Saturday, January 19, 2013

Weight and class: who is obese and why should we care?

One of the things that people are most fixated upon, in both the health arena and in society at large is weight. In popular culture, weight is a major issue. Celebrities are (mostly) thin; when they are not, and look like more of the regular people who are around us, they are seen as unusual. Diet books and “fad” diets abound as do classes to help us exercise. Issues of body image are major stressors for adolescents in particular, and health problems like anorexia are all too common. And, yet, an increasing number of Americans are obese, and health problems that are certainly associated with obesity – notably, but not only, Type II diabetes – are rapidly growing.

There is a major class association with weight; as income and class go down, prevalence of obesity goes up. Perhaps ironic compared to earlier centuries, when being heavy was associated with money – that is, the ability of the person to afford all that food – and poor people were starving. But if ironic, it is serious; the abundance of cheap, high-calorie foods in our society mean that poor people are not denied the opportunity to have lots of calories, but the stressors of poverty that affect all aspects of social life are still there, creating obesity as just one more problem to be confronted (or not).

In this context, a recent article in JAMA by Katherine M. Flegal and colleagues has garnered a lot of attention. “Association of All-cause mortality with overweight and obesity using standard Body Mass Index Categories: A systematic review and meta-analysis[1], reviewed 97 studies with over 2.8 million people and encompassing 270,000 deaths, and performed a meta-analysis (a set of statistical techniques that allows accounting for studies that are somewhat different in design and have different numbers of people). The results were that people whose body mass index (BMI, a ratio of weight to height) was in the “overweight” range (25-30) had lower all-cause mortality than those in the “normal” range (18.5-25). In fact, the all-cause mortality rate was no higher for those in the range of “grade 1 obesity” (30-35) than for those in “normal” weight range. However, it was higher for those with grade 2 obesity (35-40), grade 3 obesity (>40) and for all obesity taken together (>30). In addition, unsurprisingly, the “hazard ratios” for mortality were greater for the same BMI when heights and weights were self-reported rather than measured (suggesting people under-estimate or under-report their weight, which would mean their BMIs are actually higher than reported).

This is not, of course, really new news, since all of the studies reviewed had been previously published. There was already a sense among many in the medical field that people at the “low end” of overweight (say 26-27) might be as least as healthy (have as low a mortality risk) as those at the low end of “normal” (18.5-25).  Heymsfield and Cefalu, in their editorial commenting on this study, “Does body mass index adequately convey a patient’s mortality risk?”,[2] say “Persons with a BMI between 18.5 and 22 have higher mortality than those with a BMI between 22 and 25. Placing these persons in a single group raises the mortality rate for the normal weight group. The average resulting from combining persons in the lowest mortality category (BMI of 22-25) with those who have greater mortality (BMI of 18.5-22) might explain why the NHLBI category of normal weight has an observed mortality similar to class 1 obesity (BMI of 25-30).”

If people with a BMI of 18.5-22 have a higher mortality rate than those with a BMI of 25-30, why, for goodness sakes, is 18.5-25 considered “normal”. For reference, a 5’4” person with a BMI of 18.5 would weigh about 108lbs, at a BMI of 22 it would be 128lbs, at 25, 145lbs, and at 30, 175lbs. For a person who is 5’10”, the weights at the same BMIs would be about 129, 152, 174, and 207. I think most people would not think that the lower range was normal except for models and marathon runners (hey, I’m overweight and would like to lose about 10-15 pounds of fat, but I think I’d be pretty sick before I lost the 60 lbs needed to get me to 22! My son was heavy when he developed Type I diabetes as a young adult, and went from a BMI of about 32.5 to about 21; let me tell you, he looked bad!), but the real question is “what are the healthiest ranges to be at”? This is what official recommendations should be based on, and it is clear from the work reported by Flegal and colleagues that this is not the case for the current numbers.

The relationship between adiposity (presence of significant amounts of excess fat) and risk for many diseases is well-established; the relationship between adiposity and BMI less well so. Variables include amount of muscle mass (not a risk factor but leading to greater weight-for-height), sickness (people who lose weight as a result of disease), and overall body structure. I tried to find out where these ranges come from, but have, so far, been unsuccessful. I found the references to the “Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults”, put out by an expert panel in 1998, but at least their “Executive Summary”[3] does not reveal the source of how the “normals” were derived; they are just asserted. 

Obviously, this is going to be controversial. Paul Campos’ op-ed piece in the NY Times on January 3, 2013, Our absurd fear of fat”, makes many of the same points I have, but letters generated in response range from those lauding it and saying people (especially children) should be taught to be proud of their bodies, to those arguing it minimizes the health dangers of obesity. What is clear, though, is that the fixation on “ever thinner” that exists in much popular culture has no place in health discussions. The JAMA article strongly suggests that our standards for “normal”, “overweight” and “obese” BMI are too low, although not irrelevant. It calls our attention to a tendency to other similar areas in which health professionals have adopted uni-dimensional disease markers and driven them even lower, to result in poor health outcomes for many. Recent examples include blood sugar (or its related value, hemoglobin A1c), blood pressure, and cholesterol. Studies that held everything else equal found benefit in lower values, so experts kept driving down the definitions of normal and desirable for these tests. Unfortunately, not everything else is equal. Pushing the desirable hemoglobin A1c level of people with diabetes to 5% instead of 6% led to a lot of morbidity from hypoglycemia; lowering cholesterol goals led to toxicities from drugs; lowering blood pressure goals to poorer functioning and greater mortality in some populations, especially the elderly. Most people don’t exercise regularly, but rather than lauding all efforts to exercise, “experts” keep raising the bar for how often, how long, and how intense exercise should be.

So let’s get back to class, and its associated characteristics. It is time for health professionals to recognize that they are also social service professionals and members of a society whose broad policies have a much more profound impact upon health than small numbers variation in BMI, blood pressure, cholesterol, and blood sugar. We need to treat, as well as support and encourage, people at the extremes whose health is at risk, but we shouldn’t fall prey to definitions that name more people as diseased and needing interventions and distract us from the real business at hand.

Which is creating a more just, fair, equitable and safe society.

[1] Flegal KM, et al., “Association of All-cause mortality with overweight and obesity using standard BMI Categories: A systematic review and meta-analysis, JAMA Jan 2 2013;309(1):71-82
[2] Heymsfield SB, Cefalu WT, Does body mass index adequately convey a patient’s mortality risk?” JAMA Jan2 2013;309(1):87-88.
[3] Expert panel, “Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults: executive summary”, Am J Clin Nutr, 1998;68:899-917.


Josh Freeman said...

My attention has been called to this blog by Dr. Alan Niedermann,, and its reference to the work of Adolphe Quetelet. It still doesn't explain how the current "normal" values were derived, though.

Verla said...

This is cool!

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