Two people walk into the doctor’s office. One is a young woman, aged 24, who seems relatively healthy and plays soccer on weekends. The other is a large 32-year-old man who suffers from hypertension and sleep apnea. The woman is five foot five, about 190 lb.; the man is six feet tall, 265 lb. Under the classic definition, both are “obese,” with a Body Mass Index of 30 or more (BMI is a ratio of weight to height). You don’t have to be a doctor, though, to realize that both patients probably have a different set of health risk factors—and require very different interventions as a result.
In most Western countries, roughly one-fifth of the adult population is obese, a condition that carries with it a well-known set of risks, from heart disease and diabetes to some cancers. But not all obesity is equal: beyond excess weight, many factors influence health, from fat distribution (so-called “visceral fat,” which packs around the waistline, is the most dangerous), to diet, exercise and even a patient’s genes. “Size is health in many people’s minds, but it shouldn’t be,” says Dr. Arya Sharma, scientific director of the Canadian Obesity Network and chair for obesity research and management at the University of Alberta. “Skinny people can be unhealthy, and [larger] people can be healthy over a vast range of BMIs.” Research from Sharma, and others, has experts reconsidering the definition of “obesity” as we know it.
The patients above are described in a recent paper by Sharma and Dr. Robert Kushner, a professor at Northwestern University’s Feinberg School of Medicine. In it, they note the shortcomings of current methods used to clinically evaluate obesity in individuals. For example, patients “with the same BMI value can have an almost twofold difference in total body fat,” they write. Even those who lose some weight don’t necessarily improve their “overall health or functioning.” Other factors aren’t taken into account: cardiorespiratory fitness, for example, can hugely modify the dangers of having a high BMI.
In the paper, Sharma and Kushner propose a new way to evaluate obesity. Dubbed the Edmonton Obesity Staging System, it has five stages of obesity, from 0 to 4; those at the lowest stage have no apparent obesity-related risk factors or limitations, while those at stage 4 suffer from severe disabilities. At every stage, the recommended treatment is vastly different: for that 24-year-old woman, (who’d be at stage 0), counselling on healthy eating and exercise would be recommended to prevent further weight gain. Our male patient (a stage 2) would be considered for obesity treatments, including drugs and surgery. The system is meant to complement other tools like BMI and waist circumference, says Sharma. “We’re trying to get at, ‘Why are you this big?’ ”
That question, it seems, is crucial. “Weight isn’t just a reflection of habits and character; there’s a biological system that regulates it,” says Paul Ernsberger, an associate professor of nutrition at Cleveland’s Case Western Reserve University School of Medicine. Extra pounds brought on by a bad diet, he says, are “worse for you, pound for pound,” than having a genetic predisposition toward being heavy. Ernsberger showed this by feeding naturally thin rats a high-sugar, high-fat diet, and comparing them to rats that were naturally obese. The formerly thin ones, he found, had more dangerous visceral fat packed around their organs, as well as more risk factors including high blood pressure and insulin resistance.
It could help explain why some obese people suffer from a host of health complications, while others appear to be reasonably healthy and fit. Obesity is an established risk factor for cardiovascular disease, but a surprising number of heavy individuals seem to have few or no other risk factors. In a study of 5,440 adults, a team from the Albert Einstein College of Medicine in New York found just over 51 per cent of overweight people, and 32 per cent of obese, had healthy levels of blood sugar, cholesterol, and other factors linked to heart disease. This could stem from “genetic differences between obese people,” says Dr. Swapnil Rajpathak, one of the researchers. Those at risk may have more visceral fat around their organs. Environmental factors, like diet and exercise, also play a role. “Within the obese population, not everyone has bad outcomes,” he says.
And within the normal weight population, clearly, not all outcomes are good: almost one-quarter of people with healthy BMIs were at risk of developing heart disease, that same study showed. Even thin people can carry an excess of visceral fat around the waistline, putting them at risk for everything from depression to some types of cancer. Jimmy Bell, a researcher at Imperial College in London, calls these people “thin outside, fat inside”: they have healthy BMIs, he says, but “the characteristics of an obese person.”
The obesity epidemic, it seems, isn’t so cut and dried. “We need to stop saying, ‘Everyone with a BMI over 25 needs to lose weight,’ ” says Christina Sherry, a nutritional science research fellow at the University of Illinois. “If you’re trying to lose 20 lb., that stress in itself can cause more [health] complications than the weight you’re trying to lose.”
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