To compare changes over time in waist circumference (a measure of central fatness) and body mass index (a measure of overall obesity) in British youth.
Representative cross sectional surveys in 1977, 1987, and 1997.
Young people aged 11-16 years surveyed in 1977 (boys) and 1987 (girls) for the British Standards Institute (n=3784) and in 1997 (both sexes) for the national diet and nutrition survey (n=776).
Main outcome measures
Waist circumference, expressed as a standard deviation score using the first survey as reference, and body mass index (weight(kg)/height(m)2), expressed as a standard deviation score against the British 1990 revised reference. Overweight and obesity were defined as the measurement exceeding the 91st and 98th centile, respectively.
Waist circumference increased sharply over the period between surveys (mean increases for boys and girls, 6.9 and 6.2 cm, or 0.84 and 1.02 SD score units, P<0.0001). In centile terms, waist circumference increased more in girls than in boys. Increases in body mass index were smaller and similar by sex (means 1.5 and 1.6, or 0.47 and 0.53 SD score units, P<0.0001). Waist circumference in 1997 exceeded the 91st centile in 28% (n=110) of boys and 38% (n=147) of girls (against 9% for both sexes in 1977-87, P<0.0001), whereas 14% (n=54) and 17% (n=68), respectively, exceeded the 98th centile (3% in 1977-87, P<0.0001). The corresponding rates for body mass index in 1997 were 21% (n=80) of boys and 17% (n=67) of girls exceeding the 91st centile (8% and 6% in 1977-87) and 10% (n=39) and 8% (n=32) exceeding the 98th centile (3% and 2% in 1977-87).
Trends in waist circumference during the past 10-20 years have greatly exceeded those in body mass index, particularly in girls, showing that body mass index is a poor proxy for central fatness. Body mass index has therefore systematically underestimated the prevalence of obesity in young people.
What is already known on this topic
The prevalence of overweight and obesity in youth based on body mass index has increased over the past 10-20 years
Body mass index gives no indication of body fat distribution
Waist circumference is a marker for central body fat accumulation; a large waist circumference is linked to an increased risk of metabolic complications
What this study adds
Waist circumference in British youth has increased over the past 10-20 years at a greater rate than body mass index, the increase being greatest in females
The accumulation of central body fat has risen more steeply than whole body fatness based on height and weight
Current and future morbidity in British youth may be seriously affected due to accumulation of excess central fat