December 28, 2016
Being fat is OK
Continuing from my post here.
Top Cardiologist Blasts Nutrition Guidelines (the incidence of cardiovascular disease in the PURE population increases as carbohydrate intake (as a percentage of total calories) rises.)
This article: Survival of the fattest: Why we’re wrong about obesity
- 05 May 2014 by Samantha Murphy
Weight tells you far less about a person’s health than you might think (Image: Richard I’Anson/Getty) Can you be fat and fit? Everything we think we know about obesity may be wrong – sometimes it be could actually be good for you
In 2002, cardiologist Carl Lavie began to see a confusing trend. The people he was treating for heart failure were living longer if they were obese or overweight than if they were thin. How could that be right? Obesity is notoriously bad for your heart and every other part of your body.
In the US, obesity is one of the biggest causes of preventable deaths after smoking. Worldwide, it has been linked to chronic diseases like hypertension, stroke, heart disease and type-2 diabetes. Even so, the world keeps getting fatter, a trend that may mean we will all be obese by mid-century, propelling those of us in the West ever closer to the first drop in our life expectancy since 1800.
But how much of this is true? Lavie wasn’t the only one to notice some troubling inconsistencies in the seemingly simple story. Under fresh scrutiny, conventional wisdom about the obesity epidemic is beginning to unravel, prompting some medical professionals to call for changes to everything from public policy to healthcare training.
It is small wonder we have become so obsessed with our weight. Between 1980 and 2008, body mass index (BMI) – a measure of obesity that divides weight by height squared – rose all over the world. Obesity rates nearly doubled, rising most strikingly in the US. It wasn’t hard to see where it was all heading. In the title of a widely cited paper investigating the progression and cost of the US obesity epidemic, the authors asked: “will all Americans become overweight or obese?” Yes, they concluded: by about 2050.
So it came as a surprise when, in the early 2000s, epidemiologist Katherine Flegal began to see evidence that obesity rates had stopped rising. In study after study, Flegal, who works at the Centers for Disease Control (CDC) in Hyattsville, Maryland, found that instead of continuing relentlessly upwards, obesity rates had levelled off.
Not everyone was convinced, but this was no flash in the pan. Flegal and her team continued to replicate their research and, in a study released in 2012, they announced that the prevalence of obesity in the US has failed to increase in any significant way since at least 2008 (JAMA, vol 307, p 491). It appears to have flatlined around the 34 per cent mark in both adults and adolescents (see “Obesity plateau”). And this “obesity plateau” is not limited to the US: similar trends and even declines have been described in other developed countries over the past 10 to 15 years.
Because the research is still in the early stages, no one is sure what is causing the obesity plateau. But some competing theories are emerging. Researchers at the University of Jena in Germany point to small studies showing the success of better food and exercise programmes. Whatever the reason, the idea that obesity rates will rise unchecked seems to be in need of revision.
Where does that leave the 34 per cent of people still considered obese? In 2004, the CDC warned that obesity could soon be second only to smoking as a cause of preventable deaths. Of course, it won’t be the extra pounds that kill you. What supposedly shortens your life is the link between obesity and the development of a host of diseases including type 2 diabetes, heart disease, cancer and rheumatoid arthritis.
Over the past 10 years, however, some of these links have been called into question as well. The most surprising of them is the one that always seemed the most intuitive: the relationship between obesity and heart disease. “Over a decade ago, I would have thought my heavy patient who just had a heart attack would have been worse off than my thin patient who just had a heart attack,” says Lavie, who is a cardiologist at the Ochsner Medical Center in New Orleans, Louisiana. “But it’s exactly the opposite.” Heart disease patients classified as lean had almost double the mortality rate of those ranked overweight and even obese.
Startled by his own anecdotal findings, Lavie began to dig into the literature. He found numerous large-scale studies that backed up his observations: some overweight patients with cardiovascular disease have better outcomes than their thinner counterparts. One of the largest, a 2012 study of 64,000 Swedish people with heart disease, found that obese or overweight participants had a reduced risk of dying compared with those of normal weight (European Heart Journal, vol 34, p 345). Underweight patients, meanwhile, upped their risk of death by a factor of three. In the paper, the authors went so far as to suggest that prescribing weight loss after diagnosis of heart disease might be a bad idea.
