Thursday, June 28, 2012

What Reading That Low-Carb Gives You Heart Disease Paper Actually Told Me

Low-Carb Version of MyPlate Designed by Low-Carb Conversation's Mindy Noxon Iannotti
The short version is that it told me that in this case the British Medical Journal, and possibly the authors and this study's peer reviewers, value the publication of unsubstantiated alarmist and media friendly hype over true journalistic and scientific integrity.

Let me start the longer version with a question. Is your style of eating - your dietary repertoire if you will - the same today as it was 15 years ago? Mine's certainly not. 15 years ago I was a bachelor doing my residency. My diet consisted of burgers, steaks, sausages, pizza, chicken wings, french fries, restaurants, take-out, pots and pots of coffee, and horrible, horrible hospital cafeterias. The fact is, whether it's consequent to life changes, medical conditions, dietary fads, new relationships, new jobs - eating style for many varies wildly with time and circumstances.

Yet the researchers of this paper, one that looked at the impact dietary style would have on cardiovascular risk among 43,396 Swedish women, which concluded that women who followed low-carb diets had an increased risk of heart disease, used only one single baseline dietary data set upon which to base their 15 years long study and its conclusions.

And about that single, solitary, data set.  It consisted of a food frequency questionnaire in which subjects were asked to identify how frequently they consumed 80 different food and beverage items over the course of the past 6 months.

Think that'd be accurate? Can you remember how many of anything, let alone 80 items, you've had over the past 6 months? And what if you ate and drank more than 80 items?

But let's not guess about accuracy, let's actually look at it.  Taking the study subjects' reported average caloric intake, it's immediately evident that their dietary recall data is inaccurate as the authors report an average daily calorie consumption of only 1,561 calories.  That's an incredibly small number, and one which flies in the face of the Food and Agriculture Organization of the United Nations reporting of a Swedish per capita average calorie consumption of 2,990 calories during the same time period this study's data was collected.

But let's for a moment pretend that the data was in fact accurate and that you could fairly extrapolate that your style of eating today will remain the same for the next 15 years. My next question would be do you think the quality of your diet's various proteins, carbohydrates and fats might have a bearing on your risk of developing cardiovascular disease over the next 15 years? Would eating a diet higher in trans-fats confer a different degree of risk than a diet higher in unsaturated fats? Would eating a diet rich in whole grains confer a different risk than a diet rich in ultra processed pulverized flours? How about if you ate out regularly versus cooked from scratch? Deep fried versus baked? Sausages versus salmon? Quinoa versus white rice? Kale versus potatoes?  Of course it would matter, and thats a fact that I'd bet even a straw poll of 10 year olds would agree with.

Not this paper's researchers.  You see they simply reported and analyzed the data from that single time point questionnaire by means of 10 different centiles of carbohydrate consumption. They didn't pay any attention to the quality of the macronutrients being consumed, just their total quantities.  The only consideration they gave as to the quality of macronutrients was a very broad "animal protein" vs. plant sources. There was no consideration given to quality of fats (this despite the well established impact of trans-fat on increasing cardiovascular risks and on unsaturated fats for decreasing them), or carbohydrates (again despite data suggesting cardio-protective benefits from whole grain and risk from refined).

But ok, let's even pretend for a moment that the data was in fact well controlled for dietary factors known to impact on cardiovascular disease, is the risk reported here worthy of concern and press release? Here the relative risk increase of 5% per increase in low-carb score means an extra 4-5 cases of cardiovascular disease per 10,000 women in the lowest carb group per year. Should we stop the presses?  Given how incredibly small that is absolutely, and given how incredibly complicated it is to control for confounding variables (and here I'm not just talking about the unbelievably glaring confounders that were explicitly ignored by the researchers but non-dietary and lifestyle variables of which this study looked at very few), can and should cautionary conclusions truly be drawn let alone publicized?

Lastly let's pretend for a moment that data is in fact conclusive and that the risk is real and scary enough to shout from the rooftops.  Do you think then it would matter if the diets studied and were being reported as risky weren't in fact "low-carb" given that the caution being shouted is that low-carb dieting increases the risk of heart disease?   Looking at the data, the 1st quartile of lower carb consumption is in fact a diet where the 154.7g of carbohydrates account for 40% of calories. Simply put, that's not a low-carb diet! Atkins for instance starts at just 20g and then over time people tend to work themselves up to between 50-100g. 154.7g?  That's.  Not.  Low.  Carb.  Nor is even their reported 10th percentile at 123.7g or 32% carbohyrdate.

