September 26, 2007

EASD: Why the OGTT Fails to Predict Heart Attack and Why this Harms People

Diabetes in Control reported today on a study presented at EASD by Dr Esther van 't Riet which found that in normal people the A1c is predictive of non-fatal heart attack, but, both fasting bg and the 2 hour OGTT [Oral Glucose Tolerance Test] results are not.

Before you conclude that this study "proves" that post-meal spikes are not what cause heart attacks, it is worth considering how the OGTT works and why it does NOT mimic the way your body responds to high carb meals.

The OGTT involves sucking down 70-75 grams of pure glucose and then testing blood sugar at various intervals to see what happens. It is a convention of medical research to use the OGTT value to diagnose "Impaired glucose tolerance" when the 2 hour result is over 140 mg/dl (7.7 mmol/L) and to diagnose diabetes when the 2 hour result is over 200 mg/dl (11.1 mmol/L).

However, glucose is the one form of sugar that does not require any digestion. It goes directly into the bloodstream within 15 minutes, unlike starch or sucrose which must be broken down in the stomach and may take up to an hour to reach the blood.

So the 75 grams of glucose you swill during an OGTT hit the blood in 15 minutes. In most people with the kinds of blood sugar control likely to result in a 5.5% A1c (the level Dr. Riet's study showed to correlate with heart attack)this initial very high blood sugar spike provokes reactive hypoglyecmia.

So what typically happens is that the person with marginal blood sugar control--the 5.5% A1c that marks a higher risk of heart attack--will get a very high blood sugar reading at 1 hour only to have the blood sugar plummet in the second hour. it is quite possible to have a normal or even a low blood sugar two hours after taking an OGTT where the one hour value was over 200 mg/dl (11.1 mmol/L). But this study only looked at that second hour response in diagnosing "impaired glucose tolerance."

However, look what happens when these same people with the 5.5% A1cs and "normal" two hour OGTT values eat the same number of grams of carbohydrate that are used in the OGTT in the form of real food.

That hamburger bun and order of fries with the 75 grams of carbohydrate digest more slowly, thanks to the carbohydrate they contain being combined with fat and protein. So if you have an A1c of 5.5% and test your blood sugar after eating 75 grams of carb in real food you are more likely to see something like 180 mg/dl (10 mmol/L) at one hour after eating and 160 (8.9 mmol/L) at two hours. By 3 hours your blood sugar may have dropped to 120 mg/dl, but until it does you have spend a couple hours with blood sugar levels that are known to be high enough to damage the organs!

It is a shame that almost no medical authorities test people for meal tolerance rather than using pure glucose syrup for the OGTT. The meal tolerance test, where a meal containing real food with a known carb count is served and blood sugar measured at one and two hours, would give doctors a much better idea of what is happening in the patient's body day in and day out. It would also be very likely to show a very tight correlation between exposure to elevated blood sugars after meals and increased incidence of heart attack.

Instead, the researchers here, who clearly have NEVER MEASURED THEIR OWN BLOOD SUGARS and do not understand that a "normal" two hour results on an OGTT may not indicate normal blood sugar response to meals day in and day out, look at that 2 hour OGTT results and conclude that, since the OGTT results don't correlate with heart attack incidence, blood sugar is not causing heart attack. Instead they hypothesize that the A1c is only "a marker" and elevated blood sugars is NOT the cause of heart disease.

This is tragic. Because lowering blood sugar after meals is probably the single most powerful tool available to us to avoid heart disease!

But sadly, the researchers in this case conclude that doctors should not attempt to lower A1c but should just keep treating cardiac risk factors with expensive drugs.

I am sure you will hear doctors citing this study as a reason to avoid testing after meals or reducing blood sugar spikes since "clearly" the study shows that spikes don't correlate with heart disease.

But those of us who do control our blood sugar and avoid post-meal blood sugar spikes know that controlling spikes so that they don't go over 140 mg/dl (7.7 mmol/L) lowers blood pressure, lowers triglycerides and LDL and raises HDL without the need for expensive drugs. Which suggests that elevated post-meal blood sugars are what raise the risk factors and that normalizing blood sugar could prevent heart disease.

