Red Cabbages, Rhubarb and Orange

Cabbage Crowned, Lettuce Loses in Nutrition Correlation

Is nutritional epidemiology suffering from overexposure? A study of veggies and COVID-19 mortality prompts this question. This exercise in nutrition correlation comes from a pre-print. So we can’t blame lax peer reviewers for this one. But the manuscript does make some remarkable claims:

For each g/day increase in the average national consumption of some of the vegetables (head cabbage and cucumber), the mortality risk for COVID-19 decreased by a factor of 11, down to 13.6%. Lettuce consumption increased COVID-19 mortality.

Cancel Nutritional Epidemiology?

This study moved Tamar Haspel in the Washington Post to write:

Those of you who come here often know that I’ve railed about nutritional epidemiology before; I think it’s so flawed, and the flaws are so intractable, that we should simply stop doing it.

It is indeed a tool suffering from overuse and misuse. We do tire of endless bickering about saturated fats, eggs, meat, whole-fat dairy, carbs, and more. We are not alone in our impatience. John Ioannidis poked the hornet’s nest a few years ago when he wrote in JAMA:

The emerging picture of nutritional epidemiology is difficult to reconcile with good scientific principles. The field needs radical reform.

Of course, epidemiologists who’ve built their careers on big observational databases don’t like this idea. Criticism of nutritional epidemiology is nonconstructive and naive, they say.

Test the Observations

Protestations from the land of epidemiology would be more impressive if they moved on to testing their observations. Experiments are the bedrock of science. When the lions of epidemiology declare that controlled studies can’t be used for nutritional science, it’s hard to keep a straight face.

So we must move on. When we see a correlation of nutrition behavior with poor health outcomes, it makes sense to test ways to change the behavior. But that’s not enough. We must know that changing the behaviors causes a change in health outcomes.

Haspel some targets for research – like portions, convenience, education, and consumer preferences. These are all decent ideas, and many more have merit, too. But good ideas are not enough. The ideas must translate into results of better health. Not just desired behaviors.

Ideas that actually improve lives and health become sustainable policies. Others go down as failed experiments.

Click here for the commentary from Haspel and here for more on the need for more rigor in nutrition and obesity research. For the dodgy study of lettuce, cabbage, and COVID, click here.

Red Cabbages, Rhubarb and Orange, painting by Charles Demuth / WikiArt

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July 26, 2020