Dieters often overestimate how healthy they’re actually eating, Harvard study shows

BOSTON — On a diet? There’s a good chance you’re not actually eating as healthy as you think, suggests a new Harvard study.

Dieters actively try to make healthier choices, whether swapping dessert for fruit or snacking on celery with peanut butter instead of chips. But the new research finds people overestimate how much change they’ve made to their overall, with most retaining their usual eating patterns.

“We found that while people generally know that fruits and vegetables are healthy, there may be a disconnect between what researchers and health care professionals consider to be a healthy and balanced diet compared to what the public thinks is a healthy and balanced diet,” says study author Jessica Cheng, PhD, a postdoctoral research fellow in epidemiology at the Harvard T. H. Chan School of Public Health, in a statement. Cheng also practices general internal medicine at Massachusetts General Hospital.

Almost half of adults living in the United States try to lose weight, with the first step being to modify their diets. People try incorporating more fruits and greens in their meals, which is great for heart health and longevity. The current study evaluated how effective people thought their diet was at losing weight versus the reality of their weight loss journey.

Researchers tracked the diets of 116 adults aged 35 to 38 who were actively trying to shed pounds. All of the participants met with a dietitian to discuss their nutrition and recorded their food and drink intake for the entire year using the Fitbit app. People were weighed daily with the Fitbit watch tracking their physical activity.

At the beginning and end of the study, the researchers calculated each person’s Healthy Eating Index (HEI) score. The HEI is a measure that lets researchers know how a person’s dietary patterns line up with the U.S. Dietary Guidelines for Americans. Between 0 to 100, the higher the score, the healthier the diet. People were asked to recall what they ate the last two days, with the score going up for foods like fruits and whole grains and going down for unhealthier choices.

Before they received their HEI scores, the team asked participants to rate how healthy they felt their diet was before and after the study. People whose self-perceived score was between six points of their HEI score were considered in “good agreement.”

Reality versus perception when it comes to dieting

One in four people had realistic views of their diets as their self-score closely matched their HEI score. However, three out of four people had misleading perceptions of the quality of their diet. Nearly 75% thought they maintained a healthy diet, scoring themselves as 67.6. But in reality, the average HEI score was 56.4.

When evaluating their diet after a year, only 1 in 10 people had accurate perceptions of their dietary changes. After the experiment ended, the researchers calculated people’s HEI scores going up by one point. However, most people rated themselves as making grand improvements, estimating their score would go up by 18 points.

“People attempting to lose weight or health professionals who are helping people with weight loss or nutrition-related goals should be aware that there is likely more room for improvement in the diet than may be expected,” says Dr. Cheng. “Future studies should examine the effects of helping people close the gap between their perceptions and objective diet quality measurements.”

One way people can be more self-aware of what they’re eating is to seek out information on what areas of their diet can be improved and ways to make healthy nutritional changes. It may also make people less likely to give up on their weight loss goals when they experience minor setbacks.

“Overestimating the perceived healthiness of food intake could lead to weight gain, frustrations over not meeting personal weight loss goals or lower likelihood of adopting healthier eating habits,” adds Deepika Laddu, PhD, an assistant professor in the College of Applied Health Sciences at the University of Illinois, Chicago, and chair of the American Heart Association’s Council on Lifestyle Behavioral Change for Improving Health Factors. “While misperception of diet intake is common among dieters, these findings provide additional support for behavioral counselling interventions that include more frequent contacts with health care professionals, such as dieticians or health coaches, to address the gaps in perception and support long-lasting, realistic healthy eating behaviors.”

The study did have some limitations that could make generalizing the findings to the public difficult. To start, more than three-fourths of the participants were women, and 84% were Caucasian. This omits the cultural factors that shape a person’s diet and perception of nutritious foods. They also did not assess for diet quality perceptions throughout the year, which could have helped understand when people became more realistic about the nutritional value of their dietary choices.

The research was presented at the American Heart Association’s Scientific Sessions 2022.

About the Author

Jocelyn Solis-Moreira

Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master’s of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor’s of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women’s health.

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