The Figure-Flaw Paradox: Does it really matter how your body measures up? Part 2
The “figure flaw paradox” is really a retake on the obesity paradox. As obesity has proven to be a poor measure of health or mortality risk, new renditions are being proposed. But the fallacies are the same.
We’ve encountered all sorts of spins trying to preserve the myths of the deadliness of fat — from claims that the studies only show a paradox with really old people to that being overweight might be okay but not obese — hoping we won’t actually read the studies to see that that’s not what they found. It’s unpopular to spread the news that most fat — most overweight, as well as most obese — people have lower risks for mortality than those with “healthy” weights; or that thin people, regardless of their age, fair the worst. Some discount the better outcomes among obese people by saying they get better healthcare than thinner people — something completely opposite of decades of documented discrimination against obese people in healthcare.
The suggestion we most hear trying to negate the obesity paradox is that BMI doesn’t differentiate fat (“bad”) from muscle (“good”), the assumption being that fat is bad. Increasingly trendy measurements to identify “unhealthy fat” have been proposed, including percentage body fat, waist circumference and waist-to-hip ratio (“belly fat”). Savvy readers could simply take all of the flawed studies and staticulations behind obesity and step and repeat for each new variation.
As with using weight or BMI, the same misuses of correlations in poorly controlled studies have been used to point to abdominal fat as a cause of ill health and higher mortality. Where our bodies store fat, as well as our body shapes and types, is largely genetically determined. But weight gain, especially in the mid-section, is a marker for age among the general population. Studies of populations consistently find that people who are heavier, especially in their mid-section, are older. [They’re also more apt to be yo-yo dieters and lower social class.] And age is the biggest risk for dying and diseases of old age. That’s why well-controlled and properly designed studies that remove biases such as these, are so important. A null study in epidemiology is most important to us. If a strong correlation can’t even be found, then that measurement can’t possibly be a credible cause for us to focus on.
Two independent* groups of researchers wanted to see if obesity or where fat is distributed on our bodies can predict our risks for premature death. They went to the most reliable and objective data available on Americans: actual measurements taken by specially-trained technicians on a large representative sample of the population and actual mortality data. The Third National Health and Nutrition Examination Survey (NHANES III, 1988–1994) conducted the most precise measurements of body size, measurements and composition available on a large representative sample of the U.S. population (including BMI; body fat percentage measured by bioelectrical impedance; skinfold thickness; circumferences of waist, hip and arm; waist-hip ratio; and waist-height ratio). National death certificate data in the national Death Index linked mortality data through 2000 to these detailed measurements in NHANES III.
We recently reviewed the findings from senior scientists at the National Center for Health Statistics at the Centers for Disease Control and Prevention (CDC) and the National Cancer Institute. In a nutshell, the data showed that no higher measurement of body shape or size, or body composition, is predictive of higher risks of dying from all causes, compared to people with “healthy” numbers and model figures. Nor was there a net benefit of using BMI versus another measurement. The data also found that NONE of the 21 diseases popularly attributed to obesity — those “obesity-related” diseases, including: cardiovascular disease, cancers (colon cancer, breast cancer, esophageal cancer, uterine cancer, ovarian cancer, kidney cancer, or pancreatic cancer) and diabetes or kidney disease — are actually associated with excess deaths at any BMI category, including obese.
Another group of researchers, led by professor Jared P. Reis, Ph.D., with Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, used the same nationally representative data on adults aged 30 years and older, and applied different statistical modeling to investigate the associations between BM, body fat, and various body measurements to mortality. They approached it from a different perspective regarding hypotheses about causal relationships to obesity-related conditions, noting: “We did not adjust for physical activity or possible mediators of obesity effects, such as diabetes, hypertension, or high cholesterol, since doing so would have resulted in over adjustment because of their position on the causal pathway.”
Did they show the same null findings as the CDC scientists? It turns out “yes,” but you have to look closely to realize that.
Their data showed
Their findings, published in Obesity, the journal of the Obesity Society, weren’t widely published in mainstream media. And those who glanced only at the abstract missed the results demonstrated in the data itself.
First, not surprisingly, most predictive of mortality was age. The men and women who died during the 12 years of follow-up were significantly older (20.7 years older among the men and 21.3 years among women). Among the younger men (30-64 years), only 7.5% died over 12 years of follow-up compared to 48.5% of older men (65+ years); and only 4.9% of the younger women (30-64 years) died during those 12 years, compared to 36.76% of the older women.
