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Most people overestimate the healthiness of their diet

Foods that are available for us to purchase in supermarkets and stores are not all equally healthy. And, although many people keep track of the amounts of fat and sugar in the food they buy, this is not the whole story when it comes to eating healthily. Despite all the information and guidance available, it seems that Americans still struggle to eat a healthy diet.

A new study on just how American perceptions of a healthy diet differ from reality is to be presented by Jessica Thomson at Nutrition 2022 Live Online, the flagship annual meeting of the American Society for Nutrition.

In this study, the researchers used data from the National Health and Nutrition Examination Survey, a nationally representative survey of U.S. adults conducted every two years. Over 9,700 participants were asked to complete detailed 24-hour dietary recall questionnaires and rate their diet as excellent, very good, good, fair or poor. The researchers then used the questionnaires to assess the quality of each participant’s diet. 

In this respect, healthier diets were considered to be those that included fruits and vegetables, whole grains, healthy fats, lower-fat dairy products, less sugar, and proteins from seafood and plants. Foods considered less healthy included refined grains and foods high in sodium, added sugars or saturated fats.

Apart from assessing diet quality, the researchers wished to find out whether a single, simple question (How healthy is your diet?) could be used as a screening tool to replace the detailed dietary questionnaires currently used in nutritional studies. Previous studies have found that people are accurate at assessing the state of their health overall, and that self-rated health is a strong predictor of morbidity and mortality. Currently, however, there is little research on whether self-rated diet quality is predictive of the actual quality of one’s diet.

The results of the study showed that people’s assessment of the healthiness of their diet did not agree with the researcher-calculated scores obtained from analysis of the detailed diet questionnaires. Participants tended to overrate the healthiness of their diets. Of the over 9,700 participants, about 8,000 (roughly 85 percent) inaccurately assessed the quality of their diet. Of those, almost all (99 percent) overrated the healthiness of their diet.

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

Among those who rated their diet as poor, their assessment matched that of the researchers in 97 percent of instances. However, in the other dietary categories the assessment by the participants only matched that of the researchers in 1–18 percent of cases. This represents a significant and concerning disconnect between the researcher-calculated scores and how participants actually perceived their own diets.

“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,” said Thomson. “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.”

Clearly, using a person’s answer to the question ‘How healthy is your diet?’ is not going to provide an accurate assessment, or replace the detailed diet questionnaires currently used in nutritional studies. Thomson said further research could help to elucidate what factors people consider when asked to assess their diet quality. For instance, it would be helpful to know whether people are aware of particular dietary recommendations and whether they take into consideration where their food is purchased or how it is prepared. 

By Alison Bosman, Staff Writer

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