Obesity May Turn Muscles Into Fat

The muscles of obese people may welcome fat with open arms, new research shows.

Severely obese people have three times as much of a fat-building enzyme called SCD1 in their muscle cells than lean people, scientists report.

That could be one reason why it’s often hard to permanently lose weight through diet alone.

“While these findings may be somewhat discouraging news for those wishing to reverse obesity through dietary interventions, they also highlight the importance of exercise,” says researcher Deborah Muoio, PhD, in a news release.

Exercise is known to produce big changes in muscle metabolism, explains Muoio. She works at Duke University’s Sarah W. Stedman Nutrition and Metabolism Center.

The study appears in Cell Metabolism.

Fat-Friendly Muscle

The researchers studied muscle cells from lean and obese women. The obese patients were matched to lean patients of the same age and race.

The lean women had a BMI (body mass index) of 25 or less. The obese women in the study had a BMI of 35 or more. According to CDC provides guidelines for BMI,18.5 to 24.9 is normal, 25.0 to 29.9 is overweight, and 30 or more is considered obese.

First, the researchers checked SCD1 levels in participants’ muscles. They found three times as much SCD1 in the muscles of the obese women studied.

Next, the scientists did some lab tests that made the lean women’s muscle cells produce more SCD1. That pushed those muscle cells towards fat accumulation, the study shows.

Gene Link

Exactly why obesity and SCD1 went hand in hand isn’t known. It’s not clear which came first, the obesity or the rise in SCD1. Did the obesity cause SCD1 to rise, or vice versa?

The researchers outline one possibility.

The body’s recipe for making SCD1 is stored in genes. Becoming obese might switch on those genes, ramping up SCD1 production and programming muscles to fatten up.

Once those genes are on, they may stay on, the researchers note, citing studies of animals and research on big groups of people (epidemiological studies).

Possible Solutions

It might be possible to create drugs that target muscle SCD1, the researchers note. They also want to see if physical activity can help lower SCD1 or modify its effect in obese people.

If you don’t want to wait for those results, know that physical activity is recommended across the board for many reasons besides lowering weight (including heart and bone health). Get your doctor’s blessing before starting a new fitness program, especially if you’ve been overweight or idle.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Hulver, M. Cell Metabolism, October 2005; vol 2: pp 251-261. News release, Cell Press. CDC web site.