High carb diets are bad news for the blood vessels

Cardiovascular conditions such as heart disease and stroke are a major cause of disability and death. For years we’ve been led to believe that fat is the major dietary offender here, but in reality the science shows that naturally occurring fats are not the issue. In fact, some fats (principally so-called omega-3 fats) actually help protect against these conditions.

The other side of this, of course, is that when it comes to cardiovascular disease, carbohydrates are far from blameless. Certain carbohydrates, principally those that are most disruptive for sugar and insulin levels, are strongly associated with an increased risk of cardiovascular disease. See here and here for more about this.

One way to measure the impact of diet on risk of cardiovascular disease risk is to see what effect it has on blood ‘markers’ such as blood fat, glucose and insulin levels. Another way is to assess the impact diet has on the function of the arteries in the body. The standard way to measure this is assess what is known as ‘flow mediated dilatation’ (FMD) in the brachial artery (a major artery in the arm). This measurement essentially tests the ability of arteries to relax, which is something that is good for blood flow in the artery, and is associated with a reduced risk of cardiovascular disease risk. Reduced FMD is a sign of reduced health in the artery, and is a potential risk factor for heart attacks and stroke.

In a recent study, 40 overweight and obese adults were put on one or two diets for a period of 12 weeks. One of the diets was low fat, the other was carbohydrate restricted. Both diets provided the same number of total calories (1500 cals per day). FMD was measured at the beginning and end of the study.

In the low-fat diet eating group, FMD decreased over the course of the study.

In the carb-restricted group, it increased.

In the carb-restricted groups, levels of insulin unhealthy blood fats called triglycerides also fell significantly.

This study is reminiscent of a study I reported on here [2]. In this study, overweight and obese men were fed with one of four test meals, after which FMD was assessed 2 hours later [2]. The four text meals were water (placebo), glucose (high GI), cornflakes (high GI) and bran flakes (low GI). Compared to the placebo, FMD was reduced after all of these meals, but only to a statistically significant degree after the two high GI meals.

Taken together, the results of these two studies suggest that a carbohydrate-rich diet, particularly if those carbohydrates are disruptive to blood sugar levels, is bad news for the health of the blood vessels.


1. Volek JS, et al. Effects of dietary carbohydrate restriction vs low-fat diet on flow-mediated dilation. Metabolism. 2009 Jul 24. [Epub ahead of print]

2. Lavi T, et al. The Acute Effect of Various Glycemic Index Dietary Carbohydrates on Endothelial Function in Nondiabetic Overweight and Obese Subjects J Am Coll Cardiol 2009;53:2283-2287

6 Responses to High carb diets are bad news for the blood vessels

  1. Ted Hutchinson 31 July 2009 at 12:25 pm #

    Another route to reducing triglycerides and improving vasular function is to INCREASE omega 3 intake and DECREASE (to about 4% of calories) omega 6 intake.
    Association of serum n26 and n23 polyunsaturated fatty acids with
    lipids in 3 populations of middle-aged men

    It’s inevitable that if people are cutting back on calories from carbohydrate intake that they will make up for those lost calories by increasing fat consumption.
    It would be a mistake to increase industrial vegetable oils such as corn, soybean, safflower and sunflower oil, or anything that contains them. This includes most processed foods, especially mayonnaise, grocery store salad dressings, and fried foods.

    Olive oil and coconut oil are good alternatives as well as butter and some sources of locally rendered lard.

  2. Ted Hutchinson 31 July 2009 at 5:08 pm #

    Something about the software garbled the above research title
    It should have read
    serum omega 6 and omega 3 polyunsaturated fatty acids.

  3. Haide Villuendas 31 July 2009 at 7:00 pm #

    I wonder what are the implications of the recent study on high carbohydrate diets for long distance runners who are advised to eat carbohydrates to compensate for the energy loss?

  4. Barrie 1 August 2009 at 12:15 pm #

    I have been using beef dripping as fat in some foods. Would anyone be able to give me an indication if this is better than vegetable oils

  5. Trinkwasser 11 August 2009 at 11:36 pm #

    Another interesting paper by Jeff Volek looks at the effect of low carbing on other less often measured cardiovascular risk factors


    IME Mark Sisson


    is an excellent source of information about athletic performance while low carbing, and on fats. My experience – without the excess carbs I turn saturated fats into HDL rather than LDL. How did you know I was just eating rump steak???

  6. Paul Rogers 13 November 2009 at 2:25 am #

    With all due respect, you’re cherry picking.

    The weight of evidence is more the reverse. Just a few examples:

    Phillips SA, Jurva JW, Syed AQ, et al. Benefit of low-fat over low-carbohydrate diet on endothelial health in obesity. Hypertension. 2008 Feb;51(2):376-82.

    Shimabukuro M, Chinen I, Higa N, et al. Effects of
    dietary composition on postprandial endothelial function and adiponectin concentrations in healthy humans: a crossover controlled study. Am J Clin Nutr. 2007 Oct;86(4):923-8.

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