Glycemic gobbledygook

The concept of glycemic index is meant to help determine what foods raise blood sugar a lot vs. what foods raise blood sugar a little. Dr. Jennie Brand-Miller's searchable database can be found here.

I have to admit that glycemic index provided me with a sense of false assurance for some years. It screwed up my health until I came to understand the issues a lot better.

For those of you just starting out in nutritional conversations, glycemic index (GI) represents a comparison of the blood glucose area-under-the-curve (AUC) over 2 hours after consuming 50 grams of the food in question compared to the AUC of glucose or white bread. Volunteers involved in developing these values are healthy people who are generally of normal weight.

Glucose, by definition, has a GI of 100. An equal quantity of sucrose (50% glucose, 50% fructose) has a GI of 60, lower than glucose. An equal quantity of whole wheat bread has a GI of 68-77 (Yes: The GI of whole wheat is higher than sucrose). Non-carbohydrate foods, such as eggs or avocado, have no GI since they do not impact on blood glucose.

Because the GI is also sensitive to how much carbohydrate is contained, the concept of Glycemic Load (GL) was introduced:

GL = (GI x amount of carbohydrate) / 100

GL is therefore the GI that incorporates the glycemic potential of the food of interest. GI does not vary with portion size; GL varies with portion size.

Let's take whole wheat pasta, a food regarded by most people as a healthy choice. Whole wheat pasta has a GI of 55--fairly low--and a GL of 29. A serving of 180 g (approximately 6 oz cooked) provides 50 g carbohydrates.

People who advocate that low-glycemic index foods would say that this is a desirable profile and should therefore replace high-glycemic index foods.

I say WRONG. First of all, most of us are not slender 20-somethings. We will therefore not show the same response as a young, slender person (like the GI volunteers), but will show exagerrated blood sugar responses. So this much low-glyemic index whole wheat pasta will typically yield a blood sugar of 120-200 mg/dl in non-diabetic people, high enough to trigger glycation. Sure, a high-glycemic index food, such as white flour birthday cake with plenty of sugary icing, might trigger a blood sugar of 140-250 mg/dl, much worse. But that doesn't make the lower blood sugar following pasta any less bad--it's still terrible.

Another issue: GI is assessed over a 2-hour timeline. What if blood sugar remains high in a sustained way, say, over 6 hours? That's precisely what whole wheat pasta will do: Keep blood sugar high for an extended period.

So not only does a low-glycemic index food like pasta increase blood sugar in most of us extravagantly, it does so in a sustained way.

Lastly, low-glycemic index pasta still triggers small LDL particles to an extreme degree, as I discussed in the previous Heart Scan Blog post, Small LDL: Complex vs. simple carbohydrates.

Don't be false reassured by the notion of low GI or GL. In fact, I'd go so far as to say that NO glycemic index is a GOOD glycemic index (or load). The foods we want to dominate our diet are the foods that aren't even listed in the GI database.

Comments (14) -

  • Santiago

    5/12/2010 11:12:07 PM |

    I've seen many posts like this, but all of them seem a bit ambiguous about whether small LDL is related to BG spikes or an independent effect of carbohidrates.
    Say, someone that eats that 180g of pasta but BG stays under 100 will still produce tons of small LDL?

  • Anna

    5/12/2010 11:55:06 PM |


  • Michael Barker

    5/13/2010 1:32:59 AM |

    My big problem with GI or GL was fructose. It does not raise blood sugar but it does attack the liver.

  • Matt Stone

    5/13/2010 2:44:16 AM |

    If 6 measly ounces of whole wheat pasta sends your blood sugar over 120, much less to 200, you're probably seriously ill. But you talk about it like it's impossible to lower blood glucose levels to a set number of carbohydrates. That's not true at all. It's easy actually, and there's so much more complexity to this overall issue that posts like these are aggravating. I've even gotten to the point where I could eat double that glycemic load without my blood sugar spiking above 75.

