You probably think your diet is more healthy than it actually is, according to new research.

One of the most enduring truisms about life may very well be that the better food tastes, the worse it must be for your health. Judging from the results of a new study, while Americans can very well judge how tasty a certain dish is, they’re not as adept at gauging its healthiness.

Overestimation

“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,” said Jessica Thomson, PhD, research epidemiologist with the U.S. Department of Agriculture’s Agricultural Research Service in the Southeast Area, the study’s lead author.

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

The findings are based on data from the National Health and Nutrition Examination Survey, a nationally-representative survey of U.S. adults that is conducted every two years. Participants of this study were asked to detail their diet over the last 24 hours and rate their diet via a series of questionnaires. Diets could be described as excellent, very good, good, fair, or poor.

According to the authors, previous research has shown that self-rated diet quality is a good predictor of morbidity and mortality, but we don’t really have any evidence to show whether self-rated dietary information is reliable or not. This lack of knowledge prompted the current study.

The goal of the study was to find out whether a single, clear question could be used as a screening tool for other nutrition studies. Such a question can be used to complement or even replace the more detailed, but also much more lengthy, dietary questionnaires currently in use in nutrition research. The usefulness of such a single question, however, would rely on self-reported dietary data being reliable — so the team set to test this out.

Based on the food recall questionnaires in the National Health and Nutrition Examination Survey, the team gauged the dietary quality of each individual participant. Some of the items that they ranked as being healthier included fruits and vegetables, whole grains, healthy fats, lower-fat dairy products, seafood, and plant proteins. Foods that were considered to be less healthy included refined grains, items high in sodium, or those with high levels of added sugars or saturated fats.

According to the findgins, there are significant discrepancies between the health scores as calculated by the researchers and the participatns’ own rankings. Out of the 9,700 participants analyzed in this study, around 8,000 (or 85% of the total) provided an inaccurate assesment of their diety quality. Virtually all of them (99% of these 8,000) were biased towards rating their diet as being more healthy than the researchers calculated them to be.

One surprising finding was that participants who rated their diet as ‘poor’ were the most accurate in their assesments. Their ratings matched those of the researchers 97% of the time. For the other cateogories, accurate assesments ranged between 1%-18%.

The findings showcase that self-reported diet quality data is most often unreliable, but it is yet unclear as to why. More research is needed to determine what factors people look to when asked to asses their diets. Thomson explains that it would be useful to know, for instance, whether people are actually aware of healthy diet recommendations, and whether they take into account the source and method of preparation of their food.

“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,” she adds. “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 findings will be presented Tuesday, June 14, at the NUTRITION 2022 LIVE ONLINE Relationship Between Dietary Patterns and Behavioral/Societal Outcomes session.