We interrupt your regularly scheduled wheat broadcast for an important announcement!
A few of you lovely readers emailed me today (thanks!) about the study Low-Carbohydrate Diets and All-Cause and Cause-Specific Mortality just published in the Annals of Internal Medicine. This paper compares mortality rates for folks eating a so-called “animal-based diet” versus a so-called “vegetable-based diet,” both of them so-called “low carbohydrate.” I finally got a chance to look at it, and indeed, a glance at the abstract looks a little spooky for any low-carb omnivores out there:
A low-carbohydrate diet based on animal sources was associated with higher all-cause mortality in both men and women, whereas a vegetable-based low-carbohydrate diet was associated with lower all-cause and cardiovascular disease mortality rates.
Oh noes! This abstract sounds vaguely China-Study-esque, with the conclusion that plant-based diets are healthier than ones featuring more animal foods. Was this study really comparing hardcore meat eaters with plant noshers, like the abstract implies? Is animal protein poison after all? Is it time to ditch the steaks and bow down in phytoestrogenic reverence to the almighty tofu?
I’ve said it before and I’ll say it again: In most cases, abstracts tell you a whole lotta’ nothing—so don’t judge a study until you’ve read the full text.
For right now, I’ll give this study the benefit of the doubt and ignore the fact that A) the researchers used a pretty lame decile-based scoring system* and B) employed the notoriously unreliable food-frequency questionnaire to collect their data.**
*NOTE: The decile method divvies up dieters into ten levels of adherence—with the folks in the first decile adhering the least to a low-carb diet, and the folks in the tenth decile adhering the most. The reason it’s lame is that it uses a scoring system based on misconceptions about what a low-carb cuisine looks like, including the necessity of a high protein intake.
**UPDATE: For a mighty entertaining explanation of the flaws of this study—including why food-frequency questionnaires are terrible—please read Chris Masterjohn’s take on this whole shebang. If possible, bring a scuba suit.
First, let’s take a look at what the low-carbohydrate folks were actually eating. Click the thumbnails for a bigger pic—first one’s women, second one’s men.
Ha ha ha ha.
I’ll sum it up. Some of the participants were eating up to 60% of their diet as carbohydrates (first decile), which—last time I checked—is kind of not low-carb. Even the lowest low-carb eaters were still eating over 37% of their calories from carbohydrates. Whoever decided to call this study “low carbohydrate” is nuttier than a squirrel turd. That doesn’t mean it can’t offer anything useful, though, so let’s look at what else is going on in the highest decile for each group (which is the only decile the researchers really looked at):
- Folks adhering the most to the animal-based diet were more likely to smoke and had higher BMIs than the best adherents of the Vegetable Group. Along with influencing mortality outcomes, this suggests the Animal Food group, in the highest decile, may have been somewhat less health-conscious than the dieters lumped into the highest decile for the vegetable category. And that’s the type of thing that has repercussions for other diet and lifestyle choices that weren’t measured in the study.
- The Vegetable Group was nowhere near plant-based: They derived almost 30% of their daily calories from animal sources (animal fat and animal protein), versus about 45% for the Animal Group. D’oh!
- The Vegetable Group adherents ate more fruits, vegetables, and whole grains than the Animal Group adherents—which begs the question: What kinds of carbohydrates filled this macronutrient void for the animal-food eaters? Could it’ve been refined grains and processed carbs, which the study conveniently forgot to document?
- For the Vegetable Group, cancer and cardiovascular mortality was lower in the tenth decile than the first decile, even though both deciles ate exactly the same amount of red meat and nearly the same amount of total animal foods. This suggests animal products aren’t the driving force behind differences in mortality rates.
- Similarly, at the fifth decile, the Vegetable Group had a lower cardiovascular mortality hazard ratio than the Animal Group (0.99 versus 1.21), even though the Vegetable Group was eating a slightly greater proportion of animal foods (33.3% versus 29.9% of total energy for women; 32.9% versus 31% for men).
Here are the mortality tables:
And for the dieters scored based on Vegetable Diet adherence, the people with the lowest cancer mortality (male) and cardiovascular mortality (both genders) were not the ones eating the most plant foods—they were the folks in the sixth and seventh deciles, respectively:
Unfortunately, the article doesn’t show us the food/macronutrient breakdowns for any deciles besides the first, fifth, and tenth, so we don’t know what the average diet looked like for these people. But since the vegetable low-carbohydrate score was based on “the percentage of energy of carbohydrate, vegetable protein, and vegetable fat” the dieters consumed, it’s pretty safe to say that the folks in the sixth and seventh deciles were eating less plant foods than the tenth-decilers (and consequently, more animal foods).
Bottom line: In this study, when you look closer at the data, differences in mortality appear to be unrelated to animal product consumption. Changes in cancer and cardiovascular risk ratios occur out of sync with changes in animal food intake.
So what is responsible for the Vegetable Group’s lower mortality hazard ratios (and the Animal Group’s higher ones)?
Here’s a clue. Every time the researchers made multivariate adjustments to the data to account for the risk factors they did document (including physical activity, BMI, alcohol consumption, hypertension, and smoking, among other things), the hazard ratio went down for the Animal Group (meaning it got better) and it went up for the Vegetable Group adherents (meaning it got worse). That indicates pretty clearly that the Animal Group adherents had more proclivity to disease right from the get go, regardless of meat consumption, and the Vegetable Group adherents may have been more health-aware than most folks. (To see what I’m talking about, look at the mortality tables under the “10″ column, and compare the “Age- and energy-adjusted HR” with the “Multivariate-adjusted HR” for each group.)
In other words, it looks like what this study really measured was a Standard American Diet group (aka highest Animal Group decile) and a slightly-less Standard American Diet group (aka highest Vegetable Group decile). Both ate sucky diets, but the latter had slightly less suckage. You can bet the farm that neither was anything close to “low carb.” And if you have two farms, you can bet the other one that neither diet group was anything near plant-based, so I’m not sure the vegan crowd has much to gloat about here.