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"It is possible to be fat and fit -- but relatively few people are," said Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine. He took no part in either study.
"For the most part, the behaviors that promote fitness most effectively defend against fatness into the bargain. It is certainly possible to be thin and unhealthy, which is why health, not a particular weight, is what we should be aiming for as both individuals and a society," he said.
Both reports were published online Sept. 5 in the European Heart Journal.
For the first study, a team led by Francisco Ortega, of the department of biosciences and nutrition at the Karolinska Institute in Stockholm, collected data on more than 43,000 people who were part of the Aerobics Center Longitudinal Study.
Study participants were mostly white (98 percent), and were well-educated and worked in executive or professional positions.
Each participant answered questions about medical history and lifestyle, and took a treadmill test to evaluate their cardiovascular fitness. In addition, their height, weight, percent of body fat and waist size were measured, as well as blood pressure, cholesterol and blood sugar.
Study participants were recruited between 1979 and 2003, and followed until the end of 2003 or until they died.
The researchers found that among obese individuals, 46 percent were heart healthy and had a 38 percent lower risk of dying than those obese people who were not heart healthy.
Moreover, those healthy obese had the same reduced risk of heart disease and cancer as healthy normal-weight people, they added. Both groups had a 30 percent to 50 percent reduction in their risk for cardiovascular disease or cancer compared to obese people who were not heart healthy, the researchers found.
"Not every obese person is equally healthy/unhealthy," Ortega said. "There is a relatively large subset of obese people that are metabolically healthy, and if obesity is defined using body-fat percent (instead of body-mass index) and cardiac-respiratory fitness is taken into account, the future prognosis of metabolically healthy but obese people is similar to that of normal-weight people," he said.
Doctors should take into consideration that not all obese people have the same prognosis, Ortega said.
"Physicians could assess fitness, fatness and metabolic markers to do a better estimation of the risk of cardiovascular disease and cancer of obese patients," Ortega explained. "Our data support the idea that interventions might be more urgently needed in metabolically unhealthy and unfit obese people, since they are at a higher risk," he said.
Dr. Gregg Fonarow, a spokesman for the American Heart Association and professor of cardiology at the University of California, Los Angeles, said the study follow-up period was too short to really determine if obese people in the study were heart healthy.
"This study followed individuals for 15 years -- further studies are needed to determine the long-term health consequences of obesity in these individuals," he said.
In the second study, Dr. Oskar Angeras, a consultant cardiologist at the Sahlgrenska Academy of the University of Gothenburg in Sweden, and colleagues collected data on more than 64,000 people in the Swedish Coronary Angiography and Angioplasty Registry, who had heart disease or had a heart attack between May 2005 and December 2008.
Angeras' team found those with the lowest risk of dying after acute coronary syndrome were overweight and moderately obese, while the highest risk was among the underweight and the morbidly obese.
Conventional wisdom says losing weight improves health, but that may not be the case for obese people who have already developed heart disease, the researchers say.
"In acute coronary syndrome, the obesity paradox suggests that there could be protective mechanisms in either fat tissue or in obese patients' [individual makeup] that reduce the risk of mortality. This is of course speculative and needs further investigations," Angeras said.
"We believe that it is important to focus on secondary prevention like treating [high blood pressure] and [high fat levels in the blood], stop smoking, exercise and eat a healthy diet, which has solid evidence in literature," he added. "Weight reduction is, however, perhaps not that important in itself, more a cause of anxiety among patients."
Angeras added that the obesity paradox exists and should be recognized in health care guidelines for acute coronary syndrome.
Fonarow pointed out that multiple explanations and potential mechanisms have been advanced to explain the obesity paradox, but the exact mechanisms are not known and further studies are needed.
"Yet, patients who are obese present with acute coronary events at an age 8 to 10 years younger, compared with healthy and underweight individuals, [which] demonstrates the adverse consequences of obesity in developing cardiovascular events in the first place," Fonarow said.
And Katz added that there has long been evidence that the overall relationship between body weight and all-cause mortality, when plotted as a graph, takes the shape of a J or U, with lower mortality near the middle, and higher mortality at both the lowest and highest weights.
"But there is no paradox in this," Katz said. "Sick people lose weight, and the sickest people lose the most weight of all. Sometimes, this is the disease. Sometimes, it's the therapy -- such as cancer chemotherapy. And sometimes, it's an array of factors such as isolation, loneliness and despair. In contrast, people with a reserve of vitality, and hope, keep eating."
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