Most people think their diet is healthier than it really is — but people with the least healthy diets are far less likely to overestimate the nutritional value of what they eat, according to new research presented at Nutrition 2022 Live Online, the annual conference of the American Society for Nutrition, and described in a press release from the organization.
Right now, it’s standard practice for studies that look at the health impacts of diet quality to ask participants a series of complicated questions about what they ate recently — sometimes known as a dietary recall questionnaire. The researchers then assess the nutritional quality of participants’ diets based on these responses — potentially focusing on specific components of the diet, depending on the goals of the study. This is a time-intensive process for both study participants and researchers, and it’s based on the premise that at least when it comes to overall diet quality, participants can’t be trusted to assess their own diet. Instead, the thinking goes, researchers need to apply a standard method to assess how healthy a person’s diet is.
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For the latest study, the researchers were interested in whether asking participants about their diet quality directly could potentially replace complicated dietary recall questionnaires for some future studies on diet quality and health. If people are generally good at assessing how healthy their diet is, this might be possible, but it wouldn’t work if people are bad at estimating how healthy their diet is. Based on this standard, it looks like dietary recall questionnaires won’t be going away anytime soon.
Over 9,700 participants completed a dietary recall questionnaire as part of the study, and also answered whether they thought their diet quality was poor, fair, good, very good, or excellent. The researchers then assessed participants’ diet quality based on the food questionnaire responses — both overall and in the specific areas of vegetable intake, fruit intake, dairy foods, sodium, and added sugars.
Most overestimate the quality of their diet
The researchers found that about 85% of participants were not accurate in their assessment of their diet quality — and out of those who inaccurately assessed their diet, 99% estimated that it was healthier than it actually was. In assessing diet quality, the researchers considered healthier foods to include fruits and vegetables, whole grains, healthy fats, lower-fat dairy products, seafood, and plant proteins. They considered unhealthier foods to include refined grains and foods high in sodium, added sugars, or saturated fat.
The notable exception to inaccurately assessing diet quality was participants who rated their diet as poor — in this group, researchers’ assessment matched participants’ rating 97% of the time. For the other four groups, though, the percentage of participants whose rating was supported by the researchers’ assessment ranged from only 1% to 18%.
Among participants who accurately rated their diet quality, diet scores for each of the specific areas — vegetable intake, fruit intake, dairy foods, sodium, and added sugars — tended to match the overall diet score. The one exception was dairy foods, for which participants with an excellent overall diet score tended to have an even worse score than for participants whose overall diet score was poor, fair, good, or very good. This result suggests that even people with the healthiest diets might overestimate how healthy certain full-fat dairy foods are.
“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,” said study author Jessica Thomson, PhD, a research epidemiologist with the U.S. Department of Agriculture’s Agricultural Research Service, in the press release. “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.”