Sunday, August 25, 2013

Fit or Fat? BMI Won't Tell You

Weight has always been a struggle for me. I have never doubted the proposition that it's better to be fit than to be fat because obesity greatly increases your risk of chronic, life-shortening diseases. However, I will confess that the common yardstick of the body mass index (BMI) has always irritated me. A simple formula taking into account your height and weight yields a number that is supposed to tell you with certainty if you are underweight, normal, overweight, or obese.

I don't doubt that despite trimming 25 pounds gradually since I hit my 60s, I still have more weight that I need to lose. I weigh myself, I exercise, and I try to be careful about what I eat. Nevertheless, I do think that large-framed folks (or "big-boned," whatever you want to call us) have not gotten a fair shake from the BMI. When I was a schoolboy, I was the heaviest guy on my football team, but I ran the wind sprints in the August two-a-days with all the others. In middle age, I was still a big guy but I ran a variety of road races, and always completed them, even a few 26.2 milers. Nowadays, I understand some schools even send kids home with their BMIs, as though it is a report card that could shame them as being obese.

Now, I have some impressive scientists on my side. The following is the lead paragraph from the August 22 edition of Science Daily:

"Researchers from the Perelman School of Medicine point out that the body mass index (BMI), based on the weight and height, is not an accurate measure of body fat content and does not account for critical factors that contribute to health or mortality, such as fat distribution, proportion of muscle to fat, and the sex and racial differences in body composition."

Note they don't even say (as some height/weight charts do) that BMI has limitations. They said it "is not an accurate measure." That sounds unequivocal to me, so I hope skinny-minnies will quit flaunting their  BMI numbers in my presence.

The need for an accurate measure has grown because of an outbreak of controversy over the health effect of obesity. As the Perelman people note, obesity "predisposes to diabetes, heart diseases, sleep apnea, cancer, and other diseases." Yet, some recent research studies of old folks have indicated obesity has some sort of protective effect from assorted causes of death including the chronic ones of stroke, heart failure, and diabetes. Needless to say, that research has provoked a great deal of controversy. Maybe we can delve more deeply into that in a future post.

The point today is science needs a far better measure than BMI to tell us how much fat we're carrying around and how it may be really bad for us. As Dr. Rexford Ahima, one of the lead researchers, wrote in the journal Science:

"There is an urgent need for accurate, practical, and affordable tools to measure fat and skeletal muscle, and biomarkers that can better predict the risks of diseases and mortality. Advances to improve the measurement of obesity and related factors will help determine the optimal weight for an individual, taking into account factors such as age, sex, genetics, fitness, pre-existing diseases, as well {as} novel blood markets and metabolic parameters altered by obesity."

Optimal for an individual. Sounds good to me, since we are individuals, you know.  I'll drink a V-8 juice cocktail to that.

                                               © Robert G. Holland

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