It feels somewhat unkind to put the boot into people who have been dieting for a year – and tell them that they’re not doing as well as they think they are.

But a new study does just that – finding that most people think they’ve significantly improved the quality of their diet over 12 months, when in fact it barely improves, if at all.

The most useful take-away from the study is that people seeking to lose weight – and, perhaps more importantly, to improve the healthiness of what they eat – would do better by getting professional advice (online or in person) on what a healthy diet looks like.

It seems too that keeping regular records of what you’ve been eating would serve as a check from straying too far into dark (fatty, sugary, salty) side.

The Harvard researchers say the problem is a mismatch between perception and reality – between how a dieter thinks how a diet might have improved, and how healthy it is, and the reality according to a clinical nutrition scale.

But it also seems to be a matter – at least for the participants of this study – of vaguely relying on eating a few more vegetables and fruits, rather than taking a whole-diet approach.

The study

The research was presented at the American Heart Association’s Scientific Sessions held in Chicago earlier this month.

According to a statement from the association, the researchers evaluated the diets of 116 adults aged 35–58 years old who were trying to lose weight.

The participants met one-on-one with a dietitian to discuss their nutrition and then tracked everything they ate and drank every day for one year on the Fitbit app.

They also weighed themselves daily and wore a Fitbit device to track their physical activity.

Dr Jessica Cheng

Researchers calculated a Healthy Eating Index score at the beginning and end of the study based on the types of foods that participants reported eating.

Participants were asked to complete a 24-hour food recall for two days at each time point.

The HEI is a measure for assessing how closely a dietary pattern aligns with the US government’s Dietary Guidelines for Americans.

A score of 0 to 100 is possible, with a higher score indicating a healthier diet. The score is based on the frequency of eating various dietary components such fruits, vegetables, whole and refined grains, meat and seafood, sodium, fats and sugars.

Participants self-scored their beginning and ending diet quality to determine their perceived scores. Their scores were also on a 0-100 scale based on the components of the HEI.

The self-assessment of their beginning diet was a “look back” as they scored both their starting and ending diets at the end of the study.

The difference in their starting and ending score was their perceived diet change.

The results

At the end of the study, only one in four participants accurately assessed the healthiness of their diet – in terms with how it matched with the researcher-assessed score.

The remaining three out of four participants believe they’d done significantly better than the HEI score assigned by researchers.

Where the participants, on average, perceived score was 67.6, the average HEI score was 56.4.

In judging the change in their diet over 12 months, only one in 10 participants perceived – that they’d made little to no real progress in terms of improving their diet.

Overall, after a year, the participants improved their diet quality by 1-2 points based on the researcher-assessed score.

Most participants’ perceived that they’d improved an average 18 points.

It seems that despite keeping a daily record of what they ate, most participants had no real understanding of what it actually meant in terms of diet quality.

Study author Dr Jessica Cheng is a postdoctoral research fellow in epidemiology at the Harvard T. H. Chan School of Public Health and in general internal medicine at Massachusetts General Hospital, both in Boston. The research was conducted while Dr Cheng was a predoctoral fellow in the department of epidemiology at the University of Pittsburgh School of Public Health.

“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,” She said.

It’s a disturbing finding given the mountains of dietary advice available online.

Perhaps the truth is that most people, when looking to lose weight, can’t be bothered doing the research or putting together a plan – and choose to wing it.

And winging it doesn’t work.