For today’s edition of Dear Mark, I’m answering a single, significant question. It concerns the latest “anti-low-carb” study claiming that we’re all killing ourselves by not eating bread. A reader wonders if the study is legit and if we should be worried about eating fewer carbs than “normal” people.
I don’t think we should be concerned, and I’ll explain why in detail. Let’s take a look and break it down.
I’m sure you’ve seen this latest study to claim that low-carb diets will kill us all: https://www.thelancet.com/journals/lanpub/article/PIIS2468-2667(18)30135-X/fulltext
Is it legit?
Yes, I’ve seen it.
Where to start?
This study came from Walter Willet, he of the voluminous mustache and unbridled enthusiasm for seed oils.
The most glaring weakness is the way they gathered the data. Over the course of 25 years, participants were asked to accurately report their diet reaching back as far as six years. This is an inherent issue in most nutrition data gathering, so it’s not unique to this study, but come on. Can you remember what you ate 6 years ago? Did your diet change at all, or was it stable enough to encompass with a curt summary?
The characteristics of the participants differed greatly.
Low-carbers were far more likely:
- To be men—Males have a higher risk of mortality than women.
- To be diabetic—Diabetes lowers lifespan, especially in the 1980s (when the bulk of the data was collected).
- To be sedentary—Failure to exercise is a major risk factor for early death, and ill health in general.
- To smoke cigarettes—Again, this is an elementary variable. Nothing like being able to smoke indoors. Remember smoking sections on airplanes? I do.
- To eat fewer fruits and vegetables—Carnivory is popular these days, and may work for some, but plants are still good for you and actually complement a low-carb, high-meat diet quite nicely.
- To be overweight—All else being equal, the fatter you are, the unhealthier you are.
Even if they were able to “control for” all those variables, you can’t control for the overall health and wellness trajectory of a person hellbent on ignoring their personal health. What other unhealthy things are they doing that weren’t captured and accounted for by the researchers?
For instance, alcohol intake. They didn’t look at alcohol intake in this trial. Seriously, search for “alcohol” in the paper and you’ll come up blank. It’s very likely that the low-carbers were drinking more alcohol, as similarly-conducted epidemiological research has found that “carbohydrate intake [is] the first to decrease with increasing alcohol consumption.” (2) Alcohol can take a serious toll on health and lifespan if you aren’t careful with your intake.
Oh, and low-carbers were also more likely to be on a diet. This might be the most crucial variable of all. Who goes on a diet, typically? People who have a health or weight problem. Who doesn’t diet? People who are happy with their health and weight. There are exceptions to this, obviously, but on a population wide scale, these trends emerge. Did the low-carb diet actually reduce health and lifespan, or did the health conditions that prompted the diet in the first place reduce health and lifespan?
Ultimately, this was all based on observational studies and epidemiological data. It can’t establish cause-and-effect, it can only suggest hypotheses and avenues for future research.
Luckily, we have controlled trials that demonstrate the health benefits of low-carb dieting, all of which correspond to better longevity:
You could make the argument that the positive health effects are purely short-term and that in the long run, those benefits turn to negatives. It wouldn’t be a very good argument, though, because we don’t have any indication that it actually happens. If you go reduce carbs or go keto and you lose body fat, gain lean muscle, improve your fasting blood sugar, normalize your lipids, and reduce inflammatory markers, I see no plausible mechanism by which those improvements lead you to an early grave. Do you?
It seems the burden of proof lies in the Willet camp. If the only healthy range of carbohydrate intake is between 50-55%, he would have to show that:
- No healthy, long-lived cultures or individuals have a carbohydrate intake that strays from the 50-55% range. Anthropological and ethnographical evidence must confirm.
- The benefits of low-carb diets, established through randomized controlled trials, are illusory and/or transitory, eventually giving way to health decrements that lower lifespan.
That’s a tough one. Hats off if he can pull it off. I doubt he can.
Thanks for writing in. I hope I allayed any concerns you might have had.
Take care, all, and be sure to share down below with your own comments and questions.
1. Seidelmann, Sarah, MD, et al. Dietary Carbohydrate Intake and Mortality. Lancet. 2018. (Online First)
2. Liangpunsakul S. Relationship between alcohol intake and dietary pattern: findings from NHANES III. World J Gastroenterol. 2010;16(32):4055-60.
3. Thorning TK, Raziani F, Bendsen NT, Astrup A, Tholstrup T, Raben A. Diets with high-fat cheese, high-fat meat, or carbohydrate on cardiovascular risk markers in overweight postmenopausal women: a randomized crossover trial. Am J Clin Nutr. 2015;102(3):573-81.
4. Ballard KD, Quann EE, Kupchak BR, et al. Dietary carbohydrate restriction improves insulin sensitivity, blood pressure, microvascular function, and cellular adhesion markers in individuals taking statins. Nutr Res. 2013;33(11):905-12.
5. Rajaie S, Azadbakht L, Saneei P, Khazaei M, Esmaillzadeh A. Comparative effects of carbohydrate versus fat restriction on serum levels of adipocytokines, markers of inflammation, and endothelial function among women with the metabolic syndrome: a randomized cross-over clinical trial. Ann Nutr Metab. 2013;63(1-2):159-67.
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