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Low Carb Diets: Doing More Harm Than Good?

Monday, December 07, 2009 Posted by Peter Janiszewski, PhD

An intriguing editorial published recently in the prestigious New England Journal of Medicine suggests that low-carb diets may not be all they’re cut out to be, and in fact may be more dangerous than the “deadly” Western diet.

Given that I grew up in a Polish household (albeit not always in Poland), I know a little bit about having a high-carbohydrate diet. In fact, in most eastern European homes, it is not uncommon to have sliced bread (buttered, of course) with every meal of the day. Also, a dinner short of potatoes is simply not dinner. Since moving out on my own almost 10 years ago, my diet has changed considerably – a change that becomes most evident when I politely decline to ingest all the bread, potatoes, cakes, pastries that I am offered when I visit my folks (without fail, my mom is always offended by such a gesture). Adopting a diet low(er) in carbohydrates was not necessarily an intentional move, but sort of just happened. Slowly, I started cutting back on the obvious excesses of sweets, gummy candies, chips, pop, and most recently my beloved pretzels. I also cut back on my intake of white pasta (a staple of the undergraduate student), white bread, and to be honest, rarely eat potatoes or French fries outside of my parent’s home. Now, I find that if I consume too much carbohydrate, I simply don’t feel good. Thus, I have been living on a fairly low carb diet for a while now, and would often remind my parents (based on things I had read or heard) that a diet high in carbs is not ideal.

Well, I should have known better; mom is always right…

Dr. Steven Smith, the author of the editorial, suggests that the low-carb diet, despite being in the spot-light for quite some time is nothing more than a fad diet, something he eloquently describes as “a bright flash that quickly fades, only to be followed by another best-seller and a new face on the talk-show circuit.”

The crux of Smith’s criticism of the low-carb diet rests on the results of a recent paper by Foo and colleagues which investigated the effects of different diets on the formation of atherosclerotic plaques (fat build-up in the arteries) in mice.

In the study, 3 groups of mice were each fed different diets and monitored over time: 1) regular diet (low fat, moderate protein, high carbohydrate – think Polish diet), 2) Western diet (high fat, moderate protein, moderate carbohydrate), or 3) high fat, high protein, but low carbohydrate diet.

The surprising finding of this study was that the mice fed the low-carb diet had developed twice the atherosclerotic plaque formations as compared to the mice on the Western diet (typically thought of as “atherosclerotic” diet).

The interesting thing here is that despite the significant difference in the progression of vascular disease in the mice on the low-carb diet – their metabolic profile (levels of blood cholesterol, for example) was indistinguishable from that of the mice on the Western diet. This suggests that factors other than those commonly measured in clinic may explain how a low-carb diet may be so atherogenic (plaque forming).

The two suggested candidates are an increased level of free fatty acids in the blood (released from insulin resistant fat cells and implicated in the initiation of inflammatory processes) or a reduced level of circulating endothelial progenitor cells (produced in bone marrow and help maintain the health of the blood vessels).

The key argument made by Smith is that we have previously looked only at “classical” risk factors (cholesterol, glucose, insulin) for cardiovascular disease when investigating the effect of various diets on health. In fact, some studies have shown that low-carb diets may reduce levels of blood cholesterol in the short-term. However, as well stated by the author, the low-carb diet “might increase the risk of cardiovascular disease through mechanisms that have nothing to do with these "usual suspects" and so provides a note of caution against reliance on the traditional cardiovascular risk factors as a gauge of safety.”

While more research on low-carb diets needs to be conducted in humans, for the time being, it may be a good idea to avoid jumping on the low-carb bandwagon.

In the end, my mom may have been right all along, and Dr. Atkins (originator of the low-carb craze) had it all wrong.


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Smith SR (2009). A look at the low-carbohydrate diet. The New England journal of medicine, 361 (23), 2286-8 PMID: 19955530

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12 Response to "Low Carb Diets: Doing More Harm Than Good?"