In examining the risks associated with BMI and the various body measurements and ratios, they adjusted for baseline age, race/ethnicity, education, smoking status, alcohol use, heart disease, stroke, respiratory disease and cancer (except nonmelanoma skin cancer). Their findings revealed:
● Among younger men, there was no statistically significant correlation between BMI, waist circumference or waist-hip ratio and risks for death from all causes.
● Among older men, mortality risks were inversely associated with each measurement — risks of death were lower the higher the BMI and waist circumference — with the fattest men associated with a 30-40% lower mortality risk compared to those in the ‘normal’ range. Even the men with the highest waist-hip ratios were associated with nearly half the risk of death of lean men.
● Among the younger women, there was no statistical difference in BMIs or waist circumference and risks for dying. So few young women died in each quintile over the 12 years (0.4% a year in the national sample, 18 women), that looking at hazard ratios alone exaggerates perceptions of actual risks, anyway.
● Among the older women, BMI was inversely associated with mortality. The highest risk for death was among lean women with low BMIs. Fat women of all sizes were associated with lower risks. The most “obese” women with the highest BMIs had a 23% lower risk for mortality compared to “normal” weight women. There was no correlation between waist circumference or waist-hip ratios and the women’s risk for death, although all of the larger sizes had lower risks than thin women.
To limit potential confounding influence from existing or subclinical diseases, the authors also adjusted for “clinically manifest disease at baseline and excluded deaths within the first 5 years of follow-up” and the results were the same.
Do you see the grossly higher risks for death among obese people, according to their BMI, waist-hip ratio or waist-thigh ratio? If you can’t, it’s because they aren’t there, of course. The risks of adiposity have been exceedingly oversold to the public.
Abdominal fat, or central adiposity, has been a topic of frequent interest and some have suggested it be used rather than BMI to evaluate mortality, under the belief that unhealthy visceral fat is the underlying reason for morbidity and mortality associated with overall obesity, wrote Dr. Reis and colleagues. In their review of the literature, they noted that waist circumference has been more highly correlated with visceral fat than waist-hip ratio or waist-thigh ratio. However, studies to date have not consistently supported a correlation between abdominal fat or body fat distribution as predictive of mortality. Nor has waist circumference been consistently shown to be more strongly associated with type 2 diabetes, cardiovascular disease or mortality than waist-hip ratio, they said. “Therefore, it is clear that waist-hip ratio and waist-thigh ratio do not reflect variation in visceral fat accumulation,” they wrote. [We’ll look soon at the definitive clinical trial that disproved the visceral fat hypothesis.]
The only barely statistical correlation they found was waist-thigh ratio in young men and elderly women. While this may be of interest to those still selling those thigh masters made popular by Suzanne Somers, the notion of spot reducing our way to better health or longevity was debunked long ago. A biologically plausible explanation for continuing down the body to look at other measurements is so far removed from science — we’re sooo not going to go there. Of course, that hasn’t stopped people from marketing weight loss programs to treat “fat ankles” and surgeons even treating “toebesity” with surgery to slenderize generously-proportioned digits.
The belief in the unhealthiness of body fat is so ingrained that it can sadly lead anyone to be unable to grasp the reality of the evidence. Dr. Reis wrote that the findings in their study suggests “that it is not only important to have a low BMI but also a low amount of abdominal adiposity to lower your risk of death.” Dr. Reis and colleagues wrote in their concluding paragraph:
In conclusion, we provided evidence on the relative importance of well-defined measures of overall obesity and abdominal adiposity or body fat distribution in assessing risk of total and cardiovascular disease mortality in a nationally representative sample of US adults. Despite their limitations, ratio measures of body fat distribution were strongly and positively associated with risk of mortality in middle-aged adults. In addition, WHR and WTR increased prediction of mortality among normal weight and obese middle-aged adults. Among the elderly, a higher BMI in both sexes and WC in men were associated with a lower risk of mortality, while indicators of body fat distribution increased survival or did not influence risk of mortality. These results suggest that ratio measures of body fat distribution carry important information for identifying middle-aged adults at increased risk of mortality and therefore should not be abandoned in research or practice.
Are those the conclusions you would have reached after an objective examination of the findings? The importance of independently thinking and looking at what a study found, rather than taking abstracts and authors’ interpretations of the findings as the same thing, are especially evident when it comes to the obesity paradox.
© 2009 Sandy Szwarc
* In a private email from Dr. Reis, he indicated that they hadn't known that Dr. Katherine Flegal, Ph.D., and colleagues at the CDC had also examined body shapes, measurements and composition. “The major difference between our study and those of Katherine Flegal is that we added information regarding central obesity or body shape including waist circumference, waist-to-hip ratio and waist-to-thigh ratio,” he wrote.