House of Cards

The House of Cards That Links Diet, Obesity, and Health

The most pervasive way of thinking about obesity is to simply regard it as “a diet-related disease.” But a new paper in Nature Food suggests we may be misleading ourselves. That’s because of a fundamental problem in the data that links patterns of diet to obesity and health. An impressive collection of scientists examined the reliability of self-reports about dietary energy intake from 128 different studies. They concluded it is unreliable, writing:

“The macronutrient composition from dietary reports in these studies was systematically biased as the level of misreporting increased, leading to potentially spurious associations between diet components and body mass index.”

This matters when food labels start telling people that this food is “healthy” or that food is not, based upon spurious associations with obesity.

Comparing Self-Reports to Direct Measurement

To reach this conclusion, the researchers used actual measurements of the total energy a person uses as a check on their self-reports of how much they consumed. The direct measurements come from a method that uses doubly-labeled water.

The numbers don’t match up. This is not an entirely new observation. Scientists have long known that people under-report how much they eat. So they’ve developed methods for adjusting self-reports to account for that misreporting. But here’s the rub: Even those adjusted numbers were wrong. The authors of this new study examine data from NHANES and NDNS and show:

“The level of dietary under-reporting is underestimated by previous tools and that this introduces bias in evaluating dietary composition.”

This Is a Problem

The message we take from this is quite simple. This is a problem if we rely on links in self-reported data to call obesity a diet-related disease and use them to tell people what to eat for better health. Gary Frost, Chair of Nutrition and Dietetics at Imperial College London, explains:

“If you want to try and set policy around food based on this type of data, then obviously your policy is fundamentally flawed to some extent. We’ve got to try and find new methodologies to actually understand what people consume.”

This is a problem that is solvable – so long as serious scientists and policy makers face up to it.

Click here for the study in Nature Food, here and here for further perspective.

House of Cards, photograph by Peter Roberts, licensed under CC BY 2.0

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January 26, 2025