by Kenneth W. Krause.
Kenneth W. Krause is a contributing editor and “Science Watch” columnist for the Skeptical Inquirer. Formerly a contributing editor and books columnist for the Humanist, Kenneth contributes regularly to Skeptic as well. He may be contacted at firstname.lastname@example.org.
In thoughtful response to my recent SI column, “Obesity: What Does the Science Really Say (Or Not Say)?” a number of readers wrote to me or the editor raising crucial issues deserving of an equally considerate response. As such, and because a great deal of new science has been published on the subject, I’ve chosen to forego the Letters section and address these readers’ concerns here.
One foundational question tends to resurface every few years or so. It asks whether excess adiposity is in fact a serious health problem, as prevailing medical opinion has dictated for more than a half century, or whether it is just as well or even better to be fat.
A new JAMA study on the topic caused quite a stir this year among both the popular media and public health officials (Flegal, et. al., 2013). Four American and Canadian researchers led by Katherine Flegal of the National Center for Health Statistics, Centers for Disease Control and Prevention in Hyattsville, Maryland reviewed 97 studies providing a sample size of more than 2.88 million individuals and 270, 000 deaths to calculate all-cause mortality hazard ratios for standard body mass index (BMI) classifications(1).
Flegal’s results caused some lay observers to inquire, as Slate Magazine’s William Saletan did on January 2, “Is Fat Good?” Her team reported as follows: Relative to normal weight, all combined grades of obesity were associated with an 18 percent higher incidence of all-cause mortality. In cases of more extreme of obesity, the association rose to 29 percent. By itself, however, the mildest grade of obesity was not correlated with a significantly elevated risk, and the overweight but not obese category was actually associated with a 6 percent lower incidence of all-cause mortality.
Interesting data, to say the least. But how should they be responsibly interpreted? Unsurprisingly, much of the popular media, along with certain food and drink special-interests, focused on one possible explanation they assumed their audiences and customers would prefer to hear—essentially that overweight as a general proposition can be a positive thing.
On the other hand, certain popular sources failed to report Flegal’s own list of potential explanations, including an “earlier presentation of heavier patients” and a “greater likelihood of receiving optimal medical treatment.” In such instances, those inclined for whatever reason to favor a positive appraisal of excess adiposity should be prepared and willing as well to endorse an increased need for frequent medical attention.
But the so-called “obesity paradox” is nothing new. Since the 1980s, it has typically proposed that, although overweight raises a person’s risk of diabetes, heart disease, cancer, and many other chronic illnesses, some people—particularly the ill and those of middle-age or older—might actually benefit from a little, though never a lot of extra weight (Hughes 2013).
Indeed, in an editorial to Flegal’s study, two physicians suggested that slightly elevated BMIs in patients suffering from certain chronic diseases, acute catabolic illnesses, and even traumatic injuries might be sensibly associated with lower mortality (Heymsfield and Cefalu 2013). If so, it becomes apparent why overweight or even mild obesity could both increase the risk of life-threatening diseases and decrease mortality rates.
But no responsible health care professional endorses excess weight gain generally. In fact, at least one recent study has linked higher BMIs to not only the aforementioned physical ailments, but to impaired cognition and poorer memory in post-menopausal women as well (Kerwin et. al. 2010). In addition, other experts continue to warn, for example, that “individuals exposed to maternal obesity during fetal life are at increased risk of becoming overweight or obese children and adults themselves, thus perpetuating the vicious cycle of obesity” (Gillman and Poston 2012).
We should of course remain open to all potential subtleties regarding adiposity and health. But given the depth and breadth of the evidence associating extreme overweight with all manner of affliction, the primary public-health objective must be to prevent both obesity and pre-obesity(2).
Other readers have questioned or commented on the efficacy of certain popular diets. It should be acknowledged from the start, of course, that good health is primary and that only diet plans holding nutrition above or alongside weight-loss or weight-maintenance are worth consideration. In fact, both my research and personal experience lead me to believe that the only truly effective weight-loss diets are also exceptionally healthy ones.
Experts have now established that the typical Western diet—one replete with fried and sweet foods, processed and red meats, refined grains, and high-fat dairy products—is less than ideal, to put it most diplomatically. A recent British study, for instance, followed 3775 men and 1575 women of middle-age for an average of sixteen years and concluded quite sweepingly that adherence to Western-style cuisine significantly reduces the prospect of “ideal aging,” i.e., remaining free of chronic diseases and retaining high physical, mental, and cognitive functionality (Akbaraly et. al. 2013).
