The Biology of Fat Cells

CURE, Fall 2005, Volume 4, Issue 3

Not all fat is alike and not all fat is bad for you. Two types of fat cells, white and brown, differ dramatically from each other. When a person talks about fat in regards to weight gain, white fat cells are the culprit. But brown fat cells burn energy rather than store it. Research into both cell types will determine if humans can use fat cells to lose weight and stay healthy.

White Fat Cells

White fat cells store triglycerides when people eat and later release fatty acids when people fast to provide energy. The more fat stored, the bigger the cells grow, up to six times their normal size. When a white fat cell reaches capacity, it begins to multiply. When the body loses fat, the size of the cells decrease, but typically, the total number of fat cells remains the same.

What seems to be nothing more than a glistening glob of fat, a mature white fat cell, or adipose tissue, is actually a bustling factory that produces over 100 hormones, proteins and other chemical factors to help perpetuate the body’s fat stores. What was once thought of as just fat now makes up its own endocrine organ. Research into whether the many secreted factors from fat cells can be regulated may provide a way to maintain or lose weight and possibly avoid the health risks that come with obesity. However, given the complexity of these cells, modulating one factor will not likely solve the problem of obesity.

Brown Fat Cells

When you’re born, you have brown fat cells in addition to adipose tissue. Filled with energy-generating mitochondria, brown fat cells are present in newborns, but humans tend to lose these “good” fat cells with age.

Laboratory research into brown fat cells could uncover potential treatments for obesity. One area of research hopes to utilize mesenchymal stem cells, which are found inside white and brown fat. By understanding how a mesenchymal stem cell decides which type of fat cell to become, scientists can potentially guide the cell to become an energy-producing brown fat cell.

A protein found in brown fat cells’ mitochondria may also prove useful. Increasing this protein will not likely work in humans because of an absence of brown fat cells, but scientists have found a gene in humans that codes for a similar protein that may produce the same effect.

“We may be able to tap into brown fat and make it work harder with drugs, but as a species we just don’t have a lot of brown fat,” says Caroline M. Apovian, MD. “We haven’t been able to make the little amount of brown fat work for us yet.”