Are Some Bodies Resistant to BMI Hikes?

About three-quarters of men and two-thirds of women appear to be "resistant" to increasing body mass index (BMI), according to a study released Tuesday.

British researchers explained why, in some Western countries, the trend toward increasing BMI has slowed, according to Andrew Renehan, MBBCh, PhD of the University of Manchester. Their findings suggest that targeted approaches to reducing obesity might be more effective than population wide-interventions.

Their study which was published in the International Journal of Obesity used a mixture modeling method, which can identify subpopulations within an overall population, to analyze BMI data collected by the annual cross-sectional Health Surveys for England from 1992 and 2010.

Health survey data included BMI information on 164,166 adults, including 76,382 men and 87,773 women, ages 20 through 74. The investigators found that the median BMI for men rose from 25.6 kg/m2 in 1992 to 27.5kg/m2 in 2010. Similarly, it rose from 24.5kg/m2 in 1992 to 26.5kg/m2 in 2010 among women.

However, a splines analysis regression analysis showed that 2001 was a pivot year. Before then, median BMI was rising annually at about 0.140 and 0.139 25kg/m2 for men and women, respectively. After 2001, the increases were much smaller - 0.038 and 0.055 25 kg/m2 for men and women, respectively.

The researchers cautioned that the surveys captured BMI data for only about 63% of participants, raising the possibility of response bias. They also noted that the study does not have a true longitudinal cohort, but rather modeling was based on panel data of different individuals every year.

Prevalence of obesity also showed "significant variation by ethnicity" but the study population of the researchers was almost entirely Caucasian.