Redefining obesity? The experts weigh in on BMI s validity

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In the United States, 66 percent of adults are categorized as either overweight or obese a number is three times what it was in 1980. Elevated body mass index, an estimate of body fatness based on height and weight, has long been considered a risk factor for coronary heart disease, stroke, and cancers of the large intestine, kidney, uterus, and breast in postmenopausal women. Furthermore, 20 percent of adults aged 20 years or older have metabolic syndrome, defined by a combination of obesity, hypertension, dyslipidemia, and insulin resistance. In those 50 years and older, that number is 30 percent. Additionally, cardiovascular disease has been the leading cause of death in the westerns world and one of the major contributing factors is obesity.

We have now seen another side of the story, however. In early January a meta-analysis from the Centers for Disease Control and Prevention was published in JAMA. Dr. Katherine Flegal and colleagues analyzed data from over 100 studies and 3 million people to clarify the relation between overweight, obesity and risk of death. Based on Body Mass Index, they concluded, in part, that the risk of mortality was lower for people who were overweight than for those whose BMI fell in the normal category; in addition, the data indicated that older people (65+) whose BMI put them in the group labeled severely obese did not have an elevated mortality risk.

What can we make of these data that seem to contradict what we think about obesity? To try to sort things out, we asked experts in the field to send us their thoughts about the study and its conclusions. Here are their responses:

Nancy Cotugna, Ph.D., R.D., C.D.N., University of Delaware

The respected obesity researchers who did the study certainly raise some questions about the obesity/mortality connection. But is death all we are thinking about - what about all the other consequences of overweight and obesity such as diabetes, hypertension, arthritis and cancer? And is BMI the best measure to determine weight/fat status albeit the one that most used. Some of the newest research even states that we should lower the BMI definition of overweight! I'm not changing my current thoughts on the obesity problem.

Barbara J. Moore, Ph.D., President and CEO, ShapeUp America!

I believe this recent meta-analysis is consistent with earlier studies showing the same thing overweight is not associated with increased mortality. When the original NIH guidelines on the treatment of adult obesity came out in draft form, many of us objected to the argument that the definition of overweight should be changed from a BMI of 27 to BMI of 25 on the grounds that mortality is increased among overweight individuals. I felt the published studies at that time did not support that argument. I discussed the problem at considerable length with Katherine Flegal (at the CDC) at that time and have stayed in touch with her over the years. I believe she is an excellent scientist and that her conclusions about mortality are likely to be correct.

There is no doubt, however, that overweight is associated with increased morbidity and that consumers are likely to be confused about this.

Anonymous scientist

(An employee of the federal government who asked for anonymity because of rules prohibiting federal workers from criticizing federal policies).

I am not surprised at the report in JAMA. This is certainly not the first report that has found reduced risk of death in people who are overweight by the current definition using BMI, but it summarizes previous published studies and thus has, by far, the largest number of subjects analyzed. Until 1998, the U.S. considered normal weight up to a BMI of 27.8. That was primarily because the lowest claims on life insurance were associated with that weight range. In 1998, NIH and CDC got together and aligned the U.S. cutoffs for overweight and obesity with those of the World Health Organization. These decisions have as much political maneuvering as science behind them.

BMI correlates with fatness but was not designed to be used for individuals, only for population averages. So, people like Michael Jordan or Barry Sanders were considered obese because of their high BMIs when they were playing professional sports.

But mortality is not the only important issue associated with overweight/obesity. Diabetes prevalence has tripled, the incidence of fatty liver has increased and medical costs for these conditions are enormous. Likewise, the number of joint replacements because of obesity has skyrocketed and the dollars paid for these all come partially from government programs. So quality of life may be compromised and medical costs elevated without any effect on mortality, which was the only focus of the recent JAMA paper.

Stanley S. Young, Ph.D., National Institute for Statistical Sciences

Most people would like to know the causes of early death so that they might plan to mitigate factors under their control. Two uncontrollable factors are gender and genetics, and they likely are the most important factors. Smoking, exercise, alcohol consumption, and body weight are nominally under an individual's control. Of course, body weight consists of muscle, bone and fat, and it is fat that comes under attack. H. L. Mencken commented, The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. Mencken would understand the war on obesity quite well. The recent JAMA paper on BMI and obesity aims to bring some reason from data and analysis to the discussion. What is at issue? A simple position is that the fatter you are the more likely to die, which makes for a simple war-on-obesity message. Flegal et al. make the case that people with modest obesity actually live longer than people of defined normal weight. Consternation. Simple scare-mongering may be misleading at best or actually wrong. We currently approximate how fat a person is by body-mass index. Mencken provides insight here as well, For every complex problem, there is a simple answer. And it is wrong. BMI is defined as weight in pounds, divided by height in inches squared, then multiplied by 703 to adjust for the use of British units. Being 5' 7 and 160 lb. I have a BMI of 25.06 just surpassing the high end of normal, 25.0. Am I to worry? BMI is a very rough approximation for how fat a person is. Bialik, WSJ, 12Jan2013 points to a study showing that men with a BMI of 25 had a range of body fat from 13.8 to 35.3%. Women with a BMI of 25 had a range of body fat from 26.4 to 42.8%! BMI is a very poor approximation to how fat an individual is. BMI averaged over many individuals might give a good approximation for how fat the group is, but it is a very poor estimate for an individual. Two individuals, a trained athlete and a couch potato, each with a BMI of 25 would be very different creatures!

So, where does it leave us with the claim made in the JAMA paper. Is it actually beneficial to be modestly obese? They make a good case that for public health, BMI up to the level of 30 is arguably OK. There is no simple answer for the individual as BMI is a very imperfect measure of obesity. Don't smoke, drink in moderation, exercise and don't pay any attention to the grant-seeking scare-mongers. Flegal et al. are to be thanked for a balanced look at the obesity situation.

Geoffrey Kabat, Ph.D., Epidemiologist, Albert Einstein School of Medicine

Dr. Kabat recently presented a discussion of Body Mass Index and its utility in Forbes in which he presented the following points:

1. BMI is an estimate, not a measurement of fatness

2. BMI does not differentiate between lean and fat tissue

3. BMI is useful for examining the status of a population, but not of individuals

4. The CDC's recent article is only about risk of death, but as noted by others, it does not examine the effects of BMI on risk of illnesses such as diabetes, high blood pressure, and arthritis.