How do fat cells work?

What are fat cells?
Picture a little Ziploc bag filled with a blob of fat (triglyceride) floating in some fluid...that’s basically what one fat cell looks like. But fat cells, or adipocytes, are more than inanimate bags of fat. Your fat cells are alive; they release proteins and hormones and communicate with other parts of your body.

How do I find my body fat percentage?
The National Institutes of Health (NIH) recommends using Body Mass Index (BMI; a ratio of your height and weight) to estimate your body fat. While BMI may be a practical metric for a population, as an individual, you can do better. BMI is a misleading indicator of body fat for almost 1 in 5 people, particularly athletes. More accurate methods include digital scales that measure weight and body fat, as well as body fat calipers.

What’s the right amount of body fat?
Everyone needs a certain amount of essential body fat for survival: approximately 3 percent of body weight for men and 12 percent for women (due to “sex-specific” fat necessary for reproductive functioning). Too much stored body fat (especially “visceral fat” around your abdominal organs), however, is associated with negative health outcomes, including heart disease and diabetes. If you want to lose weight, you want to lose storage body fat. What’s a healthy body fat percentage for you? Start here.

Is there more than one kind of fat cell?
Yes. We know there are at least two: brown and white. White fat cells are the biggest problem for people who want to lose weight. A fat cell can start off storing a little blob of fat, but you can stuff the Ziploc so that it holds four times the original amount of fat. After that, if you still need more storage for “leftover” fat, you’re going to need a new Ziploc, which brings us to our next question…

Does the body make new fat cells?
Yes, your body creates new little Ziplocs when necessary (lean muscle doesn’t “turn into” body fat). This seems particularly true for fat cells in the thighs. If you have excess “energy” to store, and your thigh Ziplocs are already full, your body will create new fat cells for your thighs, a phenomenon that has been observed in both men and women. An eight-week study found that, on average, 3 pounds of lower-body weight gain was associated with the generation of 2.6 billion new fat cells. This is why, if you carry excess weight around your hips and thighs (the “pear” shape), it’s often the most difficult place to lose weight.

If I lose weight, do I lose the fat cells I have?
Alas, no. Here’s the rub: once those little Ziplocs are yours, they’re yours to keep, till death do you part. You can definitely deplete the fat cells you have so that they shrink in size, but that’s not so easy either. When your Ziplocs get too empty, they produce less leptin, a hormone that helps trigger the sensation of fullness… so you feel hungrier, longer. Additionally, recent research has found that fat cells release a protein, sLR11, which appears to “fight” to preserve, or “lock down,” your body fat. In other words, your fat cells are each working to hold on to their fat stores.

The one exception to the “fat cells are forever” rule? Liposuction. Liposuction literally sucks the fat cells out of your body. But, over time, people commonly regain body fat post-liposuction, even if it’s in different areas of the body.

Is the weight I lose from diet and exercise body fat?
In addition to losing body fat, you also lose some lean body mass. The best way to maximize the percentage of weight lost from body fat is through exercise, including building muscle.  Keep in mind though, even contestants on the television show, The Biggest Loser, who were on an extremely vigorous exercise regimen, lost an average of 128 pounds, but only 82% of that weight was body fat.

How do I minimize excess body fat?

  • Eat smart. That includes minimizing processed foods and artificial sweeteners, but does not include eliminating dietary fat. Fat doesn’t make you fat.
  • Protect your sleep. Insufficient sleep is associated with weight gain.
  • Actively manage stress and anxiety. Excess levels of hormones associated with stress, like cortisol, stimulate appetite and promote weight gain.
  • Weigh yourself regularly. Weight gain can be insidious. Stepping on the scale regularly allows you to “right the ship” before the pounds pile on. (Note: this advice may not be right for you if you have had an eating disorder.)
  • Move! Make exercise a part of your daily routine, whether that’s doing TRX at the gym, taking the stairs at work, or doing T‘ai Chi in your wheelchair.

Clichés such as “Eat less, exercise more” and “Everything in moderation” are simplistic at best, and patronizing at worst, for those struggling to overcome obesity. While a minority of those with obesity do achieve and maintain significant, long-term weight loss, the body’s physiological adaptations to weight loss serve to make long-term weight loss very difficult. The “formerly-obese” will always have billions more fat cells than the “never-obese.” Ultimately, the science of fat cells serves to highlight an inconvenient but important truth: the best weight management strategy is prevention.

Stacey C. Cahn, PhD is associate professor of clinical psychology at the Philadelphia College of Osteopathic Medicine (PCOM). Dr. Cahn specializes in obesity, weight stigma, eating disorders, and cognitive-behavioral therapy. 

Christopher S. Adams, PhD is professor of anatomy at the Philadelphia College of Osteopathic Medicine (PCOM). Dr. Adams conducts research on the prevention of orthopaedic implant infection.


Read more Goal Getter for healthy eating, weight loss and more.