That much resolved, the implied query remains: With what should we replace the typical Western diet? I recommend that we begin by conceiving of a “normal” diet. In other words, why not define appropriate nutritional habits (yes, plural) scientifically as ones offering foods and portions that the human species, or perhaps slightly more specific human populations, evolved to consume? From there, individuals can and must fashion more exclusive diet plans that suit their particular objectives and biological circumstances.
As one reader observed, some inclined toward an evolutionary definition have endorsed the “Paleo” diet, based on the assumed consumption habits of our ancestors who lived from 2.5 million to 10,000 years ago. Thus, all foods invented during or after the agricultural revolution are unceremoniously expunged from the menu. On the obviously positive side, Paleo dieters exclude all processed sugars, meats, and grains. More controversially, however, they eliminate dairy, peanuts, lentils, beans, and peas, for example.
Like many her colleagues, biologist Marlene Zuk has judged the Paleo diet’s logic a fundamentally flawed fantasy (Zuk 2013). First, says Zuk, we shouldn’t even hope to construct a nutritional plan based on the distant past when so much has changed in recent millennia, including the biology of every species of plant, animal, and human on the planet.
Second, Paleo diet dogma denies its followers the benefits of some exceptionally nutritious fare. Dairy is rich in calcium, for example, whole grains are packed with fiber and vitamins, and legumes are replete with protein. Consider the various circumstances of consumption as well. Why, for instance, should athletes rebuff easily digested sources of carbohydrates that help them recover quickly and safely from especially vigorous exercise?
Finally, the Paleo fixation ignores the heterogeneous nature of our ancestors’ environments and assumes an ideal past that never existed. The truth is we don’t know exactly how much meat, fish, fruit, or even primitive grains our Pleistocene forbears ate, or at what precise stages of their evolution. What we do know is that, to survive, they had to be flexible—not doctrinal.
Another reader contemplates the Mediterranean diet, also the subject of recent popular headlines. One especially noteworthy study, published last February in the New England Journal of Medicine, contrasted the cardiovascular health benefits of one low-fat diet with those of two Mediterranean-style diets—one supplemented with nuts, the other with extra-virgin olive oil (Estruch et. al. 2013). After following 7447 randomly assigned Spaniards at risk for heart disease, the investigators found that, relative to a low-fat plan, adherence to either Mediterranean plan reduced a patient’s risk of suffering cardiovascular death, myocardial infarction, or stroke by thirty percent.
So exactly what did the Mediterranean dieters eat? In addition to either nuts or olive oil, participants consumed at least three daily servings of fruit, and at least two servings of vegetables. Fish was eaten at least three times per week, as were legumes. The menu offered white, but not red meats and permitted the drinking of wine. On the other hand, subjects avoided cookies, cakes, and pastries completely, and limited their consumption of dairy and processed meats.
Perhaps most notably and controversially, however, the authors’ data tend to refute the long-standing conviction that fat intake must be reduced to promote cardiovascular health. So what of vegetarianism, one might reasonably wonder—is its well-documented reputation for good health at least somewhat overblown?
Not according to a group of researchers from Loma Linda University who recently studied 73,308 male and female Seventh-day Adventists (Orlich et. al. 2013). Participants were categorized as nonvegetarians, semi-vegetarians, pesco-vegetarians (accepting seafood), lacto-ovo-vegetarians (accepting dairy and eggs) or vegans (excluding all animal products). After an average of six years per subject, 2570 deaths were recorded.
Overall, the group calculated a twelve percent lower adjusted hazard ratio for all-cause mortality in the combined vegetarian versus nonvegetarian categories. Oddly, the association was far stronger for men (vegan males scored a twenty-eight percent lower hazard ratio than nonvegetarians) and less than statistically significant for women.
When considered in light of the “hormonal/regulatory defect” hypothesis proffered by writers like Gary Taubes and Robert Lustig, recent studies and commentaries offer considerable, though certainly qualified and incomplete, guidance for the obese and severely overweight.
