Dr. David L. Katz
Photo: Mackenzie Stroh
Q: Is it true that I'm stuck with the fat cells I have? Or is there some way I can lose them?
— Anonymous

A: No, you're not stuck: You can shed fat cells, but you won't find it to be a stroll in the park. When we gain weight as adults, we are mostly enlarging the fat cells we have instead of adding more. This process has a medical name: hypertrophic obesity.

Reversing this type of weight gain requires shrinking the cells, but they don't put up a huge fight when being shrunk from plus size back to normal. While not exactly easy, this type of weight loss is more doable than reversing the other kind of obesity: hyperplastic.

When we quickly put on a lot of pounds in early childhood, at puberty, and sometimes even as adults, we can grow new fat cells. Known as hyperplastic obesity, it poses a daunting challenge. The only way to be thin if you have an excessive population of fat cells is to shrink them below normal size, which is where things get really tough. The cells begin to produce less leptin, a hormone that signals the brain when you're full. You'll end up feeling ravenous all the time. If you find the will to lose more than 10 percent of your body weight (more than 20 pounds for someone who weighs 200), eventually you'll induce a process called apoptosis—cell death. You could begin trimming your population of fat cells. Once you do, you'll find that maintaining a lower weight gets easier.