Another dietary myth debunked: Low-glycemic index carbohydrate diet

“The unexpected findings of the study suggest that the concept of glycemic index is less important than previously thought.”

The media release is below.

Low-glycemic index carbohydrate diet does not improve CV risk factors, insulin resistance

In a study that included overweight and obese participants, those with diets with low glycemic index of dietary carbohydrate did not have improvements in insulin sensitivity, lipid levels, or systolic blood pressure, according to a study in the December 17 issue of JAMA.

Foods that have similar carbohydrate content can differ in the amount they raise blood glucose, a property called the glycemic index. Even though some nutrition policies advocate consumption of low-glycemic index foods and even promote food labeling with glycemic index values, the independent benefits of glycemic index, and its effect on risk factors for cardiovascular disease and diabetes, are not well understood, according to background information in the article.

Frank M. Sacks, M.D., of Brigham and Women’s Hospital and Harvard Medical School, Boston, and colleagues conducted a trial in which 163 overweight adults with prehypertension or stage 1 hypertension were given 4 different complete diets that contained all of their meals, snacks, and calorie-containing beverages, each for 5 weeks; and completed at least 2 study diets. The four diets were (1) a high-glycemic index (65 percent on the glucose scale), high-carbohydrate diet (58 percent energy); (2) a low-glycemic index (40 percent), high-carbohydrate diet; (3) a high-glycemic index, low-carbohydrate diet (40 percent energy); and (4) a low-glycemic index, low-carbohydrate diet. Each diet was based on a healthful Dietary Approaches to Stop Hypertension (DASH)-type diet, which is rich in fruits, vegetables, and low-fat dairy foods, and low in saturated and total fat.

The researchers found that at high dietary carbohydrate content, the low- compared with high-glycemic index level decreased insulin sensitivity; increased low-density lipoprotein (LDL) cholesterol; and did not affect levels of high-density lipoprotein (HDL) cholesterol, triglycerides, or blood pressure. At low carbohydrate content, the low- compared with high-glycemic index level did not affect the outcomes except for decreasing triglycerides. In the primary diet contrast, the low-glycemic index, low-carbohydrate diet, compared with the high-glycemic index, high-carbohydrate diet, did not affect insulin sensitivity, systolic blood pressure, LDL cholesterol, or HDL cholesterol but did lower triglycerides.

“In the context of an overall DASH-type diet, using glycemic index to select specific foods may not improve cardiovascular risk factors or insulin resistance,” the authors conclude.

(doi:10.1001/jama.2014.16658; Available pre-embargo to the media at http://media.jamanetwork.com)

Editor’s Note: Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.

TV Note – This week’s JAMA Report video is on the effect of a high- vs low-glycemic index carbohydrate diet on cardiovascular risk and insulin resistance. The video, along with embedded and downloadable video, audio files, text, documents and related links will be available at 3 p.m. CT Tuesday, December 16 at this link.

Editorial: Role of Glycemic Index in the Context of an Overall Heart-Healthy Diet

Robert H. Eckel, M.D., of the University of Colorado Anschutz Medical Campus, Aurora, writes in an accompanying editorial that many of the results of this study were contrary to what had been expected.

“When glycemic index was lower in the high­ carbohydrate diet, insulin sensitivity not only did not increase but decreased. With the same diet pattern, levels of LDL cholesterol and apolipoprotein B (a secondary end point) increased, with no changes in HDL cholesterol or triglyceride level or blood pressure.”

“The unexpected findings of the study by Sacks et al suggest that the concept of glycemic index is less important than previously thought, especially in the context of an overall healthy diet, as tested in this study. These findings should therefore direct attention back to the importance of maintaining an overall heart-healthy lifestyle, including diet pattern.”

(doi:10.1001/jama.2014.15338; Available pre-embargo to the media at http://media.jamanetwork.com)

Editor’s Note: The author has completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

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6 thoughts on “Another dietary myth debunked: Low-glycemic index carbohydrate diet”

  1. Always good to know that things that don’t matter (glycemic index) have no effect on other things that don’t matter (so called “risk factors”).

  2. My read of this is that all of the diets used in this study are low fat. Low fat is being called into question; see The Big Fat Lie by Nina Teicholz.

  3. ““The unexpected findings of the study by Sacks et al suggest that the concept of glycemic index is less important than previously thought, especially in the context of an overall healthy diet, as tested in this study.”

    It was never important in the context of an overall healthy diet. That it is “less important” is hardly shocking.

    Glycemic index is relevant to people concerned with blood sugar levels. Blood sugar levels, not part of “an overall healthy diet.” Whatever the heck that is.

  4. This is just bad science and no conclusions should be drawn.

    From the script of the Video in the JAMA network (the link from the article):

    “TURNS OUT THIS MEAL OF CHICKEN AND SAUCE OVER PASTA, COOKED A LITTLE LESS, WHICH MAKES IT A LOWER GLYCEMIC FOOD, HAD THE SAME EFFECT AS THIS CHICKEN AND SAUCE MEAL COOKED WITH INSTANT WHITE RICE, WHICH IS A HIGHER GLYCEMIC FOOD.”

    i.e. they say that chicken w/ pasta is a low-glycemic meal and the same chicken w/ rice is high-glycemic meal (there are pics in the video of the dishes)…..and with such minute changes and after no more than few weeks they saw no major changes except lower TG – this seems not surprising to me.
    From personal experience, real low-carb/low-glycemic diet dramatically lowers TG, BP and weight – but the difference must be significant and not the difference between white pasta and white rice.
    When changes are as dramatic – no bad “large studies” are required a simple observation is enough. Large studies are required to show negligible effects. This is just bad science.

  5. I vote more junk science. My junk contribution: Low carb diets are obviously good for weight loss, weight loss is good for Type II. XXL to XL and two inches down in pant size in under a year in my case. My A1C went from 8 to 5.5 – no exercise as I have significant muscle atrophy and use a power chair. Blood pressure from border line to normal. All the index did was help me choose which foods to avoid to keep my blood sugar from spiking. The experts just can’t let go of their misunderstand of low carb/paleo diets IMO. It appears their solutions have lead to an epidemic of Type II and obesity so I can understand why they are defensive. Dr Atkins was right all along.

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