  1. Kate Porter Said,

    I don't have an NEJM subscription, so haven't read the article. However, a few things pop out at me as potential red flags.

    1. This is based on a study in mice, being fed (presumably) processed mouse food. People are not mice, and we do not eat processed pellet food. While I recognize that animal models have an important place in health research, it sounds incredibly premature to me to extrapolate from one mouse study to make a blanket statement about a very large human diet range. However, this isn't my main concern. My main concern is

    2. There's carbs, and then there's carbs. The traditional "low-carb" diet--i.e., the one that the diet industry refers to--typically means low in starch (potatoes, flour, etc) and high in protein and vegetables. However, vegetables are almost entirely carbs; they're just not starch carbs. If you look at total carbohydrate, a diet high in fruits, vegetables, and whole grains is very high-carb, as is a diet of white bread, potatoes, and gummy bears. But clearly the fruit/veggie diet is a lot healthier than the white bread/gummy bear diet. Which of those two high-carb diets corresponds to the "high-carb" diet the mice were on? There's really no way to make that kind of comparison. Similarly, a diet of red meat, bacon, and eggs is high in protein, as is a diet with a lot of beans, tofu, and egg whites--but they're not equivalently healthy.

    A diet low in processed carbs, but high in fruits & veggies, would not be low-carb but would probably be a lot healthier than a "low-carb" diet that is mostly meat and fat. In the sense that the "low-carb diet" craze--i.e., Atkins, etc--is probably doing more harm than good, sure, no argument from me there. But I don't think it's valid to extrapolate from that to say that we should all eat lots and lots of "western" carbs (i.e., white flour and sugar).

    Posted on December 7, 2009 at 11:40 AM

  2. Yoni Freedhoff Said,

    Hi Peter,

    Slightly odd to base one's atherogenic conclusions on a mouse study as they don't always translate to people.

    While I'm by no means a low-carber (my issue with it is its non-sustainability for the vast majority of those trying it), data, also from NEJM in humans suggest that in fact its metabolic profile is superior with higher HDL and improved insulin sensitivity.

    Will have a more careful read of the study but I wonder if this isn't a premature editorial?


    Posted on December 7, 2009 at 2:26 PM

  3. Beth Said,

    I don't have a subscription either, so am eager for someone like one of the Drs. Eades or Stephan Guyenet or Kurt Harris gets a hold of this study and report.

    I'm not a LC fanatic (I'm going for more of a moderate/paleo carbs approach myself), so tend to agree with Kate that food quality is also key. Our industrial diet is really a disaster whether you eat fat or carbs.

    Posted on December 7, 2009 at 3:35 PM

  4. Peter Janiszewski, PhD (Cand.), MSc Said,

    @ Kate Porter - Excellent comments Kate!

    Regarding the use of mice - of course we need to see human studies to see if the same pans out in free-living humans. Part of the advantage of using mice is really the other side of the cirticism you pose - if you want to test effects of certain diets on an outcome - mice are much better subjects than humans to study such a question. Mice could only eat the diet they were given - humans can vary their diet tremendously from day to day, thus don't make ideal subjects for such studies. Again, it is true that we need human studies but basic science has its strength in removing some of the countless confounders inherent to human studies. My research is in humans, and when it comes time to analyse my data - I am always a bit envious of basic scientists who have so much more control of the environment of their subjects (I can only co-vary for so many variables in my analysis:)

    @ Yoni Thanks for the comment! I hope you got my email with a PDF of the article. As you probably know - dietary macronutrient composition and health is not my direct area of research, so when I read the editorial I was quite intrigued - especially given that NEJM thought it worthy enough to publish and the fact it was written by a prominent scientist in the area - Steven Smith of Pennigton Biomedical Center.

    Is the editorial premature? Maybe. As I stated in the post, the whole crux of the argument rests on the results of this one animal study.

