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Reliability of Body Mass Index In Obesity Measurement

Drotumdi O

Otumdi Omekara thumbnail.jpg

Otumdi Omekara, MD. MPAHA, Member of Society of Physician Entrepreneurs

After many years of argument researchers have seemingly come to terms with the fact that an overweight person can also be metabolically healthy to the same extent that a normal weight person can be metabolically unhealthy (Jeffrey Hunter et al, 2016).

This paradigm change comes at a time when the US fashion industry has just started promoting plus-sized models to challenge the notion that being large-sized automatically means being unhealthy and being thin automatically means being healthy and beautiful.

The only problem with this government observational survey is that it is a relatively lower level research study, hardly usable for establishing causal relationships between any two variables. Higher level randomized clinical intervention studies still uphold body mass index BMI as the yard stick for measuring obesity alone, excluding overweight patients (Mora, IM Lee et al, 2006).

This same study also acknowledged an increased positve correlation between BMI and cardiovascular risk factors, after adjustment for physical activity. But the federal survey team did not factor that into their explanation for the higher sensitivity of metabolic risk factors alone.

High level research has also established that both overweight and underweight patients have higher cardiovascular, renal and endocrinological morbidity and mortality rates (Bleich S. et al, 2008 ; WHO, 2015).

As such, it ought not to be too surprising that the government survey found many (marginally) normal weight adults with abnormal metabolic risk marker results (high blood pressure, high blood glucose, high cholesterol and high c-reactive protein, etc.). Even more so, it should not be the basis for downplaying the role of BMI as the gold standard for measuring obesity and over weight .

Mora S. et al (2006) used a double blind clinical trial to establish direct association between BMI and cardiovascular risk factors in 27,138 adult women averaging 50.4 years in age. Only a similar clinical trial can contradict their findings.

While BMI and metabolic risk factors (metabolic index) have been shown to be equally sensitive in identifying obesity and over- weight when present, they are better used in combination for synergistic reasons (Buchholz A.C. et al, 2005).
Another important consideration when addressing low BMI sensitivity in obesity and overweight measurement relates to the classification of obesity.

At optimum weight a US adult has a BMI of 18.5 - 24.9 Kg/m2, an overweight adult has a BMI of 25.00 - 29.90Km/m2, while an obese adult has a BMI of 30 Kg/m2 or more. Any BMI below 18.50 Kg/m2 is classified as underweight. The overweight BMI also corresponds to the premorbid stage of obesity, when there is no sickness involved, other than the psychological embarrassment of feeling shapeless and sloppy.

Morbidity or abnormal metabolism only sets in at the obese weight level. Thus a large-sized premorbid overweight person may still weigh in as metabolically healthy. On the other hand, a marginally normal weight person may weigh in as metabolically unhealthy.

The healthy overweight person manifests what is called hypermetabolic syndrome, characterized by generalized increase in the anabolic metabolism. In people with hypermetabolic syndrome, there is increased production of normal bony tissue , muscle tissue and fat cells.

To adequately maintain the increased body mass, the anabolic hormones, including growth hormone, thyroxine and insulin are also increased within normal limits. There is also increased food demand by way of voracious appetite to meet the high metabolic demand.

How this increased appetite is managed usually determines how fast a person tilts from overweight into obesity. Poor food choices will lead to raised blood cholesterol and blood glucose, with secondary diabetes, coronary heart disease and chronic kidney disease. This is when the person becomes metabolically unhealthy.

The marginally normal weight person is usually tilted into metabolically unhealthy state by cachexic pro-inflammatory toxins (C-reactive proteins) that affect not only the heart health, but also account for the generalized weight loss.

This form of weight loss is often seen in chronic obstructive lung disease (COPD) and cancer patients. These patients also tend show normal metabolic marker results for heart health, except in cases like juvenile diabetes and familial hypercholesteremia.

Rather than castigate BMI as an obesity measurement tool, researchers should start focusing on optimum weight, which varies for individuals. By definition, the optimum weight for any individual is the weight above or below which an individual becomes metabolically unhealthy.

At optimum weight a person can be skinny or plump and still be metabolically healthy. A clearer understanding of how the weight classification of an individual can affect his/her BMI measurement, is therefore essential to the accurate evaluation of BMI reliability as a measuring tool for obesity.

References

1) Jeffrey Hunter, et al, "New loci for body fat percentage reveal link between adiposity and cardiometabolic disease risk" Nature Publishing Group,
© 2016 Macmillan Publishers Limited. All Rights Reserved.

2) S Mora, IM Lee, JE Buring, PM Ridker - Jama, 2006 - archpedi.jamanetwork.com

3) "Obesity and overweight Fact sheet N°311". WHO. January 2015. Retrieved 2 February 2016.

4) Bleich S, Cutler D, Murray C, Adams A (2008). "Why is the developed world obese?". Annu Rev Public Health (Research Support) 29:273–95.doi:10.1146/annurev.publhealth.29.020907.090954. PMID 18173389.

5) Buchholz, A. C., and J. M. Bugaresti. "A review of body mass index and waist circumference as markers of obesity and coronary heart disease risk in persons with chronic spinal cord injury." Spinal cord 43.9 (2005): 513-518.

Dr. Otumdi Omekara is a preventive/business medicine specialist and medical publisher with over two decades of clinical practice experience and over a decade of provider management experience. His passion for patient education drives his medical content article writing and publishing. He was a health educator at Oregon DHS Center for Disease Control from 2001 to 2002. Prior to that he volunteered at NE Portland Neighborhood Clinic as a health educator from 1997 to 2002. Since 2002 he has been the Medical Publisher at Drotumdio Health Publications (dHp). He lives in Portland Oregon and can be reached through his website at www.health-pub.com or by text at +1971-2085909.