Heart conditions were far from being the only ailments where extra padding seemed to be an advantage. Equally surprising was the clear link between obesity and the fate of people with type 2 diabetes. Among others, a Northwestern University study of 2625 people recently diagnosed with type 2 diabetes found that normal-weight people were almost twice as likely to die over the period of the study as their overweight and even obese counterparts.
Next came rheumatoid arthritis and kidney disease. Over and over, the same pattern cropped up: people diagnosed with many medical killers fared better in the long run if they were overweight or even mildly obese than if their weight was normal. “Yes, this even remains true when researchers rule out weight loss attributable to other pre-existing illnesses such as cancer,” says Lavie. To be clear: becoming overweight is not a fitness goal – a sedentary lifestyle, poor diet and a BMI of 40 will not lead you to health. However, once you are overweight, it seems, being healthy is not synonymous with shedding pounds. Fatter people are more likely to survive many diseases. The phenomenon has been observed so often that it has earned the name “the obesity paradox”.
But how can flab be good for you in any way? One tentative theory doing the rounds is that body fat contains anti-inflammatory compounds and extra energy that can bolster the body’s defences against the ravages of disease. More specific experiments have pointed to the hormone leptin, which is stored in fat, suggesting that some extra fat may have protective effects for people with heart failure (Circulation Heart Failure, vol 2, p 676). People with more fat have access to these “extra reserves” stored within. In any case, the conflicting studies meant that, in 2005, even the CDC backed away from its earlier contention that obesity could be the leading cause of death after tobacco.
But last year, the plot thickened still further: could being overweight be healthier not just for sick people – but for all of us? In a meta-analysis that investigated the relationship between BMI and health in 2.88 million people, a CDC team led by Flegal – who had introduced the obesity plateau – showed that the relationship between health and weight was U-shaped rather than linear (see “Fat and fit”). That’s to say, being overweight or even mildly obese was associated with a lower risk of dying – from any cause – than being either underweight or extremely obese.
Flegal’s research started a firestorm of controversy. In a study of people with diabetes published last January, Deirdre Tobias of Harvard University found no similar benefits. When Tobias redid her analysis, focusing as Flegal had on death by any cause instead of diabetes, she found Flegal’s U-shaped curve. However, Tobias says taking out smokers changed the shape of the curve to a J. “There is no advantage for being overweight or obese,” she says, but her new curve does not clearly demonstrate the linear relationship between weight and health implied by BMI. Tobias’ group thinks the obesity paradox can be entirely chalked up to poor research methods. But can so many studies be so wrong? Or are the obesity plateau and the obesity paradox signs that it is time to abandon a metric whose inaccuracy verges on scandal?
The BMI system has been incorrectly used from the start (see “Why BMI?“). Its oft-cited flaws are almost too numerous to count.
First, whether applied to individuals or populations, BMI is a consistently unreliable indicator of actual fat. It fails to account for where fat is located on the body – according to several analyses, it is abdominal obesity, not total body fat, that truly predicts whether a person will develop cardiovascular problems or cancer. It also famously fails to distinguish between fat and muscle.
This familiar critique – that BMI cannot differentiate between Arnold Schwarzenegger and the Michelin Man – is often dismissed. After all, not many people who have an obese BMI look like Arnold Schwarzenegger. But the dismissal masks a subtler point: in many cases a person classified by BMI as overweight or “grade 1” obese (adjacent to the overweight range) may be metabolically healthier than their normal-weight counterpart simply as a result of better fitness. According to the standard BMI categories, however, this person is indistinguishable from a severely obese person with minimal fitness.
Worse, when an overweight person gains muscle, they change their health for the better but often change their BMI for the worse. Occasionally this even bumps them into the “obese” category. And this category is wildly over-inclusive, encompassing any BMI over 30, which conflates a range of weights that stretches, in theory, to infinity. Flegal, for one, thinks this is the confounding factor in many of the studies. In her 2013 findings, she says, she saw major differences in health between people classified as “grade 1” obese and people whose BMI was closer to 40. “Grade 2 to 3 obesity was significantly associated with excess mortality but grade 1 obesity was not,” she says. Most studies that rely on BMI, however, rarely make the distinction. Healthcare providers tend to ignore it as well.
