Friday, July 6, 2012

Low Carb Diets Killing Swedish Ladies Like You Read About

Denise Minger hits another home run in regards to this study, which ominously concluded that women who followed "low carb, high protein" diets were at a "significant" risk of increased cardiovascular disease.  Note, this study wasn't an intervention study, and therefore should be taken for what non-intervention studies are worth as regards their ability to tell us what causes what.  Which is to say, it was a  cool math game, not much more.  That said, Denise pulls some "fun" correlations from the "study':

Lo and behold, the researchers help us answer that very question. In a table too unwieldy to capture in a screenshot, they list the incidence rate ratios (age-adjusted) for all cardiovascular disease diagnoses, based on a variety of characteristics unrelated to food:
  • Being a current smoker (versus no smoking history): 2.78 — a 178% risk increase
  • Having a body mass index in the “obese” range (versus in the normal range): 2.48 — a 148% risk increase
  • Having a body mass index in the “underweight” range (versus the normal range):2.17 — a 117% risk increase
  • Having a hypertension diagnosis (versus no hypertension): 2.50 — a 150% risk increase
  • Having the highest self-rated level of physical activity (versus the lowest): 0.37 — a 63% risk decrease
  • Having over 13 years of education (versus 10 or less): 0.45 — a 55% risk decrease
  • Being over 170 cm in height (67 inches, or 5’7″) (versus being 160 cm/63 inches or under): 0.77 — a 23% risk decrease
Compared with things like going to school for a few extra years and not being vertically challenged, the risk associated with the “low carb, high protein” diet score is minuscule!
But frankly, it hardly matters anyway. All these numbers are based on a single survey from 1991 – ’92, with absolutely no follow-up questionnaires to see if the women’s diets or lifestyles changed afterwards. This whole study rests on the assumption that 44,000 women not only accurately reported their yearly food intake in the early ’90s, but that they kept eating, exercising, and weighing the same for the next 16 years. (Or conversely, that whatever they ate in 1991 singlehandedly determined the fate of their health for the rest of their lives.)
To sum it all up…
  1. This study is observational—meaning it tells us nothing about cause and effect.
  2. This study relies on one food frequency questionnaire that the women filled out upon enrollment in the Women’s Lifestyle and Health Cohort. We have no idea what they were eating during the next 16 years.
  3. Women reported their food intake during the early ’90s, when low-fat diets were the gold standard for healthy eating. The most health-conscious women were likely to be eating the most carbohydrate at that time.
  4. Food frequency questionnaires are all sorts of terrible and don’t let anyone ever tell you otherwise.
  5. The study’s “diet score” design assumes that all low-carbohydrate diets are necessarily high in protein—resulting in a point-assigning system that doesn’t always identify true low carbers.
  6. The women with the lowest carbohydrate intake in this study were still eating up to 123 grams of it a day (an amount that’s probably wildly underestimated, to boot)—meaning they weren’t actually eating a low-carbohydrate diet.
  7. The true increase in cardiovascular disease risk from scoring high on the “low carb, high protein” scale is pretty minor—and pales in comparison to other lifestyle variables.
That’s it!   
I really enjoy Denise's sense of humor, and if you are a food science geek like me, I highly recommend you read the entire post.

Here's another digestion of the study.  The author makes a bunch of good points, just one of which has to do with identification of this variable:
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.

One of the factors in the study is simply goofy, but it is a mistake often made by those who fear low carb but do not understand low carb diets.  The mistake is thinking of low carb as "high protein."  It is quite difficult to eat a truly high protein diet, because most of the ways a human can down a lot of protein require that a human also eat fat.  Also, truly high protein diets are not the best weight loss diets, as they preclude ketogenic metabolism; the gluco-neogenesis associated with protein intake interrupts ketogenesis.
It always makes me wonder - why does anyone fund studies like this?  There are good intervention studies that show a better result in the short term for carb restriction.  There is no possible factor yet identified that could account for why eating low carb short term might be good but that would make it bad for the long term.  There have already been plenty of observational studies that show all kinds of correlations.  All that's left is to fund good, long term, intervention studies.  Expensive?  Yes, expensive as all get out.  But the cost benefit of another cleverly designed observational study is zero.  Just stop it folks.
The other thing I wonder is - why do folks publish these mis-informative articles?  Easy news?  No one understands even the basics of the scientific method?  There are many reasons, none very satisfying.
In summary, I don't think the Swedish ladies in question were killed by their "high protein low carb" diets.
Eat meat, eggs, vegetables, nuts and seeds, little fruit or starch, no sugar/wheat.  If you are lean, feel good, perform well, have little hunger, and demonstrate good glycemic control, you'd be crazy to let studies like this deter you.

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