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‘Fitness and Fatness’: Arnold School study shows that not all obese people have same prognosis
September 12, 2012
A study from the University of South Carolina’s Arnold School of Public Health finds that people can be obese but metabolically healthy and fit, with no greater risk of developing or dying from cardiovascular disease or cancer than normal weight people, according to one of the largest studies to have investigated this, published online in the European Heart Journal.
The findings show a subset of obese people who are metabolically healthy. They don’t suffer from conditions such as insulin resistance, diabetes and high cholesterol or blood pressure. They also have a higher level of fitness, as measured by how well the heart and lungs perform, than other obese people. Being obese does not seem to have a detrimental effect on their health, and doctors should bear this in mind when considering what, if any, interventions are required, say the researchers.
“It is well known that obesity is linked to a large number of chronic diseases, such as cardiovascular problems and cancer. However, there appears to be a subset of obese people who seem to be protected from obesity-related metabolic complications,” said Dr. Francisco Ortega, the study’s lead author.
“They may have greater cardio-respiratory fitness than other obese individuals, but, until now, it was not known the extent to which these metabolically healthy but obese people are at lower risk of diseases or premature death,” said Ortega, a research associate in the department of physical activity and sport at the University of Granada (Spain) and at the department of biosciences and nutrition at the Karolinska Institutet in Stockholm, Sweden.
The project and investigation took place at USC’s Arnold School, under the direction of Dr. Steven Blair, a professor in the department of exercise science and the department of epidemiology and biostatistics. Blair is responsible for the long-running “Aerobics Center Longitudinal Study” (ACLS), which provided the 43,265 participants for this current analysis.
The participants were recruited to the ACLS between 1979 and 2003. They completed a detailed questionnaire, including information on their medical and lifestyle history. They had a physical examination that included a treadmill test to assess cardio-respiratory fitness and measurements of height, weight, waist circumference and their percentage of body fat. Blood pressure, cholesterol and fasting glucose levels also were measured. The study participants were followed until they died or until the end of 2003.
Ortega and his colleagues found that 46 percent of the obese participants were metabolically healthy. After adjusting for several confounding factors, including fitness, the metabolically healthy but obese people had a 38 percent lower risk of death from any cause than their metabolically unhealthy obese peers, while no significant difference was seen between the metabolically healthy but obese and the metabolically healthy, normal weight participants. The risk of developing or dying from cardiovascular disease or cancer was reduced by 30 to 50 percent for the metabolically healthy but obese people. There were no significant differences observed between the metabolically healthy but obese and the metabolically healthy, normal weight participants.
“Our study suggests that metabolically healthy but obese people have a better fitness level than the rest of obese individuals,” Ortega said. “Based on the data that our group and others have collected over the years, we believe that getting more exercise broadly and positively influences major body systems and organs and consequently contributes to make someone metabolically healthier, including obese people. In our study, we measure fitness, which is largely influenced by exercise.”
The study has two major findings. The first is that a better cardio-respiratory fitness level should be considered as a characteristic of this subset of metabolically healthy obese people. Second, once fitness is accounted for, the study shows for the first time that metabolically healthy but obese individuals have a similar prognosis as metabolically healthy normal-weight individuals, and a better prognosis than their obese peers with an abnormal metabolic risk factors, Blair said.
The researchers say their findings have important clinical implications. “The data suggest that accurate body fat measurements and fitness assessment can contribute to properly define a subset of obese individuals who do not have an elevated risk of CVD [cardiovascular disease] or cancer,” Ortega said.
Blair said the findings are significant for physicians and other health care professionals.
Physicians could assess fitness, fatness and metabolic markers to better estimate the risk of cardiovascular disease and cancer of obese patients. “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,” Blair said. “This research highlights once again the important role of physical fitness as a health marker.”
Other Arnold School researchers who worked on the study include Dr. Mei Sui in the department of exercise science and Dr. Duck-chul Lee, a post-doctoral fellow now at the University of Iowa.