This is why BMI consistently fails to account for healthy obese people and unhealthy thin people, two groups that keep turning up in new research. For example, in a 2013 study of 43,000 people that investigated the link between obesity and cardiovascular disease, 46 per cent of the obese population were found to be metabolically healthy, having none of the high blood pressure, high cholesterol and insulin resistance normally associated with obesity. This “healthy obese” group had the same chance of dying from cardiovascular disease or cancer as their normal-weight counterparts who were also metabolically healthy (European Heart Journal, vol 34, p 389). Based on the size of their 25-year study, the authors speculate that this state of being metabolically healthy but obese is common in the general population. Alongside the steadily growing body of work describing the obesity paradox, this reveals that BMI doesn’t even necessarily work as a proxy for the general health of a population.
“Weight is the wrong thing to be paying attention to,” says Linda Bacon, a nutritionist at the University of California, Davis. Lavie agrees. “There’s just not that much evidence that you’re gaining a lot by losing weight,” he says. So for anyone between 18.5 and 35 on the BMI chart, he says the key is physical fitness, not weight loss. “If I’m sitting with a mildly obese patient who just had a heart attack, they can actually have a good prognosis, or even a better prognosis than a thin person, if we can get them to become more physically fit,” he says. Bacon and Lavie are far from the only ones coming to this conclusion.
No size fits all
This represents a paradigm shift for cardiologists, who have tended to recommend weight loss to anyone whose BMI is above normal. It is a controversial position. After all, one concern raised frequently about Flegal’s work is that it could undermine policies to curb obesity rates. If everyone starts to think of higher weights as normal, parents might no longer understand that their overweight children have a weight problem, England’s chief medical officer recently told New Scientist.
However, research is beginning to show that the focus on BMI may not be helping. In a study published in February, researchers from the Johns Hopkins School of Medicine in Baltimore, Maryland, found that patients who felt their doctor judged them for their weight were more likely to attempt weight loss, though not more likely to succeed.
Indeed, the fixation on BMI could be causing actual harm, discouraging overweight and obese people from seeing their doctors in the first place. A team of researchers from Columbia University in New York identified weight-related barriers such as fear, modesty, insensitivity and lack of facilities, all of which were discouraging obese women from going for potentially life-saving mammograms and smear tests (Obesity, vol 20, p 1611).
The deeper question may be – why is anyone still using BMI? At least five alternatives have been proposed, ranging from a subtler mathematical formula to a waist-to-height system that better reflects actual risk of disease. At this point, however, no public health agencies have any plans to switch to another measure. Part of the problem is that BMI is alone in offering the official cut-offs that are so useful in making easy assessments.
To minimise the damage, in the shorter term, many recommend that doctors use BMI with more care. For young people, for example, classic BMI metrics appear to be relevant, but for the elderly in particular, Lavie thinks the BMI guidelines are misguided; research is accumulating to show that obesity in this population is associated with a lower, not higher, risk of death. Likewise, BMI does not apply equally to all races, and should be different for the genders – as the NIH understood in its original version of the guidelines (see “Why BMI?“). And under some circumstances, people with certain diseases including cancer and HIV might even consider gaining weight beyond the recommendations set by BMI.
Others wonder whether health concerns are truly at the heart of the obesity panic. “We live in a society that condones fat shaming,” says Abigail Saguy, a sociologist at the University of California in Los Angeles. “There remains a kind of social acceptance for this type of judgment, a lack of empathy.” Saguy notes that she has seen no evidence that discrimination, stigma and shaming is motivating in terms of weight loss. “It has no positive effects,” she says. The real public health epidemic, she suggests, is discrimination against the overweight and obese: “less social acceptance of weight-based discrimination and shaming could potentially save lives.” This article appeared in print under the headline “Flabbergasted”
So where did we get the idea that general health and BMI are closely linked? The system was developed by a Belgian statistician in 1832, more out of academic curiosity about what constitutes the “normal” person than interest in obesity.
In the 1940s, life insurance companies adapted it as an easy way to determine policy risk. In 1985, it was adopted by the US National Institutes of Health (NIH), and then in 1995 by the World Health Organisation, to estimate obesity in large populations.
Even these guidelines have not been written in stone. In 1998 the NIH pushed the definition of obesity to 30 from 27 and added a new category – overweight – instantly classifying millions of previously “fit” Americans as fat. It also consolidated previously different guidelines for men and women.
No one ever suggested that it should be a proxy for a single individual’s health – its inventor warned explicitly against doing so.
But that is exactly how we use it today: anyone whose statistics stray outside the normal BMI range is advised to lose weight. Context-free online BMI calculators proliferate. There is good reason to rethink this approach (see main story).
Samantha Murphy is a journalist based in Lancaster, Pennsylvania