Are teens confused about their size and weight?

"Third of overweight teenagers think they are right size, study shows," The Guardian says in one of many headlines on widely covered English research.

The research, which looked into English 13-15-year-olds' understanding of their own weight, led the Mail Online to refer unkindly to "generation fat-blind".

The large study demonstrated that while most normal-weight adolescents correctly see themselves as about the right weight, a large number of overweight or obese adolescents wrongly thought they were about the right weight or too light.

Parents probably ought to refrain from a "told you so" attitude to this news, as so-called fat shaming is not considered a great way to help anyone lose weight.

Helping a teen to understand that familiar media images of overweight and obese people don't necessarily give the full picture, and that addressing the problem can improve the quality and length of their life, may be more successful.

The findings may also help policymakers work out how best to target health promotion messages at this important age group and help them potentially make changes for the rest of their lives. 

Where did the story come from?

The study was carried out by researchers from University College London and was funded by Cancer Research UK.

It was published on an open-access basis in the peer-reviewed International Journal of Obesity.

This study was accurately reported by a number of media sources, with a good explanation of its key findings and the risks associated with obesity.

However, there was a general lack of information about the limitations of this study. The Mail's headline use of the term "fat-blind" may be seen as pejorative and misleading, especially when we do not necessarily understand all the reasons for the research findings. 

What kind of research was this?

This study analysed data from the Health Survey for England looking at adolescents' perception of their weight.

Looking at this data is a good way to understand adolescents' weight perceptions because measurements were taken professionally and weight perception questions were self-reported in the survey.

However, this type of study can have chunks of missing data, particularly where people declined to be weighed, which may have biased the results. 

What did the research involve?

The researchers used data for 4,979 teens aged 13 to 15. The data was taken from the results of the Health Survey for England between 2005 and 2012.

This annual survey presents a representative sample of the general population of England. It surveys adults and up to two children under 16 (selected at random in families with three or more eligible children).

Researchers weighed and measured the teens at home, and then calculated their body mass index (BMI). Weight status was defined according to the International Obesity Taskforce criteria, which classifies BMI values according to age and sex as:

  • thin (underweight)
  • normal weight
  • overweight
  • obese

The 13-15-year-olds were also asked: "Given your age and height, would you say that you are about the right weight, too heavy, or too light?".

The researchers also included age, sex, ethnicity and the socioeconomic status of the teens in their analyses. 

What were the basic results?

The data showed nearly three-quarters (73%) of adolescents in the study had a BMI placing them in the normal weight range, but 20% were overweight and 7% were obese.

Normal-weight adolescents generally felt they were the correct weight (83%), with just 7% who thought they were too heavy, while 10% thought they were too light.

More girls (11%) considered themselves too heavy than boys (4%). Girls (6%) were also less likely to consider themselves too light than boys (13%).

Overestimation was more likely among those on the heavier end of the normal-weight group (10%) than the lighter end (2%).

About 60% of the overweight/obese group felt they were too heavy, 39% thought they were about the right weight, and 0.4% felt they were too light.

Again, girls (68%) who were overweight or obese were more likely to think so than boys (53%).

Girls (32%) were also less likely than boys (47%) to think they were the right weight or too light. Overweight adolescents were much more likely to underestimate their weight (52%) than those who were obese (7%).

The researchers excluded adolescents who were underweight from the analysis as this group consisted of 248 people, which they say was too small to calculate meaningful results. 

How did the researchers interpret the results?

The researchers concluded that, "Overestimation of body weight among normal-weight adolescents is relatively uncommon; potentially a cause for celebration.

"However, almost half of boys and a third of girls with a BMI placing them in the overweight or obese BMI range perceived themselves to be about the right weight.

"Lack of awareness of excess weight among overweight and obese adolescents could be cause for concern." 


This study aimed to see whether English teenagers' perception of their weight matched up with reality. It demonstrated that most normal-weight adolescents correctly see themselves as about the right weight and they overestimated their weight fairly rarely.

But a large proportion of overweight and obese adolescents thought they were about the right weight or even too light.

This study had a large population size, and analyses were weighted to match key population characteristics.

However, the weight measurements were not available for all adolescents in the survey – this may have represented those who were more concerned about their weight and declined measurement, leading to biased results.

Also, overweight and obese adolescents may not have completed the questionnaires truthfully through embarrassment or fear of the consequences.

Only people aged 13 to 15 were analysed, so further research would need to be carried out in other age groups to target issues associated with weight perception if necessary.

Overweight and underweight teens are a concern to both their parents and society. They are likely to grow into overweight or underweight adults, particularly if they do not see that they are not a healthy weight.

The reasons teenagers don't see themselves as overweight may include the commonly seen images of severely obese individuals in the media used to represent stories about weight issues. These could lead to the impression that only those who have a visibly very high body weight are overweight or obese.

Excess weight can lead to a range of other health concerns, including an increased risk of type two diabetes and certain cancers.

Even if teenagers aren't interested in these long-term health messages, it's vital to find ways to improve their understanding of the implications of their weight. And if they understand, it's vital we're able to give them simple advice on achieving a healthy weight in a way that doesn't make them feel patronised.

NHS Attribution