Sadly, bad science in the form of over-reliance on the OGTT will keep most people from ever learning this.


Anonymous said...

"So what typically happens is that the person with marginal blood sugar control--the 5.5% A1c that marks a higher risk of heart attack--will get a very high blood sugar reading at 1 hour only to have the blood sugar plummet in the second hour. it is quite possible to have a normal or even a low blood sugar two hours after taking an OGTT where the one hour value was over 200 mg/dl (11.1 mmol/L)."

This is *exactly* what happened to me for years, resulting in leaving the doctor's office being told there's absolutely nothing wrong with me (my two-hour lows were always under 60).

Now, of course, I know that it's insulin resistance, and I know what to do about it - but I can't help feeling like I'd like those ten or so years of my life back when I was told I was "perfectly normal" but felt sick all the time and passed out from low blood sugar occasionally after all those high-carb, low-fat meals. Sigh.

Jenny said...

Chez Shoes (love the shoes!),

It's never too late to get back in control. And you can reverse almost all of the early damage caused by high blood sugars.

I had a very similar situation except that I actually tested "pre-diabetic" in my 20s but doctors told me that because I was thin it "was nothing" and to ignore it. I was eating the old "healthy whole grains" hippie diet full of rice and fruit. Sigh, indeed.

Lili said...

What? They only looked at the two hour number? I've heard that the spike is usually at one hour until you're diabetic, when it changes to two hours, and that was certainly true for me.

Jenny said...


By the ADA's definition, Impaired glucose tolerance is defined by a 2 hour OGTT result over 140 mg/dl.

Anything under that is treated as "normal." It is only now that we are getting the continuous glucose monitor studies that we are starting to have some understanding of what normal is.

But because for almost 30 years they have been using that 2 hour value for diagnosis researchers keep using it to keep their results consistent with earlier studies.

As a result, we get a lot of data that is confusing--like this study since most of us don't start to get high 2 hour numbers until many years after we are getting diabetic readings at 1 hour.

paul said...

I think you are slightly misunderstanding the researchers. They do say they think that HbA1C is probably a marker (as you say) but in the same sentence they say that they think glucose is probably a mediator. Also this page makes their position clear
"The clinical meaning of this is that, even in subjects without diabetes, it is very important to maintain optimal glycemic control," van 't Riet told heartwire.

I would agree that when they say that other things (statins etc) give bigger bang-for-the-buck for heart disease, it seems like unsupported musings, not science.

Anna said...


Have you had a chance to pick up a copy of GAry Taubes' new book, Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Nutrition, and Disease? It's on bookshelves now. It's right up your alley!

I'm thinking about sending a copy to both my primary care doctor as well as my endocrinologist.
Taubes is an award winning free-lance journalist with post graduate training in science, so his book is not just another diet book. He thoroughly examines what the science does and does not say about the roles of diet, nutrition, and disease. I'm hoping it is a catalyst for some major changes.

Jenny said...


I plan to read the Taubes book. I'm familiar with his "what if it's all been a big fat lie" article.

Unknown said...

I'm going through this right now, I went to the doctor, feeling I have insulin resistence. I'm clocking my sugar readings from 120 up to 170 2 hours after eating carb meals. I'm pretty careful about not eating high empty sugar.

My doctor runs an A1C, not a OGTT, or even a fasting sugar which isn't going to show one way or another about the insulin resistence. (it was 5.7 up .1 from last time).

I loved your site, I'm working on this week keeping carbs under 30 per meal 100/day then going to re-test my levels to see if they come down.

The attitude from doctors that "oh you are in the normal range", when in reality you are not and can be at risk for heart disease and more just is almost criminal. I'm trying so hard to lose weight, and watching every calorie and carb I eat, exercising and the weight isn't coming off. I'll just keep lowering the carbs until I see results, since this is all I can do right now.