Leptin and Obesity

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April 11, 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 US 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, they said in the online journal PLoS ONE.

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

That’s where leptin comes in. Leptin 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 the new study, 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 a special X-ray test, duel-energy x-ray absorptiometry (DXA or DEXA), probably the best way to calculate how much of a person’s body is made up of fat. DEXA is commonly used to test the strength of the bones but can also be 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 people with less muscle than average may have hidden fat not picked up by the BMI score. In such people, particularly older women, a leptin test would reveal the true level of body fat. While leptin measurments may be a better indicator of body fat than BMI it is still too early to say that leptin will turn out to be more useful than the current group of measurements and factors that are used to estimate a person's future risk of having a heart attack or another form of cardiovascular disease.

Leptin hit the headlines in the 1990’s when it was given as a drug to very obese mice with abnormal metabolism. It helped the mice lose weight but has not proven to be a wonder drug for the vast majority of people needing to lose weight. 

The leptin test is currently not widely available in Australia and leptin tests are not covered by a Medicare rebate.