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Over the past decade, obesity rates have continued to rise among U.S. adults, researchers said.

Since 2007-2008, the prevalence of obesity significantly rose overall among adults, from 33.7% (95% CI 31.5%-36.1%) to 39.6% (95% CI 36.1%-43.1%) in 2015-2016 (P=0.001), reported Craig Hales, MD, of the National Center for Health Statistics of the Centers for Disease Control and Prevention in Hyattsville, MD, and colleagues.

Drawing upon data from the National Health and Nutrition Examination Survey, the study, published as a research letter in the , found that the prevalence of obesity -- defined as a body mass index (BMI) ≥30 -- between these years significantly rose across all age ranges and sexes (P≤0.05 for all). The results were as follows:

• Men: 32.2% to 37.9%
• Women: 35.4% to 41.1%
• Ages 20-39: 30.7% to 35.7%
• Ages 40-59: 36.2% to 42.8%
• Ages ≥60: 35.1% to 41.0%

Alarmingly, severe obesity among U.S. adults -- defined as a BMI ≥40 -- also significantly increased overall in adults from around 5.7% (95% CI 4.9%-6.7%) to 7.7% (95% CI 6.6%-8.9%) between 2007-2008 to 2015-2016 (P=0.001). All sexes and age groups individually had these increases, as well, except for those age 60 and older (P≤0.05 for all):

• Men: 4.2% to 5.6%
• Women: 7.3% to 9.7%
• Ages 20-39: 5.9% to 7.8%
• Ages 40-59: 6.4% to 8.5%

Rising obesity trends among U.S. youth were not quite as steep compared with adults, although no groups had any major increases in obesity or severe obesity prevalence within this time period. For youth, obesity was defined as a BMI ≥95th percentile, while severe obesity was considered a BMI ≥120% of the 95th percentile.

However, youth between the ages of 2 and 19 did show an overall trend towards a slight increase in obesity prevalence, rising from 16.8% (95% CI 14.2%-19.8%) to 18.5% (95% 15.8%-21.3%). Although it did not reach significance, most groups saw a slight increase in obesity prevalence during this time, except for the age group of 6 to 11, which had a slight decrease of 19.6% to 18.4%:

• Boys: 17.7% to 19.1%
• Girls: 15.9% to 17.8%
• Ages 2-5: 10.1%to 13.9%
• Ages 12-19: 18.1% to 20.6%

Similar trends were reported among youth with severe obesity, with a slight decrease seen in the age 6-to-11 group (5.7% to 5.2%) and a plateau among the age 2-to-5 group (1.8% to 1.8%). Other groups saw only a slight trend towards a rise in severe obesity prevalence:

• Boys: 5.5% to 6.3%
• Girls: 4.3% to 4.9%
• Ages 12-19: 5.9% to 7.7%

The researchers did not offer an explanation as to why obesity prevalence has risen only among U.S. adults, stating just that "changes in demographics did not explain the observed trends." The team did, however, note that the sample sizes among the age 2-to-5 group were small, which may have limited the findings.

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