Background: Overweight and obesity are an increasingly serious public health problem in Western societies, including Germany. The tendency of overweight and obese people not to classify themselves as such limits the efficacy of information on the health risks of these conditions and lessens the motivation to change behavior accordingly. In this article, we summarize the available study data on the selfperception of weight class. We present and discuss the differences between selfreported body-mass index (BMI) category and the actual category of the BMI when it is calculated from the individual's measured height and weight.
Methods: We systematically searched the Medline, EMBASE, and Cochrane Library databases in August 2017 for pertinent publications. The study protocol was published in the PROSPERO register (CRD42017064230). Meta-analyses were calculable for a number of subgroup analyses.
Results: A total of 50 studies from 25 countries were identified that contained findings on self-estimation of weight in a total of 173 971 study participants. The percentage of correct self-categorizations of BMI category varied from 16% to 83%, with marked heterogeneity of the population groups studied. In Europe, women overestimated their BMI category three times as often as men (RR: 3.22; 95% confidence interval: [2.87; 3.62], I2 = 0%). Most erroneous classifications were based on underestimates. Study participants of normal weight were more likely than others to categorize their BMI correctly. In European studies, 50.3-75.8% categorized their BMI correctly. Low socioeconomic status was associated with an incorrect perception of BMI.
Conclusion: The self-assignment of BMI categories is often erroneous, with underestimates being more common than overestimates. Physicians should take particular care to provide appropriate information to persons belonging to groups in which underestimating one's BMI is common, such as overweight people and men in general.