A little extra padding around the hips and thighs may be a good thing, at least if you're of normal weight. And just because you're lean, it doesn't mean you're healthy.
A new analysis suggests that lean people who tend to carry fat in their hips and thighs may be at lower risk of heart disease and diabetes than those who tend to carry fat elsewhere in their body.
The researchers hypothesize that problems with the way lean people store fat in their lower body could play an important role in their risk of metabolic diseases, such as heart disease and diabetes.
The study focused on people who are lean, yet "metabolically unhealthy." That is, they have a body mass index (BMI) in the normal range, but they have at least two risk factors for heart disease and diabetes. For example, they might have high blood pressure or insulin resistance (when the body does not respond properly to the hormone insulin). About 20 percent of normal-weight people are metabolically unhealthy, the researchers said. [5 Diets That Fight Diseases]
These metabolically unhealthy lean people are at particularly high risk for heart disease, diabetes and early death — even more so than some obese people. Earlier studies have found that, compared with normal-weight people (defined by a BMI of 18.5 to 24.9) who are metabolically healthy, those who are metabolically unhealthy have a 300 percent higher risk of heart problems or early death. In contrast, obese people who don't have any of the typical risk factors for heart disease and diabetes are only about 25 percent more likely to experience early death or heart problems, compared with normal-weight people who are metabolically healthy, the researchers said.
For the new analysis, researchers in Germany analyzed information from nearly 1,000 people (including normal weight, overweight and obese people) who underwent tests to determine their precise body fat mass and fat distribution. All of the participants were at increased risk of heart disease or diabetes, based on their weight, a family history of diabetes or higher-than-typical glucose levels.
They found that, among normal-weight people, the biggest predictor of unhealthy metabolism was a low accumulation of fat in the lower body. In other words, more fat in the lower body appeared to be protective against metabolic problems for normal-weight people.
This may be because, when fat is stored in the lower body, it stays put; but if it isn't stored in the lower body, it could end up in more "dangerous" places, such as around the heart or liver, the researchers said.
"The hips and thighs offer 'safe storage' for fat, stopping it from getting into the blood and reaching the organs," study co-author Norbert Stefan, of the University Hospital Tübingen in Germany, told the Daily Mail.
If a normal-weight person has at least two metabolic risk factors, they should be checked for metabolic diseases, such as fatty liver disease or atherosclerosis (when the arteries harden and narrow due to plaque buildup), so that treatment can be started early in the disease course, the researchers recommended.
In addition, it's possible that drugs called thiazolidinediones may be particularly helpful for lean people with diabetes or heart disease, the researchers said. These medications help the body store fat in fat cells, so they may help metabolically unhealthy lean people properly store fat in their lower body. However, more studies are needed to prove this, the researchers said.
Finally, future studies should work to better understand the factors that put lean and obese people at risk for metabolic diseases. This could lead to more tailored treatments for metabolic diseases, the researchers said.
The study was published Aug. 1 in the journal Cell Metabolism.
Original article on Live Science.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.