Official confirmation. Age 18 BMI cutoffs of Body Mass Index were applied to all adults as overweight and obesity criteria.

The full text of this article is available free at British Medical Journal online.

The authors found 6 diverse nations having good data about body mass index in children. It averaged all their data to create a composite "international" set of curves defining "overweight" and "obese". The curves were designed to reach a BMI of 25 (overweight) or 30 (obese) at age 18. Why?

"A workshop organised by the International Obesity Task Force proposed that these adult cut off points be linked to body mass index centiles for children to provide child cut off points.^1,2 We describe the development of age and sex specific cut off points for body mass index for overweight and obesity in children, using dataset specific centiles linked to adult cut off points."

"Each centile curve defines cut off points through childhood that correspond in prevalence of overweight or obesity to that of the adult cut off point the curve joins up points where the prevalence matches that seen at age 18."

I was looking for a reference stating that the WHO criteria for overweight at BMI=25, was based on young adults, and this article specifically confirms that Age=18 was used.

This makes it easier for me to disagree with applying BMI=25 as an overweight criteria for all adult ages. I just don’t think an 18-year old’s body composition is a realistic standard for middle-aged or elderly adults to aspire to.

 

Age (years)	"Overweight" is a BMI greater than:			"Obese" is a BMI greater than:
	Boys	Girls		Boys	Girls
2	18.41	18.02		20.09	19.81
2.5	18.13	17.76		19.80	19.55
3	17.89	17.56		19.57	19.36
3.5	17.69	17.40		19.39	19.23
4	17.55	17.28		19.29	19.15
4.5	17.47	17.19		19.26	19.12
5	17.42	17.15		19.30	19.17
5.5	17.45	17.20		19.47	19.34
6	17.55	17.34		19.78	19.65
6.5	17.71	17.53		20.23	20.08
7	17.92	17.75		20.63	20.51
7.5	18.16	18.03		21.09	21.01
8	18.44	18.35		21.60	21.57
8.5	18.76	18.69		22.17	22.18
9	19.10	19.07		22.77	22.81
9.5	19.46	19.45		23.39	23.46
10	19.84	19.86		24.00	24.11
10.5	20.20	20.29		24.57	24.77
11	20.55	20.74		25.10	25.42
11.5	20.89	21.20		25.58	26.05
12	21.22	21.68		26.02	26.67
12.5	21.56	22.14		26.43	27.24
13	21.91	22.58		26.84	27.76
13.5	22.27	22.98		27.25	28.20
14	22.62	23.34		27.63	28.57
14.5	22.96	23.66		27.98	28.87
15	23.29	23.94		28.30	29.11
15.5	23.60	24.17		28.60	29.29
16	23.90	24.37		28.88	29.43
16.5	24.19	24.54		29.14	29.56
17	24.46	24.70		29.41	29.69
17.5	24.73	24.85		29.70	29.84
18	25	25		30	30

This table above, contains the main data from this article. The data is graphed in the chart below, labelled as the "International" blue line, compared to the 85^th and 95^th percentiles from the CDC growth charts.

You can see that International and CDC growth charts definitions of "Overweight" are very similar. I like the international definition slightly better, because of the way it curves downward near age 18. This helps make a more natural transition to a BMI of 25 for adults over age 18.

The "Obesity" criteria are different however, with the International criteria being higher than the CDC growth charts. The explanation may be that the CDC growth charts are based on a mix of newer and older American data. Older data has less fatness, resulting in a lower line on the chart. I like the International criteria a little better.

Try the Body Mass Index calculator for men calculator, or the BMI calculator for women.

 
 

Update in 2014. A link to a different article with similar evidence of using age 18 BMI for all adults.

References

1. Dietz WH, Robinson TN. Use of the body mass index (BMI) as a measure of overweight in children and adolescents. J Pediatr 1998; 132: 191-193
2. Bellizzi MC, Dietz WH. Workshop on childhood obesity: summary of the discussion. Am J Clin Nutr 1999; 70: 173-15S.
3. Maynard LM, Wisemandle W, et al. Childhood body composition in relation to body mass index. Pediatrics 2001;107:344-50.

 
 

Links to related references on my website: The childhood definition of overweight.