Fat Cell Numbers Stay Constant in Adults

After your teen years, the number of fat cells in your body probably stays the same for the rest of your life, even if you gain or lose weight, according to a new study. The fat cells simply get bigger or smaller as your weight changes. The findings may help to explain why it can be so hard for some people to drop pounds and keep them off.

NIH-funded scientists developed a new technique to estimate the age of fat cells. Then they analyzed fat cells removed from adults during liposuction or other procedures. The researchers discovered that about 10% of fat cells die and are replaced each year, with the total number of cells holding steady.
The investigators then looked at how fat cell numbers change across the lifespan. They found that overweight children seem to add on more fat cells than normal-weight kids, and fat cell numbers quickly climb through the teen years. But during adulthood, the number of fat cells levels off and stabilizes.

Finally, the scientists looked at how big weight changes affect fat cells. When normal-weight men gained a lot of weight, their fat cells enlarged but the total number of cells stayed constant. When they later lost weight, their fat cells shrank but did not vanish. Likewise, people who lost weight after stomach-stapling surgery had the same number of fat cells 2 years later. The cells, though, were smaller because they contained less fat, or lipids.

“If you are overweight and you lose weight, you still have the capacity to store lipids because you still have the same number of fat cells,” says Dr. Bruce Buchholz, a scientist at Lawrence Livermore National Laboratory in California. “That may be why it’s so hard to keep the weight off.”