  • Darrin

    5/13/2010 3:22:07 AM |

    Yeah, GI and GL are best for diabetics and others with strong insulin resistance. Although I agree that foods without GI values should be the basis of our diets (meats, most vegetables), if you have strong insulin sensitivity you'll probably be just fine with some roots, dairy, fruit, and nuts.

  • 2012

    5/13/2010 3:29:50 AM |

    perfect one.

  • Lance

    5/13/2010 12:51:59 PM |

    Several points:

    Isn't there a pretty big difference between raising your blood sugar to 120 mg/dl after a meal, as opposed to 200?

    The American Association of Clinical Endoctrinologists suggests an upper limit of 140 mg/dl two-hour postprandial blood glucose.  The International Diabetes Federation has the same figure.

    In contrast, 200 is usually considered a symptom of full-blown diabetes.  So it would really seem to depend on which figure we are talking about.

    I personally find the glycemic load a helpful piece of data.    Almost all fruits and vegetables have some kind of glycemic load.   Spinach, for example, consists of 56% carbohydrate, 14% fat, and 30% protein.  But a 10 oz. bag only has a glycemic load of 4, vs. 14 for  piece of white bread.  (Granted, you're only getting 65 calories of energy from all that spinach.)

    Regarding whole wheat pasta: perhaps different websites give different glycemic load values. gives a value of 16 for a full cup of cooked whole wheat elbow noodles, vs. the 29 you quoted.

    I find it helpful to know I can cut the glycemic load of that pasta from 16 to 8 just by eating a half-cup instead of a cup (though in fact I rarely eat pasta at all.)  The glycemic load deals with real effects of quantifiable portions of food, and as such is an interesting piece of the puzzle. But, as you have wisely pointed out many times, checking your own blood sugar is the best way to understand what is really going on...with you.

  • KENNY10021

    5/13/2010 1:06:55 PM |

    Yes it will still produce tons of small LDL.....two different issues.....carbohydrate effect LDL particle size tremendously....I can attest to this first hand......while the high BG levels have a whole host of other bad effects related to damaging cells at the core and thus disease ramifications, insulin issues, etc.

  • Ned Kock

    5/13/2010 2:44:17 PM |

    Hi Dr. Davis.

    It is worth noting that there is a huge gap between glycemic loads of refined and unrefined carbohydrate-rich foods:

  • homertobias

    5/13/2010 2:59:57 PM |

    Very nicely said.  I mean it.  Maybe I'll use it in my practice.

  • Dr. William Davis

    5/13/2010 9:24:43 PM |

    Hi, Lance--

    I understand your concerns. However, I am less concerned with what the "official" organizations tell us is normal or abnormal, and more concerned with levels in which glycation develops.

    Glycation develops in a continuous fashion with blood glucose: The higher it is, the more glycation results . . . starting in the "normal" range fasting and postprandial.

  • DrStrange

    5/14/2010 1:37:11 AM |

    5/15/10  6:35 p.m. PDT

    Matt Stone, just went to your website and got attacked by Malware.

  • Apra -- The Shaman

    5/14/2010 6:47:57 PM |

    "I've even gotten to the point where I could eat double that glycemic load without my blood sugar spiking above 75."

    There's a guy in India who claims he can live on nothing but air too.

  • jpatti

    7/2/2010 2:14:40 PM |

    The reasons sucrose has such a "good" GI is cause it's half fructose.  Fructose doesn't convert to glucose so doesn't raise bg.  It is cleared from the blood by the liver which converts it to triglycerides.  So it raises serum triglycerides at least for a while.  It eventually gets cleared from the blood by adipose.

    Bread, potatoes, other starchy foods... starch is long chains of glucose, so it raises bg.  But if you have a normal system and can handle bg, you burn it as fuel instead of having fat floating in your blood until it gets deposited around your belly.  So for those without bg problems, the worse GI foods are better for health!  

    for those who DO have bg issues, the GI and GL are useless.  You don't care what happens to some average group of people, but what happens to YOUR bg.  This is what is useful whether you have diabetes or not: