Bento #3

Relentlessly Chasing Macronutrient Magic

Some people call it the macronutrient wars. We call it a relentless pursuit of macronutrient magic. Consumers want to eat healthy, whatever that is. In the 1980s and 90s, it was low fat. In this millennium, that’s shifted to low-carb and keto approaches. But a new study in JAMA Internal Medicine offers a clue that this magic is likely an illusion. Neither low-fat nor low-carb dietary behaviors predict a longer life.

What does? Dietary quality. The authors of this study conclude that the mortality associated with different dietary patterns may depend more on the quality and source of nutrients than on carbs and fats per se.

Observations and Correlations

Right up front, we have to offer a bit of caution about this research. It uses observational data from NHANES on roughly 37,000 people over 15 years. Like most studies of this type, the research depends on self-reports of eating behavior. So you can be sure it’s no more reliable than human memories sprinkled with wishful thinking.

Nonetheless, the findings line up with findings from randomized, controlled studies comparing low-fat and low-carb diets. Results vary from person to person, but neither approach is clearly superior.

And that’s what they saw in this analysis. Neither low-carb nor low-fat dietary patterns themselves had any significant association with mortality. What did have a significant correlation were measures of “healthy” low-fat or low-carb diets.

Finding What You Look For

Another reason we take these correlations with a grain of salt is the phenomenon of confirmation bias. The researchers constructed their own scoring systems for healthy and unhealthy low-fat or low-carb diets. They based their scores on things like the quality of carbs, protein sources, and saturated fat. In other words, they used prior observations of the qualities of nutrients that correlate with good health outcomes to make a measure of diet quality.

No surprise, prior correlations proved to be reliable in this study of correlations. As the authors concede, “because of the observational nature of the study design, we could not determine any causality.”

Indeed, we accept the suggestion that macronutrient magic is not going give us a longer life. It’s also reasonable to think that dietary quality is important. But we don’t have any final answers about what constitutes a high standard for dietary quality. Lots of people have good ideas based on observational studies. And yet there’s plenty of room left for further studies and debates.

Click here for the study and here for further perspective.

Bento #3, photograph © vigilant20 (דָרוּך) / flickr

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January 25, 2020