Obesity, Heart Disease Risk Studied
< Aug. 13, 2008 > -- Two new studies released this week provide a twist of irony on the subject of obesity: Some obese people do not seem to be at increased risk for heart disease, while some normal-weight people have a number of heart disease risk factors.
The two reports were published in the Archives of Internal Medicine.
"The prevalence of obesity is increasing worldwide, and this epidemic is accompanied by a high incidence of type 2 diabetes mellitus and cardiovascular disease," the study authors say. Research indicates that in addition to overall obesity, the way body fat is distributed may influence risk for heart disease and diabetes. For instance, individuals with fat within the abdominal cavity - estimated by measuring waist size - appear to be at higher risk for insulin resistance (a pre-diabetic condition that occurs when the body fails to respond to the hormone insulin) and for having an unhealthy cardiovascular risk profile.
In the first study, German researchers analyzed 314 people, ages 18 to 69, and divided them into four groups: normal weight, overweight, obese but still sensitive to insulin, and obese with insulin resistance.
People in the overweight and obese groups had more total body and visceral fat (abdominal fat around the organs) than those with normal weight. But obese people with insulin resistance had more fat within their skeletal muscles and their livers than obese people without insulin resistance.
Obese people with insulin resistance also had thicker walls in the carotid arteries, an early sign of narrowing of the arteries - a condition called atherosclerosis.
Insulin sensitivity and artery wall thickness were the same in obese people without insulin resistance and in normal-weight people.
"In conclusion, we provide evidence that a metabolically benign obesity can be identified and that it may protect from insulin resistance and atherosclerosis," Dr. Norbert Stefan and colleagues at the University of Tubingen say. "Furthermore, our data suggest that ectopic (misplaced) fat accumulation in the liver may be more important that visceral fat in the determination of such a beneficial phenotype in obesity."
In another study in the same issue of the journal, US researchers assessed body weight and cardiometabolic abnormalities (including high blood pressure, elevated triglycerides, and low levels of "good" high-density lipoprotein [HDL] cholesterol) in 5,440 adults who took part in the National Health and Nutritional Examination Surveys between 1999 and 2004.
People with either no or only one abnormality were considered metabolically healthy, while those with two or more abnormalities were metabolically abnormal.
"Among US adults 20 years and older, 23.5 percent (approximately 16.3 million adults) of normal-weight adults were metabolically abnormal, whereas 51.3 percent (approximately 35.9 million adults) of overweight adults and 31.7 percent (approximately 19.5 million adults) of obese adults were metabolically healthy," says Rachel P. Wildman, Ph.D., of the Albert Einstein College of Medicine in the Bronx, New York, and colleagues.
Normal-weight adults with metabolic abnormalities tended to be older, less physically active, and have larger waists than healthy normal-weight adults, the study found. Obese people with no metabolic abnormalities were more likely to be younger, black, more physically active, and have smaller waists than those with metabolic risk factors.
"These data show that a considerable proportion of overweight and obese US adults are metabolically healthy, whereas a considerable proportion of normal-weight adults express a clustering of cardiometabolic abnormalities," the researchers conclude. "Further studies into the behavioral, hormonal, or biochemical and genetic mechanisms underlying these differential metabolic responses to body size are needed and will likely further the identification of possible obesity intervention targets and improve cardiovascular disease screening tools."
Dr. Lewis Landsberg, of the Northwestern University Comprehensive Center on Obesity in Chicago, says, "Both reports emphasize the benign nature of fat accumulation outside the abdomen."
"In both studies, the detrimental effect of visceral fat accumulation and its surrogate, waist circumference, were clearly demonstrated, confirming older studies showing that waist circumference is a risk factor even in normal-weight individuals," he says.
The studies show it is important to calculate body mass index and measure waist circumference when assessing cardiovascular risk in overweight and obese patients, Dr. Landsberg notes.
Always consult your physician for more information.
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Overweight and obesity together represent the second leading preventable cause of death in the United States. Obesity is a serious, chronic disease that can inflict substantial harm to a person’s health.
Overweight and obesity are not the same; rather, they are different points on a continuum of weight ranging from being underweight to being morbidly obese. The percentage of people who fit into these two categories, overweight and obese, is determined by Body Mass Index (BMI).
The US Surgeon General has declared that overweight and obesity have reached epidemic proportions in this country. About 17 percent of children between the ages of six and 19 are overweight. Public health officials say physical inactivity and poor diet are catching up to tobacco as a significant threat to health. Currently, about 35 percent of women and 33 percent of men are considered obese.
BMI is a measure of weight proportionate to height. BMI is considered a useful measurement of the amount of body fat. Occasionally, some very muscular people may have a BMI in the overweight range. However, these people are not considered overweight because muscle tissue weighs more than fat tissue. Generally, BMI can be considered an effective way to evaluate whether a person is overweight or obese.
According to the National Heart, Lung, and Blood Institute (NHLBI), a BMI from 18.5 to 24.9 is considered normal while a BMI of more than 25 is considered overweight. A person is considered obese if the BMI is greater than 30 and morbidly obese if the BMI is 40 or greater. In general, after the age of 50, a man's weight stabilizes and even drops slightly between the ages of 60 and 74. However, a woman's weight continues to increase until age 60 and then begins to drop.
Another measure of obesity is the waist-to-hip ratio (WHR). The WHR is a measurement tool that looks at the proportion of fat stored on the waist, and hips and buttocks. The waist circumference indicates abdominal fat. A waist circumference over 40 inches in men and over 35 inches in women may increase the risk for heart disease and other diseases associated with being overweight.
Obesity has a far-ranging negative effect on health. Each year obesity-related conditions cost over 100 billion dollars and cause an estimated 112,000 premature deaths in the US. The health effects associated with obesity include, but are not limited to, the following:
- high blood pressure
- diabetes
- heart disease
- joint problems, including osteoarthritis
- sleep apnea and respiratory problems
- cancer
- metabolic syndrome
- psychosocial effects
Consult your physician with questions regarding healthy body weight.
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