    The interesting thing Smith alludes to is the fact that common CVD risk factors may not be the right targets by which to judge the safety of a given diet, etc. The notion that the CVD risk status between the two groups of mice was identical and yet the plaque formation significantly greater in the low-carb group suggests other factors are at play other than the usual suspects. Thus, it is possible that the same studies that showed an improvement in the classical CVD risk factors in response to low-carb diet - those subjects may have had increased atherosclerotic plaque formation, but of course the variable was not measured.

    All of this is simply speculation. I await a human study that assesses the effects of different diets on coronary calcium or some advanced marker of CVD risk other than the intermediate metabolic risk factors.

    Posted on December 7, 2009 at 4:08 PM

  5. Jan Said,

    I found it typical. Not only do mice translate unpredictable to men. They even translate unpredictable to other strain of mice.

    Although the NEJM is a prestigious journal with a stellar impactfactor, but they do tend to be biased. I can recall the rejection of the Lyon Heart study that showed lifesaving properties of canola oil without lowering cholesterol. The editor wrote that could not be true.

    The authors did publish the study (JAMA), but they had to change the title into 'Mediterrean diet'. I know the Americans aren't to strong in geography and somehow are bothered that canada is a neighbor, but this one gets beyond wildly creative.

    Really don't want to offend your mom, but hold your horses (for a while)

    Posted on December 7, 2009 at 4:52 PM

  6. GnomeX Said,

    Supplement of the study with more detail on diets (took me awhile to realize this was here, doh):

    Eades attack:

    Great post from hyperlipid:

    Posted on December 7, 2009 at 5:35 PM

  7. Peter Janiszewski, PhD (Cand.), MSc Said,

    @ Jan - Thanks, Jan - you've just guaranteed me a spiteful extra serving of mashed potatoes with my holiday dinner from my VERY offended mom :)

    (Obviously kidding)

    Thanks for your comment!

    Posted on December 7, 2009 at 5:41 PM

  8. Beth Said,

    In a bit of serendipity, Jenny on Diabetes Update has posted her frustration with rodent research and chronic disease. And in the comments, Steve Parker shared this on the study mentioned in the NEJM editorial:

    The December 3 issue of New England Journal of Medicine has an article - "A Look at the Low-Carb Diet" - that sounded interesting and educational.

    Turns out it's simply about research done in mice. Not just your average mouse either, but a strain deficient in apolipoprotein E, which are particularly susceptible to atherosclerosis when fed a high-fat
    Western diet.

    The whole point seems to have been to cast aspersions on high-fat low-carb diets eaten by humans. To scare us into thinking that WE'LL develop atherosclerosis.

    Here's the link to Jenny's post:

    Posted on December 7, 2009 at 7:42 PM

  9. Travis Saunders Said,

    @ Beth,

    Thanks for the links! This has certainly generated some lively discussion, I hope people continue to weigh in with their thoughts on the article!


    Posted on December 7, 2009 at 10:04 PM

  10. Peter Janiszewski, PhD (Cand.), MSc Said,

    @ GnomeX Thanks very much for the great links. I hadn't realized the original study had drawn so much criticism. Seems interesting that NEJM would now publish an editorial so heavily based on the paper.


    Posted on December 7, 2009 at 10:32 PM

  11. Anonymous Said,

    the article says "high fat, high protein, low carb".
    Maybe the problem is the high fat. Is it not possible to have a high protein, low carb diet with low to moderate fat? Could this change the outcome?

    Posted on December 15, 2009 at 12:13 PM

  12. speedwell Said,

    I can either follow a low-carb diet, or I can go back on the two type-2 diabetes medications my very impressed doctor cancelled, and gain back the fifty pounds I lost (without exercising more than the occasional longish walk) over the past six months.

    My brother, who was diagnosed with fasting blood sugars of almost 300 (almost twice what I was) and peripheral neuropathy in his feet, normalizes his blood sugar purely through exercising after a moderately-low-carb dinner. The wretch eats bread. His foot problems are gone. How much exercise did the mice get?

    Posted on December 19, 2009 at 6:02 AM


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We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.


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