More than half of normal-weight Americans have a high percentage of body fat making them susceptible to several life shortening diseases including diabetes, heart disease, high cholesterol, metabolic syndrome and other metabolic disorders, according to cardiologists from the Mayo Clinic.

Body Mass Index 

The researchers defined "normal weight" by body mass index (BMI). Body Mass Index (BMI) is a measure of body fat based on height and weight that applies to both adult men and women.  BMI is a reliable indicator of total body fat, which is related to the risk of disease and death.The researchers found that people with normal BMI who had the highest percentage of body fat were also those who had metabolic disturbances linked to heart disease.

Normal Weight Obesity Defined  

The researchers use the phrase "normal weight obesity" to describe this new type of patient at risk for metabolism problems and risk factors for heart disease, but who rates as "normal" on standard weight charts. According to the researchers. "Using the term ‘normal weight obesity' is really a way of being more precise about the changing conceptualization of obesity, because the real definition of obesity is excess body fat."

They defined normal weight obesity as a condition of having a normal BMI with high body fat percentage. The Mayo team will present its study results at the American College of Cardiology's Annual Scientific Session next week in Chicago.

Study Parameters

The researchers studied 2,127 adults, equally divided between men and women, who had normal weight (BMI between 18.5 and 24.9 units). The participants' body composition was assessed, and their risk factors for metabolic and heart disease were collected by the U.S. government in its Third National Health and Nutrition Examination Survey http://www.cdc.gov/nchs/products/elec_prods/subject/nhanes3.htm.

From this data, the researchers found that normal weight obesity appears to be highly prevalent, affecting more than half of patients with a normal weight as defined by the BMI.  After controlling for age, sex and race, normal weight obesity subjects had significantly higher rates of several alterations in blood chemistry that can negatively affect heart and metabolism health. These markers of disregulation include:

• Altered blood lipid profile, such as cholesterol
• High leptin, a hormone found in fat and other tissues and is involved in appetite regulation
• Higher rates of metabolic syndrome

Significance of the Study

Heart disease remains the major cause of death and disability in westernized countries. While a focus on maintaining "a healthy weight" and a healthy diet  long been the focus  of these efforts, the study suggests the focus may need to shift from tracking weight and BMI only, and instead include measuring abdominal fat, and assessing the percentage of body fat as more reliable risk factors of heart disease.

It has been known for sometime now in the health and fitness field that the BMI does not discriminate between body fat and lean muscle, therefore it has several limitations when assessing risk.

Implications

The study demonstrates that even people with normal weight may have excessive body fat, and that these people are at risk for metabolic abnormalities that lead to diabetes and, eventually, to heart disease and possibly death.

These findings should alert doctors that body weight isn't the only way to protect against health problems caused by excess pounds, according to lead researcher Dr. Francisco Lopez-Jimenez, a cardiologist with the Mayo Clinic in Rochester, Minn. "Many of these people have metabolic abnormalities."

"If you have a normal weight, don't feel that everything is just OK," Lopez-Jimenez added.

One expert agrees that normal body weight is not synonymous with good health.
"Body weight is a very blunt instrument; it is not a reliable gauge of obesity, or health, at the individual level," said Dr. David L. Katz, director of the Prevention Research Center at Yale University School of Medicine. "For example, a muscular man may have a very high body weight, yet be perfectly fit and healthy. Many people whose body weight is in the normal range are anything but."

And some people are vulnerable to weight gain in all the wrong places, such as in and around the vital organs of the abdomen, notably the liver, Katz said.

"Even a small amount of extra fat where it matters most can wreak metabolic havoc, increasing risk for diabetes and heart disease, while leaving you with a body weight that looks perfectly innocent," Katz said. "Excess body fat in the belly is a menace, whatever your weight. This study should sensitize patients and providers alike to this concern."

Lopez-Jimenez said the study shows that just because your weight may be normal for your size, it doesn't mean you aren't at risk for several life threatening diseases such as diabetes, heart disease, high cholesterol, metabolic syndrome a precursor of diabetes and other metabolic diseases.