Risk and Protective Factors

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Risk and Protective Factors > Body weight

Body mass index (BMI) provides a useful population-level indicator of excess body weight. It is a measure of weight adjusted for height, and is calculated by dividing weight in kilograms by the square of height in metres (kg/m2).

Higher BMI cut-offs were used to classify overweight and obesity in Māori and Paciﬁc peoples (Swinburn 1998), due to different body composition, as given in Table 10. For example, obesity is deﬁned as a BMI of ≥ 32 for Māori and Paciﬁc peoples, compared to ≥ 30 for European and Other. However, it is acknowledged that ethnic-speciﬁc cut-offs are controversial (WHO Expert Consultation 2004).

Table 10: Classification of body weight according to BMI (kg/m2) in adults

Classification	European and Other	Māori and Pacfic peoples
Underweight	< 18.5	< 18.5
Overweight	25.0-29.9	26.0-31.9
Obese	> 30.0	> 32.0

Details on the classiﬁcation of overweight and obesity in children can be found in Cole et al (2000).

The association between BMI and health risk is continuous (Asia Paciﬁc Cohort Studies Collaboration 2004), and therefore it is useful to have some information about the BMI distribution, rather than relying on BMI cut-offs alone. For this reason, this report presents data on BMI percentiles, as well as underweight, overweight and obesity. For example, a 10th percentile BMI of 22 means that 10 percent of the population have a BMI of 22 or less; a 50th percentile BMI of 28 means that 50 percent of the population have a BMI of 28 or less.

Table 11: Body weight indicators

How to interpret results - tables

Indicator	Māori			non-Māori
Indicator	Males	Females	Total	Males	Females	Total
Overweight, 5-14 years, 2002, percent ^{1,2 *}	19.8 (16.8-22.7)	30.5 (26.4-34.6)	25.0 (22.6-27.5)	20.2 (17.3-23.2)	20.4 (17.0-23.7)	20.3 (18.1-22.4)
Obese, 5-14 years, 2002, percent	15.7 (11.9-19.6)	16.8 (13.1-20.6)	16.2 (13.1-19.3)	7.1 (5.3-8.9)	8.8 (6.5-11.1)	7.9 (6.5-9.3)
BMI 10th percentile 5-14 years, 2002, BMI value ^{1,2 *}	15.7 (15.5-16.0)	15.8 (15.6-16.0)	15.8 (15.7-16.0)	15.3 (15-15.6)	15.3 (15.1-15.5)	15.3 (15.1-15.3)
BMI 50th percentile, 5-14 years, 2002, BMI value ^{1,2 *}	18.6 (18.3-19)	19.4 (18.9-19.9)	18.9 (18.7-19.2)	17.8 (17.6-18.1)	18.2 (17.9-18.5)	18.0 (17.8-18.2)
BMI 90th percentile 5-14 years old, 2002, BMI value, ^{1,2 *}	25.1 (23.8-26.4)	27.0 (25.4-28.6)	26.2 (24.9-27.5)	23.7 (23.1-24.4)	24.1 (23.2-25.0)	24.0 (23.6-24.4)
Underweight, 15+ years, 2002/03 percent ^{1,2 **}	-	2.7 (0.8-4.7)	1.3 (0.5-2.1)	3.0 (2.0-4.0)	4.6 (3.5-5.7)	3.8 (3.1-4.5)
Overweight, 15+ years, 2002/2003, percent ^{1,2 **}	37.2 (31.9-42.4)	31.1 (26.4-35.9)	34.3 (31.3-37.2)	39.2 (36.9-41.6)	25.2 (23.3-27.2)	32.2 (30.8-33.7)
Obese, 15+years, 2002/03, percent ^{1,2 **}	26.5 (21.5-31.4)	26.1 (21.8-30.3)	27.0 (23.8-30.3)	16.9 (15.3-18.5)	19.1 (17.5-20.8)	18.0 (16.8-19.1)
BMI 10th percentile, 15+ years, 2002/03, BMI value ^{1,2 **}	22.1 (21.5-22.6)	20.8 (20.0-21.7)	21.6 (21.2-21.9)	20.6 (20.1-21.0)	19.6 (19.4-19.8)	20.0 (19.9-20.2)
BMI 50th percentile, 15+ years, 2002/03, BMI value ^{1,2 **}	28.1 (27.1-29.1)	27.9 (26.9-28.8)	27.9 (27.2-28.7)	25.7 (25.4-26.0)	24.2 (23.9-24.5)	25.1 (24.9-25.3)
BMI 90th percentile, 15+ years, 2002/03, BMI value ^{1,2 **}	37.9 (35.9-39.8)	37.8 (35.6-39.9)	37.9 (36.6-39.1)	32.1 (31.7-32.5)	33.4 (32.8-34.0)	32.7 (32.4-33.0)

Sources: ^* 2002 Children's Nutrition Survey, ^** 2002/2003 New Zealand Health Survey

For children, Māori and non-Māori males had a similar prevalence of overweight, but Māori females were one-and-a-half times more likely to be overweight than non-Māori females (RR 1.5, CI 1.2–1.8). Overall, the prevalence of obesity in Māori children was twice that of non-Māori children (RR 2.0, CI 1.5–2.6). Both the BMI 10th and 50th percentiles for Māori and non-Māori children were similar, although Māori children had a higher BMI 90th percentile.

Māori and non-Māori adults had a similar prevalence of overweight, but Māori adults were one-and-a-half times more likely to be obese than non-Māori (RR 1.5, CI 1.3–1.7). Māori adults were signiﬁcantly less likely to be underweight than non-Māori adults (RR 0.3, CI 0.1–0.5), and Māori adults had higher 10th, 50th and 90th percentiles for BMI than non-Māori adults.

Notes:
¹ Age-standardised to 2001 Census total Māori population.
² Prioritised Maori ethnic group - see Methods and Data Sources section for further information.
³ Indicates that the count was < 5 and therefore the age-standardised rate was not calculated.

References:
Swinburn B. 1998. Using the body mass index: weigh then weigh up. New Zealand Medical Journal 111: 377-9.
WHO Expert Consultation. 2004. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 363: 157-63.
Asia Pacific Cohort Studies Collaboration. 2004. Body mass index and cardiovascular disease in the Asia-Pacific Region: an overview of 33 cohorts involving 310,000 participants. International Journal of Epidemiology 33: 751-8.
Cole TJ, Bellizzi MC, Flegal KM, et al. 2000. Establishing a standard definition for child overweight and obesity worldwide: international survey. British Medical Journal 320: 1-6.

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