Evaluating CMR

Indices of Total Adiposity - BMI

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Table: BMI categories for classifying normal weight, overweight and obesity in Caucasians

Table: BMI categories for classifying normal weight, overweight and obesity in Caucasians

BMI and health risk
There is a large body of evidence to suggest that excess body weight as measured by BMI can have a number of harmful health effects, such as increasing risk of cardiovascular disease, type 2 diabetes, and mortality (1-8). However, BMI’s usefulness in predicting health risk beyond that of waist circumference alone is unclear (2, 3, 7-11). Though some studies have reported that BMI can help identify individuals at increased health and mortality risk beyond that of waist circumference alone (2, 3, 7, 8), others have not (2, 9-11).

Health-related BMI cut-offs
Health Canada and the National Institutes of Health (NIH) in the United States have developed BMI categories for classifying underweight, normal weight, overweight, and obesity in Caucasians (Table) (12, 13). These cut-offs appear to be appropriate for non-Hispanic blacks, but are likely too high for some Asian populations (8, 14-16). Appropriate BMI cut-offs for Asian populations are not as well established, but the suggested values for overweight range from 22 to 27 kg/m² and 26 to 31 kg/m² for obesity (14). These Asian cut-offs were based on the relationship between BMI and total adiposity in Asian versus Caucasian populations and did not consider the relationship of BMI to morbidity or mortality. Asians have more body fat than Caucasians for a given BMI, and the lower proposed BMI cut-offs for Asians reflect BMI values associated with the same percent body fat indicating overweight and obesity in Caucasian populations (14). For example, a BMI of 25 kg/m² in Caucasian populations generally means 22% body fat in men and 35% body fat in women. In contrast, individuals from Singapore will have this degree of body fatness with a BMI of only 22 kg/m². Some Asian populations also appears to be at increased health risk at lower BMI values compared to Caucasians. However, it is currently unclear whether ethnicity alters the association between BMI and health risk enough to warrant multiple population-specific BMI cut-offs.

Reference

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1. Folsom AR, Kushi LH, Anderson KE, et al. Associations of general and abdominal obesity with multiple health outcomes in older women: the Iowa Women's Health Study. Arch Intern Med 2000; 160: 2117-28.

2. Ho SC, Chen YM, Woo JL, et al. Association between simple anthropometric indices and cardiovascular risk factors. Int J Obes Relat Metab Disord 2001; 25: 1689-97.

3. Bigaard J, Tjonneland A, Thomsen BL, et al. Waist circumference, BMI, smoking, and mortality in middle-aged men and women. Obes Res 2003; 11: 895-903.

4. Allison DB, Zhu SK, Plankey M, et al. Differential associations of body mass index and adiposity with all-cause mortality among men in the first and second National Health and Nutrition Examination Surveys (NHANES I and NHANES II) follow-up studies. Int J Obes Relat Metab Disord 2002; 26: 410-6.

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6. Wang Z and Hoy WE. Waist circumference, body mass index, hip circumference and waist-to-hip ratio as predictors of cardiovascular disease in Aboriginal people. Eur J Clin Nutr 2004; 58: 888-93.

7. Farin HM, Abbasi F and Reaven GM. Body mass index and waist circumference both contribute to differences in insulin-mediated glucose disposal in nondiabetic adults. Am J Clin Nutr 2006; 83: 47-51.

8. Wildman RP, Gu D, Reynolds K, et al. Are waist circumference and body mass index independently associated with cardiovascular disease risk in Chinese adults? Am J Clin Nutr 2005; 82: 1195-202.

9. Janssen I, Katzmarzyk PT and Ross R. Body mass index, waist circumference, and health risk: evidence in support of current National Institutes of Health guidelines. Arch Intern Med 2002; 162: 2074-9.

10. Karter AJ, D'Agostino RB, Jr., Mayer-Davis EJ, et al. Abdominal obesity predicts declining insulin sensitivity in non-obese normoglycaemics: the Insulin Resistance Atherosclerosis Study (IRAS). Diabetes Obes Metab 2005; 7: 230-8.

11. Janssen I, Katzmarzyk PT and Ross R. Waist circumference and not body mass index explains obesity-related health risk. Am J Clin Nutr 2004; 79: 379-84.

12. Lau DC, Douketis JD, Morrison KM, et al. 2006 Canadian clinical practice guidelines on the management and prevention of obesity in adults and children. CMAJ 2007; 176: S1-117.

13. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults--The Evidence Report. National Institutes of Health. Obes Res 1998; 6 Suppl 2: 51S-209S.

14. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet 2004; 363: 157-63.

15. Deurenberg-Yap M and Deurenberg P. Is a re-evaluation of WHO body mass index cut-off values needed? The case of Asians in Singapore. Nutr Rev 2003; 61: S80-7.

16. Dalton M, Cameron AJ, Zimmet PZ, et al. Waist circumference, waist-hip ratio and body mass index and their correlation with cardiovascular disease risk factors in Australian adults. J Intern Med 2003; 254: 555-63.

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