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Study Finds Leptin Test Could Improve Accuracy for Estimating Body Fat

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May 4, 2012

A blood test for the hormone leptin may be an effective way to gauge how much excess fat a person is carrying, according to researchers. In some people, checking the level of leptin in the bloodstream may be more accurate than relying solely on the traditional body mass index (BMI) to assess body fat, the researchers reported in the online journal PLoS ONE published April 2, 2012.

It is well known that obesity contributes to many diseases, including diabetes and heart disease, but what is actually causing the damage is excess body fat. Experts say a person is obese if more than 25-30% of their total body weight is made up of fat. To tackle the obesity epidemic, there is a need for a way to better estimate how much of a person's body is fat, rather than other tissues, such as bones and muscles.

Obesity remains a major public health concern in the U.S. The Centers for Disease Control and Prevention reports that in 2010 every state in the U.S. had a prevalence of obesity over 20% and currently more than one-third of adults and 17% of children and teens in this country are obese. Presently, the way that many people are classified as being obese is using body mass index, but that may not be the best method.

That's where leptin may be useful. Leptin is a hormone that is thought to play a role in the regulation of appetite, energy production, and metabolism. It is produced by the fat-storing cells of the body – the more fat tissue a person has, the higher the level of leptin in the bloodstream.

In this cross-sectional study of over 1,000 adults, the researchers measured both the leptin level and the BMI, a score calculated from the person's height and weight that is commonly used to estimate body fat content. Then they compared these results with those of an X-ray test called dual-energy x-ray absorptiometry (DXA or DEXA). DEXA is most commonly known as a test for bone density but is also used to measure the amount of muscle and fat in the body.

The study showed that in some people, the BMI score was misleading. It found that people with less muscle than average may have hidden fat not reflected by the BMI score. In such people, particularly older women, a leptin test would reveal the true level of body fat. On the other hand, those with large muscles or very dense bones may be falsely classified as obese by the BMI. In the study, 25% of men and 48% of women were misclassified by BMI. Leptin level, however, was closely related to the amount of fat measured by the DEXA scan.

While leptin measurements may be a better indicator of body fat than BMI, it is still too early to tell whether leptin will be a useful clinical tool in the management of obesity. Leptin values show considerable biological variability. Measurements of leptin in the same person on different days can result in values that differ significantly. Therefore, a single leptin measurement would be inadequate to accurately predict percent body fat. For this reason, more research is needed to better identify the role of leptin and its potential value in managing obesity and the risk of obesity-related disease.

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used. To access online sources, copy and paste the URL into your browser.

Nirav R. Shah, Eric R. Braverman. Measuring Adiposity in Patients: The Utility of Body Mass Index (BMI), Percent Body Fat, and Leptin. PLoS One. Published April 2, 2012. Available online at through Accessed April 2012.

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