What your Body Mass Index is not Telling you
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03 April 2010
By Pratibha Masand
Patients With ‘Normal’ BMI Battling Health Problems Associated With Obesity
At 17 years, Rujuta Durake was overweight but not obese. Her Body Mass Index (BMI) was 26–a figure that does not warranty the need for metabolic surgery. But not only did Rujuta undergo a gastric bypass, doctors also diagnosed her with Type 2 diabetes, a disease usually associated with obesity. Her doctors found an unusually high percentage of fat deposits around the teenager’s liver and intestine.
“Traditionally, a BMI of 30 and above is a sign of obesity. Though Rujuta’s BMI was 26, her body fat percentage was 49%, much higher than the normal limit, which is 22% for women,” said Dr Dr Shashank Shah, bariatric surgeon at L H Hiranandani Hospital. There are many people like Rujuta, who suffer from health problems associated with obesity even though their BMI does not indicate it. It’s little wonder, then, that doctors are insisting that BMI can’t be the only tool to measure obesity.
“While BMI is an accepted measurement of obesity, it doesn’t measure adiposity–a status that incorporates physiological and anatomical parameters and provides a more complete measurement of a person’s metabolism,” said Dr Muffazal Lakdawala, bariatric surgeon, Saifee Hospital.
Also, a patient’s obesity level can vary depending on composition, gender, etc. “The BMI reading of a man and woman who each weigh 75 kg will throw up the same figure. It does not take into account that while the man will have a higher fat percentage in his upper abdomen area, the women is most likely to have fat deposits around the hips. Only the male patient is likely to have problems such as diabetes and high cholesterol,” said Dr Shah, who advocates the need for a Dual Energy X–ray Absorptiometry (DEXA) scan to get an accurate measure of fat density.
Sanjay Hon, 48, was suffering from obesity–related medical problems including hypertension, diabetes and high cholesterol. This, despite the fact that his BMI was 28. His body fat, however, was a high 40%. “The doctors informed me that my abdomen had deposits of fat,” said Sanjay, who had to undergo metabolic surgery. “I managed to shed 23 kg and my cholesterol levels are normal,” he added.
But the BMI is an affordable indicator of the problem. “A DEXA scan cost up to Rs 1,500 per scan. The BMI is still a good marker to help a person understand where he or she stands. Further course of action can be taken from there,” said Dr Ramen Goel, bariatric surgeon, Bombay Hospital. Measuring Obesity
What Is BMI
Body mass index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women. It is calculated as absolute weight (kg) divided by height (m sq).
According to the 1991 National Institute of Health consensus, the cut–off criteria for an obesity surgery is a BMI 40 or 35 with comorbidity (problems like diabetes, etc). The reason BMI is used for screening the health of a patient is due to the strong correlation between being overweight/ obese and having health problems
But What About Body Fat?
According to doctors, obesity calculation should now be carried out through skin–fold thickness measurement, body fat scan, dual energy X rays, CT scan and MRI . The American Journal of Clinical Nutrition published a study showing that body–fat percentage may be a better measure of weight–related diseases than BMI. Doctors now believe that BMI limits be reduced, and other parameters like body fat percentage be considered for measuring obesity Some parameters suggested by the medical
Metabolic surgery be considered as a treatment option for obesity in Asians above a BMI of 32 Asians whose BMI is 30 and waist circumference more than 80 cm in females and more than 90 cm in males, should be considered for obesity surgery.
body fat is normal for women
For men, the limit is 17%