The Fit-Fat Fight Reignites

The fit-fat fight -- whether someone can be obese but still healthy -- has reignited (if it ever really stopped) with an article in the Archives of Internal Medicine that was reported in the NYTimes.

Wildman et al. used data from the NHANES study and looked at the relationship between Body Mass Index (BMI) and whether the individuals had a variety of other indicators of cardiovascular risk -- mostly blood tests that indicate poor cardiometabolic physiology like high cholesterol or high blood pressure. What they found was that large numbers of obese individuals (BMI > 30) had few indicators of cardiovascular risk and large numbers of normal weight individuals (BMI

Basically, the conclusion forwarded in the Times coverage is that it may not matter whether you are obese, just so long as you are physically active.

The reality, I think, is a bit more complicated.

For starters, I agree that BMI is not a great indicator of cardiovascular risk. Because BMI incorporates only information about body mass and height, it ignores groups that may be low risk even though they have large BMIs. For example, the very physically active may be classified as obese even though they have little adipose tissue and very healthy hearts. Likewise, there are a lot of skinny unhealthy people out there -- groups like thin smokers or the frail elderly -- whose high risk is not captured by that number. Body fat distribution also matters. People who carry their fat in their stomachs are at higher risk than those who carry it in their thighs.

However, just because quantifying the relationship between adiposity and cardiovascular risk is difficult doesn't mean that adiposity is unrelated to cardiovascular risk. I wrote in my earlier post that this is why a lot of doctors are moving to measures like waist circumference and waist-to-hip ratio as more predictive measures of cardiovascular risk. If those measures work better, so be it. It is still something your doctor should be concerned about.

Further, high cardiovascular risk is not the only negative association with obesity. There are a lot of other things that can go wrong when you are obese, some of them regardless of whether you are physically active or not. These include diabetes, osteoarthritis, and sleep apnea. (Reviewed here and here.)

Of these, the greatest concern is type II diabetes because it is also a risk-factor for cardiovascular disease. Further, though high physical activity is associated with lower diabetes risk, your risk is still related to adiposity regardless of how active you are. In women, overall adiposity appears to have a greater effect on risk than physical activity. Basically, we refer to obesity and exercise as independent risk factors for diabetes. You can indeed lower your risk by exercising, but you could lower it still more if you lost weight. Because obesity and low physical activity are related, we still recommend weight control as a first step in fighting diabetes risk. Thus, the data with respect to diabetes suggest that being an active obese person is still not entirely healthy. An active person may be fine from the standpoint of cardiovascular health, but diabetes (and other things) are still an issue.

My point is not to diminish the positive benefits of exercise nor to suggest that BMI or weight or anything else is a perfect measure of risk. It may even be that exercise is more important than losing weight. My point is that you should not conclude from articles like this that weight control is not a legitimate medical goal. Doctors should be encouraging their patients to exercise, but they should also be encouraging their patients to lose weight.

Fortunately -- despite an unclear association between the two -- increased activity is still the recommended means of weight loss. Thus, the effect may be the same. Before your doctor told you to lose weight by exercising; now he may just tell you to exercise as a legitimate goal in itself.

Hat-tip: Chad

More like this

BMI or Body Mass Index is a measure of obesity that is used to approximate the health problems associated with being overweight. It is really easy to calculate. The formula for it is weight in kilograms divided by height in meters squared. Here are some calculators for those of your reluctant to…
If you go to your physician's office and inquire about your weight status, he or she will measure your height and weight to derive your BMI (weight in kg divided by height in m squared). Then they will compare your BMI to that of established criteria to decide whether you are underweight (<18.5…
Peter Janiszewski at Obesity Panacea has posted a fascinating series on the issue of people who are obese but metabolically healthy. We worry about rising rates of obesity because obesity increases the risk for health problems like diabetes and cardiovascular disease -- but what if that's not…
Recently, it seems there has been a backlash against medicine and the current knowledge of the relationship between diet, weight and overall health. I don't actually believe this is directly the fault of scientists or doctors, who react to the trashy mainstream reporting of science with little…

BMI != measure of fat. Body fat can be measured in a variety of ways, BMI is not one of them. BMI strictly measures body mass by height.

BMI is a good proxy for body fat simply because the vast majority individuals with high BMIs can attribute their weight to excess body fat, not muscularity. Eyeballs can easily differentiate fit from fat if that is necessary. Something that should be noted is that those with high BMIs due to heavy athletic training or work can rapidly go from muscular to fat when the exercise is stopped while dietary habits continue.

The idea of "fit and fat" has been known for at least 15 years from the data compiled by Steven Blair, epidemiologist at the Dallas Cooper Clinic.

By natural cynic (not verified) on 20 Aug 2008 #permalink

Natural cynic wrote:

"Something that should be noted is that those with high BMIs due to heavy athletic training or work can rapidly go from muscular to fat when the exercise is stopped while dietary habits continue."

Cycling champion Greg Lemond has recently filled out a bit as well... Any retired athlete or manual laborer that does not adjust their calorie intake for a more sedentary life is going to get fat. Exactly why are we supposed to "note" this pointless and unsubstantiated prediction about what currently muscular people will eat or weigh in the future? The issue at hand is the correlation between cardio vascular health of individuals as a function of their current BMI, not our expectations about what they might weigh in the future.

By cycling fan (not verified) on 20 Aug 2008 #permalink

Re cycling fan

Relative to Greg Lemond showing signs of becoming somewhat portly, I would refer Mr. cycling fan to a photograph of 5 time winners of the Tour de France taken with Lance Armstrong. One of those in the photograph was Eddy Merkx who has become more then portly. He has become downright fat.

"Doctors should be encouraging their patients to exercise, but they should also be encouraging their patients to lose weight."

Why should they be encouraging their patients to lose weight, given that the medical profession doesn't know how to produce significant long-term weight loss in the vast majority of patients? Why not concentrate on health improvements that can be achieved (e.g. exercise)?

Why should they be encouraging their patients to lose weight, given that the medical profession doesn't know how to produce significant long-term weight loss in the vast majority of patients? Why not concentrate on health improvements that can be achieved (e.g. exercise)?

It's really simple: calories in < calories out. Compliance is the problem. The best thing to do to insure success is to exercise a lot. Again, compliance is the key. How to get a significant percentage of patients to comply is the unknown.

Exactly why are we supposed to "note" this pointless and unsubstantiated prediction about what currently muscular people will eat or weigh in the future?

The interesting thing to note is that when calories out volitionally decreases, calories in naturally does not follow to the same degree - an interesting problem about habits and hormones. Also, even if the weight remains stable [rare], the % body fat increases - one of those cases where BMI is not a good measure of fitness or % fatness.

By natural cynic (not verified) on 21 Aug 2008 #permalink

SLC wrote:

"Relative to Greg Lemond showing signs of becoming somewhat portly, I would refer Mr. cycling fan to a photograph of 5 time winners of the Tour de France taken with Lance Armstrong. One of those in the photograph was Eddy Merkx who has become more then portly. He has become downright fat."

It is impossible to ignore the fact that Eddy Meckx is indeed fat; is there a larger conclusion you intend to draw from this?

By cycling fan (not verified) on 21 Aug 2008 #permalink