Body Fat Set Point Theory 

The Body Fat Set Point theory says that your body works to maintain a fixed body fat percentage. When you lose weight, or gain it in small quantities, your body will work to return to that pre-set fat percentage.

The set point is controlled by the size of our individual fat cells, also known as adipose cells. Adipose cells secrete hormone signals that go to the brain and control various metabolic functions. These fat cells control leptin, an important hormone that decreases hunger and increases metabolism– critical for aiding in weight loss. As you lose weight, your adipose fat cells decrease in size and produce less leptin, leading to increased hunger and decreased metabolism. The more you lose weight and decrease the size of your fat cells, the more your hormones begin to work against you to defend your set point.

Think of the body fat set point as a thermostat, like the one that controls your home’s heating system. If you have the thermostat set to 72 degrees but the temperature in your home falls to 70, then the heater kicks on and brings the temperature back up to 72, at which point the heater turns off. The body does the same thing when you lose weight. If you fall too far below your set point, then hunger hormones will increase, metabolism will decrease, and your body will fight to get you back to your original weight. If your weight set point is 200 pounds, when you start dieting and losing weight, and you get far enough below your set point (say 190 pounds), your body increases your hunger hormones and decreases your metabolism to get you back.

Weight loss medications and weight loss surgeries can help decrease this set point. Let’s look at a common weight loss medication, Wegovy, aka Semaglutide. Wegovy helps patients overcome increased hunger hormones when leptin falls as they lose weight; as leptin continues to decrease at each new set point, we increase the dosage to help you reach your next goal.

For example, if you start Wegovy at 0.25mg weekly, then you might decrease your set point from 200 to 190 pounds. Once your weight reaches 180, your hunger hormones really kick in, so we increase the medication to 0.5mg. Your new set point may be 180 pounds, so once you hit 170, your hunger hormones ramp up again, so we increase to 1.0mg to decrease your set point again. This process continues until we reach the maximum dose of the medication. At this point, we would need to stay at that same weight and dose of the medication to keep the weight off, or we could add another medication or surgery to decrease the set point further.

It’s important to note that obesity is a chronic disease, just like hypertension or diabetes, so medications are usually needed long-term to control your hunger hormones. Patients who stop medications typically experience increased hunger and return to their original set point. Some people can overcome this, but most cannot. Once a patient has reached a healthy weight, we usually start decreasing the medication slowly, but if they start gaining back weight, we increase the medication(s) back to the dose that worked for them.

It is critical to create a long-term plan after losing significant weight. When weight is regained quickly, patients risk increasing their original set point. Instead of fat cells returning to their original size and decreasing hunger hormones, patients who re-gain quickly increase the number of smaller-sized fat cells, which triggers greater hunger and lower metabolism.

Animal studies showed that feeding rats a calorie-restricted diet decreased the size of their fat cells but not the number. Later, when researchers let the rats eat whatever they wanted, they only gained back some weight but did it quickly. Instead of the fat cells returning to their original, larger size, they stayed about the same, yet the number of cells increased by about 50%. This is called pre-adipocyte differentiation. This typically happens with massive overeating, such as binge eating after losing a lot of weight. More fat cells mean greater potential for fat storage. 

The combined reduction in fat cell size and increase in quantity led to a decrease in their original, pre-weight-loss leptin levels, and the rats did not stop regaining weight until they gained above their original set point. They stopped gaining weight when their fat cells returned to their original size but now with more total cells. The rats reprogrammed their set point to a higher number which the body will continue to defend.

Body fat set points present a significant challenge to those with obesity or excess weight. Understanding how hormones and fat cells affect your weight can help you and your doctor create a successful long term weight-loss plan. For more information about weight loss and body fat set point, check out the resources below or see my website:

Resources: Diets, Apps, Exercises, Medications, Videos

 

YouTube: Dieting is Making You Fatter? – Body Fat Set Point Change Theory by Layne Norton, PhD

 

Animal Study
Jackman, M. R., Steig, A., Higgins, J. A., Johnson, G. C., Fleming-Elder, B. K., Bessesen, D. H., & MacLean, P. S. (2008). Weight regain after sustained weight reduction is accompanied by suppressed oxidation of dietary fat and adipocyte hyperplasia. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 294(4), R1117-R1129.

Seth Jarrell, MD