The study is published in the December issue of Obstetrics & Gynecology, and is the work of lead author Dr Mahbubur Rahman, Assistant Professor in the Department of Obstetrics & Gynecology at the University of Texas Medical Branch (UTMB) in Galveston, and Dr Abbey Berenson, Professor of Obstetrics and Gynecology and Pediatrics Chief in the UTMB Division of Pediatric and Adolescent Gynecology.
While the study only included low-income women attending publicly funded clinics in Texas, it does reflect findings of studies of other groups, reports HealthDay news.
For their research, Rahman and Berenson assessed "perceptions of body weight and weight-related behaviors" among 2,224 women attending one of five publicly funded reproductive clinics in Texas between August 2008 and March 2010.
The women, who were aged between 18 and 25, had filled in questionnaires that had asked them about their health behaviors and how they perceived their body weight, and Rahman and Berenson were able to compare the women's responses with "actual" measurements from their medical records at the clinic.
The researchers used the standard BMI definition of normal (18.5 - 24.9), overweight (25 - 29.9) and obese (30 and over). (BMI stands for body mass index, which is the ratio of a person's weight in kilos to the square of their height in metres).
Based on the women's questionnaire responses about how they perceived their body weight compared to their measured body weight, Rahman and Berenson divided the results into four categories:
- Overweight misperceivers: these were women whose actual BMI classed them as overweight but according to their questionnaire responses saw themselves as being normal weight.
- Overweight actual perceivers: women who were actually overweight and also saw themselves as such.
- Normal weight misperceivers: women who were normal weight but saw themselves as overweight.
- Normal weight actual perceivers: women who were normal weight and saw themselves as normal or underweight.
Also, among the overweight women, the African-Americans were the most likely to see themselves as normal weight (28% compared with 25% of Hispanics and 15% of whites).
In contrast, among the 1,062 (48%) of women who were of normal weight, 16% were misperceivers: that is they considered themselves to be overweight, and in this group, the African-American women were less likely than whites to see themselves as overweight (7% compared with 16%).
Rahman and Berenson also found that women who had some college education were less likely to misperceive their body weight, as were those who used the Internet.
When they looked at what the women reported about their health behaviors in the previous three months, the researchers found that ones most likely to report healthy and unhealthy (eg taking diet pills and diuretics) attempts to reduce weight were normal weight women who considered themselves overweight (compared to normal weight women who accurately saw themselves as of normal weight).
In contrast, they found the opposite results for overweight women who considered themselves to be normal weight: that is they were less likely to have tried losing weight.
Rahman and Berenson concluded that:
"Weight misperception is common among both overweight and normal-weight women of reproductive age."
They suggested doctors should take into account how their patients perceive their weight when giving them advice about weight management.
Some experts suggest this study shows the importance of correctly monitoring one's weight, for the obvious reason that if we think we are not overweight when we are, then we are less likely to do something about it.
Keri Gans, spokeswoman for the American Dietetic Association said if women "don't perceive themselves as overweight, they're not going to adopt healthy behaviors to lose weight and prevent disease".
Gans, who is a registered dietician, told HealthDay that women of normal weight who consider themselves overweight might also be in danger of making themselves ill if they try to lose weight unnecessarily.
She said all women need to be aware of "normal" weight, and to monitor creeping weight gain not just by regular weighing but also by being aware of other signs, such as when clothes start feeling tight.
Rahman thinks their finding that so many overweight women now regard themselves as being of normal weight reflects the rising obesity crisis in America.
"They see overweight people everywhere they go," he said, and this has become the new norm for them.
He told WebMD that he is worried the trend will just go on unless there is a "rapid change in the mind-set of people".
"Self-Perception of Weight and Its Association With Weight-Related Behaviors in Young, Reproductive-Aged Women."
Mahbubur Rahman, Abbey B. Berenson.
Obstetrics & Gynecology. 116(6):1274-1280, December 2010.
Additional sources: HealthDay, WebMD.