Review details why many carbs aren’t ‘harmless for the heart’

I don’t make any secret of the fact that I think the low-fat/high-carb paradigm that has seemingly shaped much nutritional advice for the last few decades is not founded in good science. And variously, on this site, I’ve presented the evidence that supports this stance. Some of this research has examined the distinct lack of evidence that fats found naturally in the diet (including saturated fat) contribute to the our burden with regard to obesity and disease. Other evidence presented here, however, has highlighted that the over-consumption of carbohydrates poses very real hazards for the body and our health.

One particular condition for which the low fat/high carb principle has been vigorously applied is heart disease. The image of a fatty diet leading to fat (e.g. cholesterol) in the bloodstream which then ends up dumping itself on the inside of the arteries is one which most of us will have had in our minds at some time. For some of us, this neat little story will be quite first entrenched in our psyche, a bit like the World being round. Yet, the science does not support a strong link between supposedly artery-clogging saturated fat and heart disease, and eating less of it has been shown to be a spectacular failure in terms of reducing disease risk. The only rational conclusion one can draw from the science is that saturated fat, at worst, has a pretty benign effect on health.

Today’s blog is not so much about why low-fat is necessarily good for us: it’s about why high-carb diets can be bad, including for the heart. This post is based on some information I read yesterday to be found in a paper published last year in the journal Current Atherosclerosis Reports. This paper is essentially a summary of the science which shows that carbohydrate, particularly those releasing sugar quite rapidly into the bloodstream, can cause cardiovascular disease (CVD – essentially heart disease and stroke).

The paper starts with a discussion of the science showing that individuals who do not handle sugar all that well (for instance, those who have relatively high sugar levels after being ‘challenged’ with a standard dose of sugar) have generally higher risk of CVD over time. They also site the evidence linking poor blood sugar control with increased risk of narrowing in the arteries.

The authors of this study list a number of mechanisms through which ‘spikes’ of blood sugar might increase the risk of arterial damage and CVD. These include:

Increased ‘oxidative stress’ (free radical damage)

Increased inflammation

Protein glycation (glucose ‘bonding’ to proteins in the body and damaging them)

Increased coagulation (essentially, making the blood ‘stickier’ and more likely to clot)

They also describe some of the evidence which links diets of high glycaemic index and/or glycaemic load (see here for some discussion of these terms) and other risk factors for CVD including raised levels of bloods known as triglycerides and an inflammatory substance known as C-reactive protein.

The authors also present some evidence linking high GI/GL diets with increased CVD risk. Overall, these appear to show that:

High GI/GL diet (compared to low GI/GL diets) are associated with an increased risk of CVD of somewhere between 20 and 100 per cent.

The paper also includes a summary of the clinical research on low GI/GL diets, and in particular, their ability to induce weight loss as well as improvements in biochemical risk factors for CVD. One study cited, which I was not aware of before yesterday, concerned a substance called acarbose. Acarbose basically slows the digestion of starch, and in so doing will reduce the GI/GL of foods eaten with it. In this study, individuals were randomly assigned to take acarbose or placebo over a 3-year period [2]. During the course of the study, those taking acarbose had half the risk of developing high blood pressure or having a cardiovascular event (e.g. heart attack or stoke).

There’s a little addendum to this blog I’d like to add. I was planning to read this study on an early morning flight. However, the paper caught the eye of the two travellers to my left. Both were diabetic, and both were health professionals too. We ended up spending the whole of the 2½ flight talking about diet and health, including the nutritional management of diabetes. One of these ladies described the dietary support she’d had as ‘crap’. Having an enquiring mind, she questioned the high-carb advice given to her initially, had educated herself regarding the GI, and had subsequently stabilised her condition. Listening to this lady talk was, honestly, music to my ears.


1. Brand-Miller, et al. The Glycemic Index and Cardiovascular Disease Risk. Current Atherosclerosis Reports 2007;9:479-485

2. Chiasson J, et al. Acarbose treatment and the risk of cardiovascular disease and hypertension in patients with impaired glucose tolerance: the STOP-NIDDM trial. 2003;290:486-494

11 Responses to Review details why many carbs aren’t ‘harmless for the heart’

  1. Angie 25 April 2008 at 6:12 am #

    Did you mean ‘NOT founded in good science’ in the first sentence?

  2. J Michael Nicholls 25 April 2008 at 9:25 am #

    Surely you meant to say “I don’t make any secret of the fact that I think the low-fat/high-carb paradigm that has seemingly shaped much nutritional advice for the last few decades is NOT founded in good science.”, in your opening paragraph.

    Good posting anyhow 🙂

  3. Haarajot 25 April 2008 at 9:33 am #

    Did you forget the word ~not~ in the first sentence, or is this non-native speaker not able to read English?

  4. Peter Silverman 25 April 2008 at 10:37 am #

    I think the first sentence of this article reads the opposite of what you intended.

  5. Dr John Briffa 25 April 2008 at 11:36 am #

    THANK YOU to one and all who pointed out the typo in the 1st sentence. It’s fixed now.

  6. Mark Levin 25 April 2008 at 1:29 pm #

    “YES, the science does not support a strong link between supposedly artery-clogging saturated fat and heart disease, and eating less of it has been shown to be a spectacular failure in terms of reducing disease risk.”

    As long as we’re nitpicking your blog, the highlighted YES should probably be Yet.

    The story of how carbohydrates and particularly refined carbs contribute to heart disease is explained in detail (some would say excruciating detail) by Gary Taubes in ‘Good Calories, Bad Calories’ or ‘The Diet Delusion’ as it’s known on your side of the pond.

  7. Dr John Briffa 26 April 2008 at 12:23 am #

    Thanks Mark – ‘yet’ it is.

  8. R Vasudevan 1 August 2009 at 2:30 pm #

    The occurance of diabetes in the Indian population is far greater than anywhere else because of eating habits mostly based on rice and wheat – dehusked. The incidence of CVD is on the increase thanks to increasing consumption of refined stuff of late.
    Simple diet – we call it satwik is the best which consists of fruits, milk and the like which is devoid of meat,chillies etc – the rajas stuff and the pungent ones called the Tamas food. I suppose this is universally applicable and true.

  9. pat Halling 18 November 2011 at 8:25 pm #

    It makes you wonder why given that most people eat all the wrong things ,why is it that on balance people are living longer and longer. Is the argument if we all eat a perfect diet with perfect food that we would live even longer!! . The big killers are still with us and it looks as if they are going to be with us forever. Standing outside supermarkets with begging bowls is not going to solve the problem . It needs a concerted effort on the part of world governments to really get to grips with these diseases ,but they are too busy causing wars and wasting money and lives .


  1. Review Details Why Many Carbs Aren’t 'Harmless for the Heart' | Fitness Spotlight - 13 May 2008

    […] > Read the Full Article […]

  2. Higher overall levels of sugar in the bloodstream appears to be a good predictor of death | Dr Briffa's Blog - A Good Look at Good Health - 27 April 2011

    […] In addition, ‘spikes’ in blood sugar, can lead to other processes linked with disease including increased inflammation, increased ‘oxidative stress’ (free radical damage), and increased coagulation (making the blood ‘stickier’ and more likely to clot). You can read more about these issues here. […]

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