I have already mentioned the Hunger Hormones Leptin and Ghrelin in so many articles but I never really explained the science behind it. As you seem to like scientific articles, I figured I should go more into detail on this topic.
In fact, knowing why you get hungry is very useful. I already taught you how to decrease food cravings. Now, you are going to learn how to understand you body’s signals even better.
Difference between Appetite and Hunger
First of all, appetite and hunger are often used interchangeable, yet they are not the same thing.
Appetite is the “desire” to eat something. You could also call it “food cravings”. If you have read my articles on cravings, you know that the Reward System in the Brain plays a major role here.
Food provides the body with nutrients needed to keep you going throughout the day. Thus, appetite and cravings are good things. It is only when we lose control and “live to eat” when health problems like weight gain occur. Many times your cravings and appetite depend on the balance of hormones in the brain and body, particularly endorphins and dopamine.
However, hunger is the uncomfortable feeling caused my an empty stomach. After a few hours of not eating, hunger pangs occur. This is a sensation involving contractions of the empty stomach and the discomfort you feel in your abdominal region.
To visualize this, think of your last big meal. Mine was lunch and I had a workout before. Thus, I experienced severe contractions in my stomach and had the feeling of discomfort in my belly. My mouth was dry and all I wanted to do is eat. I was hungry.
Now, after my meal (which was quite big), I still had the feeling like I needed something sweet. I was not hungry anymore, but my appetite was not gone. Call it chocolate cravings. Apparently, the nutrients in my meal were not sufficient to restore the balance of endorphins on my brain. After I had a small piece of dark chocolate, my appetite was gone and I felt satiated.
Hunger Hormones: Leptin and Ghrelin
Hormones regulate every single process in our body. Think of them as emergency responders of the body, constantly on an alert to be released or depressed in order to maintain homeostasis. Digestion itself involves many more hormones than solely Ghrelin and Leptin. Still, to understand the physiology of hunger, it is crucial to learn more about Ghrelin and Leptin first.
Leptin is synthesized in our fat cells. It is secreted mainly by white adipose tissue and its levels correlate with the amount of body fat. Also, Leptin is released in a pulsatile fashion, with higher levels in the evening and early morning hours. Leptin levels in our body reflect the amount of energy stored in fat and acute changes in caloric intake.
Increased Leptin signals our brain that we have enough energy stored, so there is no need to eat. Thus, it is also called the “hunger depressing” hormone. It also surpresses appetite. Whenever you eat a meal, Leptin levels increase.
In our brain, there are receptors made specifically to bind Leptin. Once Leptin is linked to its receptor, several signal transduction pathways, which are important for regulating energy homeostasis, food intake and glucose homeostasis, are activated. These receptors are found mainly in the hypothalamus, the major region of the brain for regulation of energy homeostasis and endocrine functions.
Leptin directs the central nervous system to adjust food intake and energy expenditure accordingly. In our hypothalamus, there are neural networks that can be divided in two groups. They release neurotransmitters that either have an appetite-diminishing (anorexigenic) or appetite-stimulating (orexigenic) effect.
Leptin also interacts with the Reward System in our brain, the mesolimbic dopamine system, which is responsible for motivation and reward for feeding.
In fact, studies on mice have shown that Leptin might not only decrease food intake but also signal the body to increase energy expenditure, by activating sympathetic nerve activity and thermogenesis in brown adipose tissue.
⇒ What happens when you fast
It has been confirmed in studies on mice and human that fasting decreases leptin levels drastically. As a result, neuroendocrine system to regulate acute energy deprivation are triggered. This includes a decrease in reproductive hormone levels, thyroid hormone levels, which slows down metabolism. Also, human-growth-factor hormones are increased to utilize more of our body’s energy stores.
According to new studies, hypoleptinemia might be the associated with anorexia nervosa, exercise-induced amenorrhea and trouble getting pregnant. Also, researchers discuss that extended periods of low leptin levels might enhance development of anovulation and osteoporosis.
⇒ To sum it up
Leptin levels reflect the amount of energy stores in adipose tissue and direct the central nervous system in regulating energy homeostasis, neuroendocrine function and metabolism.
Leptin deficiency results in neuroendocrine deficits, including infertility, as well as metabolic abnormalities.
This is the exact opposite of Leptin. Ghrelin is secreted primarily in the stomach and secondarily in the small intestines and colon. It may also be expressed in pancreatic islets, hypothalamus , pituitary, and other tissues in the periphery.
Ghrelin has an important role in the short-term regulation of appetite and the long-term regulation of energy balance and glucose homeostasis.
Ghrelin is orexigenic; it is released and circulates in the blood stream under fasting conditions, indicating that it signals the body that it lacks nutrients. It communicates with the brain and leads to the release of other hormones from the hypothalamus, among them Neuropeptide Y. Thus, we experience hunger.
As a matter of fact, recent studies implicate ghrelin in the pathogenesis of many diseases, including obesity, Prader–Willi syndrome, cachexia, Anorexia nervosa, cardiovascular diseases, reproductive disorders, diabetes and inflammatory bowel disease.
Let’s end this article here for today, as it already contains a lot of information. I think it is best to split these more medical/scientific articles, as you will have more time to “digest” and fully understand the physiologic processes. At least it took a while for me to distinguish between the different hormones when I learned this in med school!
If you liked this article, leave me a comment and spread the knowledge!
Wish you all a wonderful day,