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.”

Long-term, uncontrolled high blood pressure puts you at risk for kidney disease. Doctors often prescribe blood pressure drugs to protect kidneys. But now a new study suggests that, in people with kidney damage from high blood pressure, even the best efforts to control blood pressure can lead to a continuing decline in kidney function. The decline seems to be gradual in some people but significant in others.

Kidney disease affects about 26 million Americans. It strikes people of all races, but African Americans are at greater risk, mostly because they have higher rates of diabetes and high blood pressure, the two leading causes of kidney disease.

Kidney disease often strikes without warning. It can be prevented or delayed, but if left untreated it can lead to kidney failure or even death.

In the new study, NIH scientists and their colleagues examined 759 African Americans who had kidney disease due to high blood pressure. The researchers assessed the patients’ health for at least 9 years. All the patients took blood pressure medications and tried to keep their blood pressure low.

During the study, about one-third of the patients had a slow weakening of kidney function, similar to the decline seen as healthy people age. But in about one-fourth of participants, kidney disease got substantially worse, even with very good blood pressure control and use of medications.

These findings highlight the importance of early detection and treatment of kidney disease. Talk to your health care provider about your risk for kidney disease and how you can keep your kidneys healthy.

“Despite these sobering results, blood pressure control is still vital in kidney disease and in many other diseases,” said NIH Director Dr. Elias Zerhouni.