The current study examined the accuracy of self-reported height and weight, perceived weight status category (underweight, normal weight, overweight or obese), and ability to recognize how much one would need to weigh in order to be classified in each weight status category. Our results showed that in general women and men tended to slightly underreport their weight and overreport their height, thus causing BMI to be slightly underreported. These findings are consistent with other studies.3–5,9
Using self-reported weight and height, the majority of subjects would have been categorized into the correct weight status category. In general, the magnitude of underreporting for obesity was greater among women than men (3.9 versus 1.9 percentage points). Similar patterns were found using data from the third National Health and Nutrition Examination Surveys (NHANES III), where the prevalence of obesity was underreported by 4.5 and 6.1 percentage points in White and African American women and 3.2 and 2.3 percentage points in White and African American men10
when they were categorized using BMI from self-reported height and weight.
We saw less accuracy when participants classified themselves into the weight status categories, and 40.4% of women and 51.9% of men misclassified their weight status category. Researchers wanting to classify adults into weight categories should ask participants to report their weight and height and use these data to construct weight status categories rather than asking participants to classify themselves into a category.
Perceptions of how much one needed to weigh in order to be classified in each weight status category varied by gender and measured weight status. Given our findings, a normal weight woman 64 inches (5 ft, 4 in) tall would estimate overweight to be 139 pounds (BMI=23.9 kg/m2) and obesity to be 168 pounds (BMI=28.9 kg/m2), whereas an obese woman of the same height would estimate 178 pounds (BMI=30.6 kg/m2) and 222 pounds (BMI=38.2 kg/m2), respectively. A normal weight man 70 inches (5 ft, 10 in) tall would estimate normal weight to be 164 pounds (BMI=23.5 kg/m2) and obesity to be 210 pounds (BMI=30.2 kg/m2), whereas an obese man of the same height would estimate 186 pounds (BMI=26.7 kg/m2) and 241 pounds (BMI=34.5 kg/m2), respectively.
Other investigators have examined how accurately adults can identify their weight status.11–14
Using data from the NHANES III study, Chang et al found moderate agreement between self-perceived and measured weight status (kappa=0.48 for women and 0.45 for men).11
Approximately 27.5% of women and 29.8% of men misclassified their weight status.11
The smaller percentage of weight status misclassification in the Chang et al study compared to the current study may have been due to the number of categories listed. In the current study, subjects were able to select from 4 weight status categories (underweight, normal weight, overweight, obese) as opposed to the 3 categories used in the NHANES III study.11
Australia’s 1995 National Health Survey and National Survey also used only 3 weight status categories (acceptable weight, underweight, overweight) and found less misclassification (28% of women and 50.7% of men)12
than found in the current study (40.4% of women and 51.9% of men). If we combined the overweight and obese categories in the current study, the misclassification percentage decreased to 15.4% in women and 30.8% in men and the kappa statistics increased in women (unweighted: 0.38 to 0.61, weighted: 0.45 to 0.61) and men (unweighted: 0.21 to 0.40, weighted: 0.31 to 0.43). This suggests that many women may not distinguish between overweight and obesity, whereas many men may not distinguish between normal weight and overweight.
Another possible explanation for the larger percentage of misclassification in the current study is the use of the term obese as one of the weight status categories. Wardle et al found that approximately 35% of men and women misclassified their weight status;13
however, the largest weight status category was referred to as very overweight instead of obese. In a study of Dutch men and women, Blokstra et al asked participants to describe their weight status as too fat, too thin, or just right.14
The majority of normal weight men (79.2%) and women (73.3%) considered their weight to be just right. In addition, the majority of obese men (91.4%) and women (97.2%) considered themselves to be too fat. The findings from these studies suggest that adults may be more reluctant to label themselves obese as opposed to very overweight or too fat.
Blokstra et al asked participants their ideal body weight and converted it to BMI units.14
The reported ideal BMI was higher among obese men and women (27.5 and 27.1 kg/m2
) compared to normal weight men and women (22.7 and 21.3 kg/m2
). Crawford et al asked participants, “Ideally, how much would you like to weigh at the moment?” and “In your opinion, what is the most you could weigh and still not consider yourself overweight?”15
Using measured heights 1 year prior, the weights were converted into BMI units. The BMIs considered ideal and overweight were 22.7 and 23.7 kg/m2
among women and 24.9 and 26.1 kg/m2
among men. Both estimates increased across measured weight status categories. This is similar to our finding that as weight status increased, the reported BMI cutpoints for each weight status category increased.
Whisenhunt et al asked women to report (given specified heights) the weight range for 6 weight categories (extremely underweight, underweight, normal weight, overweight, obese, and extremely obese).16
They found significant differences between normal weight and overweight participants in the lower and upper BMI cutpoints reported for normal weight, overweight, and obesity. For example, normal weight participants defined normal weight as 19.95 to 22.12 kg/m2
and obesity as 26.75 to 30.83 kg/m2
, whereas obese women defined these categories as 21.65 to 24.27 kg/m2
and 32.19 to 37.68 kg/m2
. In the current study we did not ask participants for a weight range, therefore it is plausible that differences between the categories could be due to normal weight participants reporting minimum weights and obese participants reporting maximum weights for each category.
Another potential reason for the lower percentage of obese women and men correctly identifying themselves could be their reluctance to report that they are obese to a health care researcher. However, it is important to note that the obese subjects self-reported their current weight and height with reasonable accuracy. The main discrepancy came when they had to put a label on their weight. The term obesity can have social associations such as negative bias, stigma, and discrimination.17
These associations may make adults more reluctant to label themselves as obese. In addition, images of obesity in popular media often show class II or III obesity (BMI≥35.0 kg/m2
). This could distort the perceived definition of obesity.
This study has limitations that should be considered when interpreting the findings. The study sample was composed of volunteers living in specific areas of North Carolina and was not selected to be representative of a population. Therefore caution must be used in the generalization of results. Another limitation was the small sample size. We were able to detect some differences by gender and race; however, more subtle trends may have been missed including bias associated with education or employment The study design resulted in unequal distribution of normal weight, overweight, and obese women and men in each race-gender group. It is possible that ethnic differences in attitudes toward weight could have influenced our findings, although we did not find any significant or suggestive race interactions. Other investigators have shown that African American women express a greater amount of body satisfaction and acceptance at higher BMI levels compared to White women.18–23
In addition, other studies have shown that African Americans tend to have lower rates of perceived overweight compared to Whites.24–27
Another limitation is that demographic variables (ie, marital status, education level) that have been shown to be associated with perceived weight status were not collected. Wardle et al found that adults in lower socioeconomic status classes were less likely (OR=0.57, 95% CI: 0.39 – 0.84) to perceive themselves as overweight compared to socioeconomic class 1 and 2 (higher social class).28
Paeratakul et al also found higher rates of self-perceived overweight in adults with higher education level (OR=1.6, 95% CI: 1.1–2.3) and higher income level (OR=1.5, 95% CI: 1.2–1.7).25
This study did not examine why obese women and men did not consider themselves to be obese. Possible reasons include skewed perception, denial, and reluctance to report obesity in a study setting.