What Do Fat Cells Do

By Nanci Hellmich, USA TODAY

PHOENIX — Most people think of fat as an inert blob, but fat cells release powerful chemicals.

In obese people, the fat tissue often produces too many bad hormones and too few good ones, says Susan Fried, director of the Clinical Nutrition Research Unit of Maryland at the University of Maryland School of Medicine in Baltimore.

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Fried and other scientists discussed the latest research on fat cells here at the annual meeting of the Obesity Society. Fried talks about the relationship between obesity and fat cells.

Q: Do people have different numbers of fat cells?
A: A person at a healthy weight might have 10 billion to 20 billion, and an obese person can have up to 100 billion. Babies are born with about 10 billion. You naturally increase the number of fat cells, like other kinds of cells, as you grow.

Q: Is everybody born with the same number of fat cells?
A: No. There is a genetic component to how many you have, but I would say less than 5% of obese people have a genetic tendency to have a greatly excess number. It appears in animal experiments that animals that are overnourished in the womb and shortly thereafter tend to have more fat cells.

The number can increase at any time if you overeat long enough and hard enough. When your fat cells get to a maximum size, they send a signal to (fat-precursor) cells to become full-fledged fat cells. It may be that having too many hungry fat cells somehow makes us eat more.

But overweight people (those who are not obese but are one to 30 pounds over a healthy weight) don’t generally have an excess number. You can gain 30 pounds easily by increasing the size of current fat cells and not adding new ones.

Q: What do white fat cells do?
A: White fat cells store energy and produce hormones that are secreted into the blood. In theory, if we overeat, our fat cells will produce a little more of the hormone leptin, which will go to our brain and tell us we have plenty of energy down here; not to eat any more. If it worked perfectly, no one would get fat, but it doesn’t work perfectly, so many of us do get fat.

When fat cells are small, they produce high amounts of some hormones such as adiponectin. It is a good guy because it keeps the liver and muscles very sensitive to insulin and fights diabetes, heart disease and other diseases. But in obese people, fat cells tend to shut down the production of adiponectin, and that has bad effects on health, and it’s one reason people develop diabetes and heart disease.

Q: Does losing weight shrink the size of your fat cells?
A: If you are eating less energy than you require, your cells release fat for fuel and then shrink. If you are obese and have 100 billion fat cells and you lose a lot of weight, your fat cells may go down to a normal size, but you still have 100 billion. So you may still be overly fat, but you will be healthier since small fat cells produce more of the good fat hormones like adiponectin.

Q: Can you explain the new discoveries about brown fat?
A: While a white fat cell stores energy, a brown fat cell’s job is basically to generate heat. We always thought brown fat was only in human babies and helped keep them warm. Now there is more evidence that there are more brown fat cells in adults than we originally thought. Brown and white are not really related because they don’t come from the same precursor cell or stem cell.

Brown fat cell comes from the same kind of precursor cell as a muscle cell. Even though there are very few brown fat cells in adult humans, it looks like there is a lot of variability between people. There is increasing evidence that some humans, particularly lean ones, tend to have brown fat cells mixed in with their white fat cells in some regions of their body. So if we can figure out how to persuade the body to make more brown fat cells, we may be able to fight the tendency to gain excess weight.