2010 2:36:37 PM |

    I soon discovered that "low GI" foods, like oatmeal and other whole grains, still cause an unacceptable rise in my blood sugar.  Low GI may be a little better than high GI, but filtered cigarettes are a little better than non-filtered cigarettes.  Both are still bad.

    Glycemic load, which also takes into accout the number of carb grams, is much more relevant.  Non starchy veg, meat, & fat are about as low GI/GL as you can get.

    As for agave nectar, they still have to process it to extract it.  I'm not sure it's all that "natural."

  • buy jeans

    11/3/2010 3:13:22 PM |

    Low-glycemic index foods trigger the very same responses as high-glycemic index foods—they’re just less bad. But less bad does not equate to good. Low-glycemic index foods cause weight gain, trigger appetite, increase blood pressure, and lead to the patterns that cause heart disease.

  • Ivan

    7/2/2011 3:56:20 PM |

    I eat oats with milk and 2 tbsp of ground flax seeds every morning, and since I'm doing that every morning I lost 10 pounds, and I feel great. I don't crave for sweet anymore. So, I don't understand how low glycemic foods like oats can increase your weight?
    Few of my friends who implemented oats and flax seed in their diet had similar results.
    No one mentioned very valuable fiber that oats contain.

    Male, 37 y.o.