People trying to adopt a healthier diet probably aren't the best judges of how well they're actually eating, a new study discovers.
Only about 1 in 4 people could accurately estimate how healthy they were eating when asked to assess their diet after a year spent trying to lose weight, researchers found.
Worse, only 1 in 10 people understood how their diet had actually changed during that year, with most assuming they'd made much greater strides than they actually had.
"There's not very good agreement between what they perceive their diet quality to be and what we've calculated their diet quality to be. They're also overestimating the amount of change that they've made in their diet quality," said lead researcher Jessica Cheng. She's a postdoctoral research fellow in epidemiology at the Harvard T.H. Chan School of Public Health in Boston.
"And so that was really the big takeaway here, that there might be some disconnect among people trying to diet with both how healthy they think their diet is and how much change they think they've made in their diet over the course of attempting to lose weight," Cheng added.
Cheng will present these findings at this weekend's annual meeting of the American Heart Association, held in Chicago and virtually. Findings presented at medical meetings are considered preliminary until published in a peer-reviewed journal.
Nearly half of Americans try to lose weight every year, the researchers said in background notes.
But prior research has shown that people tend to overestimate their adherence to healthy eating habits like munching on fruits and veggies, opting for whole grains, choosing lean protein, and substituting nonfat or low-fat dairy for full-fat versions, Cheng said.
To get an idea how far off people can be, researchers evaluated the diets of 116 adults between the ages of 35 and 58 in the Pittsburgh area who were trying to lose weight.
Mismatch between perception, reality
Participants met one-on-one with a dietitian to discuss their nutrition, then tracked everything they ate and drank every day for one year on the Fitbit app.
At the beginning, middle and end of the one-year study, participants were asked to complete a 24-hour food recall questionnaire -- essentially a self-assessment of how well they were eating, based on their personal recollection. Participants also self-scored their beginning and ending diet quality.
Researchers used the actual eating data and the participants' recollections to calculate two separate Healthy Eating Index (HEI) scores, one based on the true diet numbers and the other based on people's perceptions of what they ate.
The HEI is a measure for assessing how closely an eating pattern aligns with the U.S. Dietary Guidelines for Americans. The score runs from 0 to 100, with a higher score indicating a healthier diet.
Only 27% of people had a self-assessment that agreed with their actual HEI score by the end of the study, researchers found.
"Only about a quarter of the sample had good agreement, and so that means 75% of them were off somehow," Cheng said. "Most of this disagreement is coming from people overestimating how good their diet is."
The average perceived HEI score was 67.6, while the actual average score was 56.4.
"They think they are about 10 or 15 points higher than the Healthy Eating Index would suggest," Cheng said.
To put these scores in perspective, the federal Healthy People 2020 initiative set a goal of improving Americans' diet to an average HEI score of about 74, Cheng said.
Researchers also asked the participants to judge how well their HEI score had improved during the year of dieting.
These results were even more off, with only 13% of people accurately assessing how well they'd improved their regular diet.
Diet tracking tools can help
"When you look at how much change that they had in the Healthy Eating Index over the course of the study, it was about 1 to 2 points, which is not a lot on a 100-point scale," Cheng said. "But when you ask them, they're thinking that they're changing their diet quality, on average, by about 18 to 19 points."
These results are "critically important" for understanding the "discrepancies between perceived and actual health behaviors," said Deepika Laddu, chair of the American Heart Association's Council on Lifestyle Behavioral Change for Improving Health Factors.
"If we don't understand initial perceptions and intentions of what a healthy diet is, this could lead -- as we've seen with these findings -- to constant overestimation and consumption of foods that are perceived to be healthy," said Laddu, an assistant professor with the University of Illinois Chicago's College of Applied Health Sciences. "That in turn can lead to weight gain, not to mention increasing frustration over not meeting personal weight-loss goals."
Cheng believes people have a general understanding of what a healthy diet entails, and simply need better coaching and assessment tools to have a realistic understanding of how well they're eating.
After all, wearable tracking tools help people gain an accurate understanding of their daily step count, their nightly sleep quality and their average heart rate. Using an accurate diet tracker could fulfill a similar role.
"The diet advice that's out there is very confusing to people and people have a hard time with it, but I think they really do know the basics," Cheng said. "People know that fruits and vegetables are good for them, and there's not much disagreement about that.
"So I would say, take a step back and think about your basics," Cheng said. "Are you eating your fruits and vegetables? Can I increase my fruits and vegetables? Think about measuring, if you can. Really sit down and say, how many vegetables did I have on Monday and Tuesday and Wednesday, and can I increase those?"
The federal government's MyPlate program is a good place to start, if people would like a relatively simple guide to healthy eating, Cheng added.
"This gives you a nice visual description of what you should be eating," Cheng said.
The U.S. Department of Agriculture has more about MyPlate.
SOURCES: Jessica Cheng, PhD, a postdoctoral research fellow, epidemiology, Harvard T.H. Chan School of Public Health, Boston; Deepika Laddu, PhD, assistant professor, College of Applied Health Sciences, University of Illinois Chicago; American Heart Association, Scientific Sessions abstract and press release, Oct. 31, 2022