Why are BMIs Useful?

BMI is a simple, inexpensive screening tool used to identify possible weight problems for both adults and children. A BMI measurement is useful to assess who needs further testing to identify health risks, such as heart disease . Individuals at risk will need further assessment. Assessments may include skin fold thickness test, diet, physical activity level, family history, and other appropriate health screenings.

What are the Risks Associated with Having an Extreme BMI?

Being either overweight (with BMI of 25 or above) or underweight (with BMI lower than 18.5) can affect your health.

Risks of Being Overweight: Being overweight increases your chances of developing diseases. An overweight individual whose BMI rises from 25 to 27 is 20-30% more at risk of premature death. As an individual’s BMI rises above 27, the risk of death increases more steeply-by almost 60%. If you are overweight and have low physical activity, the risk of developing diseases increases. Listed below is a list of diseases associated with being overweight.

• Gastrointestinal disorders
• Cardiovascular diseases: stroke, heart attack
• Diabetes
• High blood pressure (Hypertension)
• Osteoarthritis
• Infertility
• Some forms of cancer: breast, colon and endometrial cancers
• Menstrual abnormalities
• Gall bladder disease
• Sleep problems: obstructive sleep apnoea
• Respiratory problems: asthma

Risks of Being Underweight: If you are underweight you may be malnourished, and in addition, you may develop the following nutritional deficiencies:

• Compromised immune function with increased susceptibility to infections
• Respiratory diseases
• Digestive diseases
• Cancer
• Osteoporosis ( weakening of the bones)
• Increased risk of falls and fractures

What are the Limitations of BMI?

Listed below are limitations associated with BMI:

• BMI varies by age, sex and race, hence one’s BMI can only be compared to those of same sex, age and race.
• BMI does not differentiate between muscle and fat and will, therefore, underestimate in some and overestimate for others: For example, an athlete may have a high BMI because of greater amount of muscle rather than fat.
• Disabled or elderly people have less muscle mass and therefore will have a lower BMI. This does not necessarily mean that their BMI is normal or underweight.
• Pregnant women will also have a higher BMI because of increased weight associated with pregnancy but not necessarily due to increased fat and hence BMI will overestimate body fat in this case.
• BMI does not differentiate between body fat distribution and, since fat around the waist (“apple” body shape) is more dangerous than that around the hips (“pear” body shape), this will not be picked up by BMI.
• Do consult your health care giver for other physical measures that may need to be used along with BMI for assessing health risks associated with obesity.

Reference

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11. Mukuddem-Petersen J, Snijder MB, van Dam RM, Dekker JM, Bouter LM, Stehouwer CDA, et al. Sagittal abdominal diameter: no advantage compared with other anthropometric measures as a correlate of components of the metabolic syndrome in elderly from the Hoorn Study. Am J Clin Nutr 2006 [cited November 1, 2006];84(5):995-1002. Available from: www.ajcn.org/cgi/content/abstract/84/5/995
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13. Esmailzadeh A, Mirmiran P, Azizi F. waist-hip ratio is a better screening measure for cardiovascular risk factors than other anthropometric indicators in Tehrannian adult men. Intntl J. of Obesity 2004;28:1325-1332.
14. NHMRC. Clinical Practice Guidelines for the Management of Overweight and Obesity in Adults; 2003. Available from http://www.health.gov.au/internet/main/publishing.nsf/Content/obesityguidelines-guidelines-adults.htm

*Disclaimer: Results may vary for each person.