Re: Low carbohydrate-high protein diet and incidence of cardiovascular diseases in Swedish women: prospective cohort study
Let me start this response 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 and shamefully misinformative - something our already incredibly nutritionally confused world really didn't need.
(Originally published on my blog at http://www.weightymatters.ca/2012/06/what-reading-that-low-carb-gives-yo...)
Competing interests: Author of Simon & Schuster published book on fallacies of modern day dieting slated for publication Spring 2013