Do the obese know they are obese?

Apr 16 2006

Obese men and women are reasonably accurate when it comes to reporting their own weight, says researchers, but they are much more likely than normal weight persons to misjudge what weight falls into the obese category and therefore do not consider themselves to be obese.

Dr. Kimberly Truesdale, a research associate in the laboratory of Dr. June Stevens, University of North Carolina at Chapel Hill, presented the study at Experimental Biology 2006 in San Francisco. The presentation was part of the scientific program of the American Society of Nutrition, Inc.

One hundred and four men and women, both white and African American, between the ages of 45 to 64, were asked to report their weight in pounds; categorize themselves as either underweight, normal weight, overweight, or obese; and estimate how much they would need to weigh in order to be considered obese. The researchers then collected weight, height, and other measures for each person. BMI, or body mass index was calculated by weight in kilograms divided by height in meters squared: a standard tool for categorizing individuals as either normal weight (BMI: 18.5 - 24.9 kg/m squared); overweight (25.0 - 29.9 kg/m squared) or obese BMI: greater than 30.0 kg/m squared).

Using the measured BMI, there were 31 normal weight, 40 overweight, and 33 obese adults in the group. About 90 percent of normal weight adults and 85 percent of overweight and obese adults accurately self-reported their weight and height such that the BMI calculated using those self reports fell in the same category as actual BMI.

That accuracy changed, however, when researchers asked participants about their perceived weight status, that is, if they would consider themselves NOW to be underweight, normal weight, overweight, or obese. Seventy-one percent of normal weight and seventy-three percent of overweight adults classified themselves correctly, compared to only 15 percent of obese adults who correctly considered themselves to be obese.

The researcher then asked participants how much they would need to weigh to be classified as either underweight, normal weight, overweight, or obese, and again the results varied depending on current weight status. On average, normal weight participants were reasonably accurate in these estimates, but obese participants overstated how much they could weight for every weight status category, from underweight to obese. For example, if a participant was 5;7" and normal weight, they would estimate normal weight as 143 pounds (BMI = 22.4 kg/m squared) and obesity as 189 pounds (BMI = 29.6 kg/m squared) but an obese participant the same height would estimate normal weight as 164 pounds (BMI = 25.7 kg/m squared) and obesity as 233 pounds (BMI - 36.5 kg/m squared.)

These findings have important public health implications, say Dr. Truesdale and Dr. Stevens. If obese adults do not consider themselves to be obese, they are not likely to pay full attention to public health messages about the consequences of being obese. More research is needed into why obese adults do not consider themselves to be obese, with two possibilities being perception and denial.