In the last article I addressed the Hunger Hormones Leptin and Ghrelin. If you haven’t read that one yet, make sure to do so, as this article is the follow-up.
Let’s talk about the many other gut hormones regulated by the central nervous system today.
The nervous system and Hunger
Neurons in the hypothalamus communicate with cells on other parts of the brain to regulate the release of hormones.
When we eat a meal, the break-down products of food – amino acids, fatty acids and glucose – regulate hormones such as Insulin.
To evaluate the contents of the gut, the brain uses information from vagal nerve fibers. In fact, the vagal nerve is a cranial nerve but you can find nerve fibers all around our stomach, pancreas and liver (as you can see in the picture above ). This nerve carries signals between the brain and gastrointestinal tract. As a result, the brain can sense a difference between macronutrients.
As our stomach is filled with food, the muscles in our gut are stretched. This is another signal that the vagal nerve fibers carry to the brain and result in inhibition of the hunger center in the hypothalamus.
In addition to that, blood levels of fatty acids, amino acids and glucose provide a constant flow of information to the brain, regulate energy intake and hunger.
Sight, smell and memory of food
I will go into much more detail on how the mere sight or smell of food increases hunger and cravings in following posts. For now, you should know that the cranial nerve nuclei that get information from our visual and olfactory nerves are directly linked to the vagal nerve nuclei.
In addition to that, memory cells in our Reward system (mesolimbic pathways) in the brain that have saved information on pleasant food are activated. Thus, you experience cravings and sensations like mouthwatering and even contraction in your stomach.
During food absorption, a number of hormones are released from the stomach itself. Among these are Insulin and cholezystokinin (CKK). These hormones play a major role in the digestion of carbohydrates and fats. Also, CKK depresses the release of Neuropeptide Y, Ghrelin and Glucagon, which are all hunger increasing hormones.
Many gut peptides have been shown to influence energy intake.
The most well studied in this regard are cholecystokinin (CCK), pancreatic polypeptide, peptide YY, glucagon-like peptide-1 (GLP-1) and ghrelin. With the exception of ghrelin, these hormones act to increase satiety and decrease food intake. These gut hormones also have a direct effect on the hypothalamic centres of appetite control.
Lastly, there is one more gut hormone that regulates the release of most other (gut) hormones: Somatostatin, also called SRIF.
It inhibits release of hormones such as gastrin, secretin (important hormones to regulate gastric acid production) and CCK. Also, it inhibits gastric acid production, prolongs gastric emptying, reduces intestinal motility and decreases splanchnic blood flow, and lastly decreases blood levels of Insulin, Glucagon and pancreatic enzymes.
To sum it up
Hormones increasing Hunger are:
- Orexin: released in the Hypothalamus
- Ghrelin: released in the Stomach
- Insulin: released in the pancreas
- Glucagon: released in the pancreas
Hormones decreasing Hunger are:
- Leptin: Released and synthesized in fat cells
- Gut peptides, such as PYY (another Neuropeptid) and CKK: Released in the digestive tract
Other factor regulating the release of hormones are:
- Vagal fibers around the digestive tract
- Stretched muscle fibers in the digestive tract
- Smell, sight and memory of food and its taste (strong association with the mesolimbic pathway)
I hope you enjoyed this little series on Hunger Hormones.
In the next articles, I will cover some diseases linked to these hormones and provide tips on healing and prevent them with proper nutrition and exercise. Following the principle of Fitness and Food as Medicine!
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