Researchers at Virginia Tech are taking a closer look at body distribution patterns to learn more about how different types of obesity influence cardiovascular physiology and overall health.
According to Kevin Davy, associate professor of human nutrition, foods, and exercise in the College of Agriculture and Life Sciences, individuals with an "apple," or abdominal, fat distribution pattern are at a substantially higher risk of developing cardiovascular and metabolic diseases compared with those with a "pear" or lower body fat distribution pattern. The apple body fat distribution pattern is typically characterized by an excess accumulation of intra-abdominal fat (or fat located around the internal organs), whereas the pear body fat distribution pattern is characterized by subcutaneous (under the skin) fat storage in the buttocks and thigh regions.
Abdominal obesity (also called intra-abdominal obesity) is associated with a number of cardiovascular and metabolic disease risk factors that cluster together in an individual, says Davy. The clustering of these risk factors is referred to as the metabolic syndrome. These risk factors synergistically increase the risk for cardiovascular disease.
"If clinical disease is not already present, then these individuals are frequently pre-diabetic and pre-hypertensive. They are on the fast track to the full clinical expression of these diseases if drug and/or lifestyle intervention is not initiated," explains Davy.
Davy and his colleagues are particularly interested in understanding how intra-abdominal fat links obesity with high blood pressure. "Individuals with excess intra-abdominal fat exhibit reduced compliance, or elasticity of the major arteries in the cardiothoracic region. This significant increases the workload of the heart. We know that reduced arterial compliance is related to a number of adverse outcomes, particularly high blood pressure," says Davy. "All the risk factors that comprise the metabolic syndrome have negative effects on blood-vessel health. Arterial stiffening is considered to be an early event in the atherosclerotic process. All of these risk factors converge to reduce the compliance of an artery."
"The ability to increase the heart rate in response to falling blood pressure, for example, appears to be blunted in individuals that have less compliant arteries. This may be related, in part, to the fact that some of the receptors that signal the brain to increase heart rate when blood pressure falls are located in the aorta and carotid arteries," explains Davy. "We think that that intra-abdominal obesity leads to arterial stiffening as a result of the risk factors clustering in the metabolic syndrome, but arterial stiffening also has direct effects on the structure and function of cardiovascular system. Over time, reductions arterial stiffness can also lead to high blood pressure."
Many researchers are trying to understand why these risk factors cluster together in the same individuals and how this clustering of risk factors alters disease risk. Davy and his colleagues are examining whether the changes in the amount of intra-abdominal fat are associated with predictable changes in the structure and function of the cardiovascular system.
With funding from the National Institutes of Heath, Davy and his multi-disciplinary team of researchers are having overweight and obese people lose weight. "Our plan is to compare those individuals with relatively large and small reductions in intra-abdominal fat with weight loss. We expect that subjects with the largest intra-abdominal fat loss will demonstrate the greatest improvement in the arterial stiffness and vice versa, says Davy. We are also interested in determining whether any observed improvement in arterial stiffness can be sustained with maintenance of weight loss."
According to Davy, the available literature would suggest that there is a correlation between the amount of intra-abdominal fat and the degree of arterial stiffening across a wide range of total body and intra-abdominal fat. However, the correlation between intra-abdominal fat and arterial stiffness may not be cause and effect, explains Davy. "It could be that a person with elevated intra-abdominal fat also has a particular genetic make-up or constitution that is also associated with stiffer arteries. We need intervention studies to further address this issue," he says.
Davy is hoping that he can verify his hypothesis that weight loss, particularly from the abdominal intra-abdominal region, will reduce arterial stiffness. He anticipates that reductions in arterial stiffness will also have a favorable impact on other aspects of cardiovascular structure and function.
Coronary artery disease is already well developed by the time someone may need to visit the emergency room for chest pain. We can detect arterial stiffening way before a person actually has the symptoms of cardiovascular disease," Davy says. "We can most effectively prevent disease by intervening early."
"The key is to avoid becoming obese in the first place," says Davy. "Preventing further weight gain should be the number one priority for individuals who are already overweight or obese." He suggests a low-fat, high-fiber diet along with plenty physical activity.