First, though solutions may appear simple, their execution will doubtless prove otherwise. For those leading an “average” or “typical” lifestyle, thoughtful and significant changes are unavoidable. Second, ample portions of vegetables and fruits are the mainstays of any successful diet. Lean unprocessed meats, healthy oils, dairy, and whole grains—though clearly valuable—should probably be conceived of as nutritional supplements, not as staples. Empty calories, including all sweets and processed grains, should be erased from the menu until personal experimentation reveals them tolerable to whatever extent. Finally, each individual must fashion his or her own solution. Even the most successful popular diets should be scrutinized for their respective strengths and weaknesses, and then summarily rejected.
Tragically, the politics of frustration and anger have intruded deeply into the obesity discussion, as yet one more reader has suggested. Concerned citizens are frequently implored or even coerced to deny the only interventions that have ever succeeded: those which emphasize education, individual experimentation, and personal responsibility. In their absence, we are encouraged instead to blame a faceless and unoffendable community for the obese person’s choices at the supermarket, restaurant, and home.
Taubes, Lustig, and others claim that personal responsibility is irrelevant. They allege that the biological obstacles for certain obese individuals are insurmountable and, as such, that no obese person should ever be asked to make informed, rational choices. Yet, incredibly, each writer’s new book offers dietary instruction. They advocate as well for continued research into the science of nutrition as it relates to obesity. Excellent! One wonders, however, what desirable interventions could possibly result that demand no measure of personal responsibility?
Of course some of us are biologically predisposed to obesity—myself included. Why should it surprise us that severely excessive adiposity results from any number of physical problems or abnormalities? And even among the obese, some solutions will prove more difficult than others. Nevertheless, well-intentioned, science-minded commentators shouldn’t try to convince us that obesity can’t be overcome until the evidence clearly confirms as much.
Impressionable yet intelligent, motivated children deserve far more forthright and inspiring counsel. In truth, obesity can be and often is effectively confronted, and obese children especially deserve the chance to regard their situation as an opportunity for accomplishment, and not as an excuse for regression to mediocrity.
(1) Standard BMI categories, calculated as weight in kilograms divided by height in meters squared, were reported in 1997 from the World Health Organization Consultation on Obesity and adopted in 1998 by the American National Heart, Lung, and Blood Institute. In her team’s study, Flegal used the latter organization’s current terminology: underweight (BMI of 18.5), normal weight (18.5-25), overweight (25-30), and obese (≥30). More specifically, she also defined grades 1, 2, and 3 obesity as corresponding to BMIs of 30-35, 35-40, and ≥40, respectively. All BMI categories are controversial, however, because they fail to differentiate between lean muscle mass and fat mass or subcutaneous fat (less dangerous) to visceral fat (more dangerous).
(2) But for a sociologist’s critical examination of how obesity has come to be defined as a social crisis of epidemic proportions, see Boero, Natalie. 2012. Killer Fat: Media, Medicine, and Morals in American “Obesity Epidemic.” Rutgers University Press.
Akbaraly, T., Sabia, S., et. al. 2013. Does overall diet in midlife predict future aging phenotypes? A cohort study. Am. J. Med. 126(5): 411-419.e3.
Estruch, R., Ros, E., et. al. 2013. Primary prevention of cardiovascular disease with a Mediterranean diet. N. Engl. J. Med. 368: 1279-1290.
Flegal, K.M., Kit, B.K., et. al. 2013. Association of all-cause mortality with overweight and obesity using standard body mass index categories. JAMA 309(1): 71-82.
Gillman, Mathew W., and Poston, Lucilla. 2012 Maternal Obesity. Cambridge University Press. 4-5.
Heymsflield, S.B. and Cefalu, W.T. 2013. Can overweight as defined by BMI actually have a protective association with mortality? JAMA 309(1): 87-88.
Hughes, V. 2013. The big fat truth. Nature 497: 428-430.
Kerwin, D.R., Zhang, Y., et. al. 2010. The cross-sectional relationship between body mass index, waist-hip ratio, and cognitive performance in postmenopausal women enrolled in the Women’s Health Initiative. J. Am. Ger. Soc. 58(8): 1427-1432.
Orlich, M.J., Singh, P.N., et. al. 2013. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA Intern. Med. DOI: 10.1001/jamainternmed.2013.6473. (published online June 3, 2013.)
Zuk, Marlene. 2013. Paleofantasy: What Evolution Really Tells Us About Sex, Diet, and How We Live. NY: W.W. Norton & Company.