We have discussed many different aspects of hormones on this blog, and the reader is most likely aware that hormones function as signaling molecules. They are secreted from one part of the body, travel through the bloodstream, and arrive at a target tissue to transmit the message. Most of our discussions have focused on the sex & adrenal hormones, such as: estrogens (estradiol, estriol), progesterone, testosterone, DHEA, and cortisol. These hormones are vitally important to cellular metabolism, anabolism, and catabolism. However, our discussion today will focus on some lesser known hormones.
There are two main antagonistic hormones that drive our hunger/satiation response. They are leptin and ghrelin. Leptin is produced in adipose (fat) cells and serves to decrease appetite. If you think about it biologically, this is intuitive and easy to remember. As fat increases, the body signals (via the hormone leptin), that the energy stored as fat is sufficient and that we should eat less. Thus, leptin signals our brain to eat less. Now, you may be thinking to yourself, “if the hormone that tells us to eat less is produced in fat cells, wouldn’t obese individuals have lower appetites?” In a perfect world, you would be correct! But science has discovered that as we gain weight, we become desensitized to the effects of leptin. This means that the suppressive effect on appetite is blunted over time. This phenomenon is very similar to what happens in patients with diabetes – the body becomes resistant to the effect of insulin, the hormone that lowers blood sugar.
Ghrelin can be thought of as the opposite of leptin. It is produced in the gastrointestinal tract and tells the brain that energy stores are low and need to be replenished. The brain responds by making your appetite increase, mouth water, and stomach acid begin to increase in preparation for food intake. Ghrelin is secreted when the stomach is empty. When the stomach is stretched and full, ghrelin secretion stops. This mechanism makes sense biologically when we think about it.
If you are concerned about your weight or appetite, keep the biologic function of these hormones in mind, and use them as motivation to institute diet and lifestyle changes. As I always tell my patients, be wary of “lose-weight-quick” schemes. The healthiest, most natural, and easiest way to lose weight is to begin making small substitutions in your diet and get active. Even something as simple as a walk around your neighborhood after dinner, or 30 minutes on an inclined treadmill while you watch TV or favorite streaming service on your cell phone will, over time, pay off dividends.