So to review. The paper's basing all of its 15 years worth of conclusions off of a single, solitary, and clearly inaccurate, baseline food frequency questionnaire, it didn't control for clearly known smack-you-in-the-face dietary confounders, it found just a miniscule absolute increase in risk, and the diet it's reporting on can't even be fairly referred to as a low-carbohydrate diet.

Useful?  Conclusive?  Press worthy?

It gets worse.

Here the BMJ didn't just publish a completely useless paper, they gave this very clear, yet completely non-evidence based advice to clincians in their accompanying editorial,
"Despite the popularity of these diets, clinicians should probably advise against their use for long term control of body weight"
Worse still highly reputable socially networked curators of medical information tweeted the resultant media stories as relevant and even Journal Watch, a New England Journal of Medicine publication reported it as valuable to scores of physician subscribers who trust Journal Watch to keep them abreast of the latest important journal studies.

As far as the true state of the evidence on the long term risks or benefits of low-carbohydrate diets goes this paper, and the BMJ's editorialized conclusions, add absolutely nothing.  Given the paper's scientifically horrifying flaws and the editorial's completely clueless conclusion they're useless contributions to the medical literature.  In fact I'd describe them as worse than useless in that they're unforgivably, irresponsibly, shamefully and knowingly misinformative - something our already incredibly nutritionally confused world really didn't need.

[For another take on this paper by someone who also actually read the paper, have a peek at Larry Husten's take on Cardiobrief (I'm quoted there too).]

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  1. To me, this is more evidence to the fact that physicians and the medical community in general (with a few exceptions) are clueless about nutrition. It's sad. No wonder the public is so confused.

    1. Nutrition isn't taught in med school. It gets a mention sometimes but it is not a full fledged class in any med school I'm aware of (and I went to one, as a PhD but I took school med school classes and I've verified this at multiple top med schools).

      So, really, what can we expect?

  2. Yes it was really very bad - for all the points you raise. Also this:

    In the conclusion it says:
    "Low carbohydrate-high protein diets, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are associated with increased risk of cardiovascular disease".

    Of course the implication is that low carb is bad - but note, is *associated* with. It is not necessary causal, there was no evidence of causality at all.

    An equally valid, or maybe even more valid, conclusion is “the requirement to lose weight on a regular basis… is associated with increased risk of cardiovascular disease”

  3. "follow the money" is often useful. Perhaps this study was funded by a food company looking to protect it's products from ridicule.

  4. Kristine3:26 pm

    All I can say is, Bravo Yoni!

  5. That is appalling. I eat normally (whatever that is) and 150 g carbs can be normal for me in a day, So can 250! "Low carb" can be anything from 20 g to 40% of total cals and if you're an active guy that can be a jolly lot of carbs!

  6. "Simply put, that's not a low-carb diet! "

    That's what I said!

  7. Anonymous5:27 pm

    I lower my carb intake because of my weight loss program called Roca Labs that is helping me eating less every single day. I know nothing about what and how much carb should only be eaten in a day but I'm almost there of reaching my weight goal and starting to be physically, emotionally and mentally fit. I only need 10 more lbs to achieve it. The important thing for me right now is I'm losing weight by eating less and I think that's healthy.

  8. Anonymous2:15 pm

    I've seen this article quoted in a couple of places this week - one on huffpost and I can't remember wherelse, but people who should know better are giving this article more validity than it deserves.

  9. Anonymous6:37 pm

    It's frightening that articles such as these are published without any proper science, logic, or understanding of nutrition!! Your criticism of the article is very articulate, and filled with so many good points, thanks!

  10. Ive been using low carb and high protein diets for almost 30 years, training both recreational and elite athletes in combat sports. There has been no instances of ill health, or adverse effects, in fact all i reccommend is lots of lean meat, eat eggs every day, eat beans/pulses every day, some citrus fruit, eat lots of green leafy veg go easy on potatoes, rice, pasta, bread and root vegetables and they will make losing weight/fat, keeping strength, tone and health very easy. Its what i was taught by my grandparents, by old coaches and common sense. Micro nutirition and calorific values comes into play with more of the elite athletes but for beginners and the obese. Basic nutrition works! A good article by the way! You have earned another subscriber.