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ROCKVILLE, Md. — Almost everyone thinks their diet is far healthier than it actually is, according to a new study. In fact, of the nearly 10,000 people researchers looked at, only 15 percent could accurately tell how healthy their diet was.

Moreover, those with the worst diets had the best idea of how unhealthy it was! Of the 85 percent who got it wrong, almost all of them (99%) overrated its healthiness.

Previous studies have found that self-rated health is a strong predictor of bad health and death, but there has been little research on whether self-rated diet quality is accurate. With that in mind, a team from the U.S. Department of Agriculture’s Agricultural Research Service decided to look into how healthy self-rated diets actually are.

The study used data from the National Health and Nutrition Examination Survey, a nationally representative survey of American adults conducted every two years. Participants were asked to complete detailed 24-hour dietary questionnaires and rate their diet as excellent, very good, good, fair, or poor.

Researchers also used the food recall questionnaires to score each participant’s diet quality. Types of foods ranked as healthier included fruits and vegetables, whole grains, healthy fats, lower-fat dairy products, seafood, and plant proteins.

Foods considered less healthy included refined grains and foods high in sodium, added sugars, or saturated fats.

“We found that only a small percentage of U.S. adults can accurately assess the healthfulness of their diet, and interestingly, it’s mostly those who perceive their diet as poor who are able to accurately assess their diet,” says research epidemiologist and lead author Dr. Jessica Thomson in a media release.

“Additionally, most adults overrate the quality of their diet, sometimes to a substantial degree.”

Some people eat unhealthily — and they know it

Researchers discovered serious disconnects between the calculated scores and how participants rated their own diets. Out of the more than 9,700 people who participated, roughly 8,000 (85%) had the wrong perception about the quality of their diet. Nearly every person in this group said their diet was healthier than it really was.

Surprisingly, participants with a “poor” diet displayed the highest accuracy — matching the researcher’s ratings of their diet 97 percent of the time.

“It’s difficult for us to say whether U.S. adults lack an accurate understanding of the components of a healthful versus unhealthful diet or whether adults perceive the healthfulness of their diet as they wish it to be—that is, higher in quality than it actually is,” Dr. Thomson concludes.

“Until we have a better understanding of what individuals consider when assessing the healthfulness of their diet, it will be difficult to determine what knowledge and skills are necessary to improve self-assessment or perception of one’s diet quality.”

The team presented their findings at NUTRITION 2022 LIVE ONLINE, the flagship annual meeting of the American Society for Nutrition.

South West News Service writer Jim Leffman contributed to this report.

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