Precision Nutrition GI Hormones and Neurotransmitters

Motilin

A gastric hormone that activates duodenal/ jejunal receptors to initiate peristalis/ Released when bicarbonate is dumped into the small intestine and between meals/when fasting Secreted by cells in small intestine Promotes muscle contraction of GI tract, and when released between meals, you'll notice borborygmus

Leptin

A hormone produced by adipose (fat) cells that acts as a satiety factor in regulating appetite./ Released with low calorie intake and low body fat levels Secreted by fat cells Low leptin means a slower metabolism and drive to increase food consumption. Administering leptin analogs in humans is ineffective for appetite suppression. Leptin exists to prevent starvation, not to lose weight. Only when leptin is provided along with amylin, slight fat loss may occur

Cholecystokinin (CCK)

A hormone secreted by the samll intestine (duodenum) in response to the presence of fats. It promotes release of bile from the gallbladder and pancreatic juice from the pancreas,and reduces stomach motility./ Released when protein and fat enter the small intestine Secreted by cells in small intestine Signals pancreas to produce enzymes, inhibits gastrin, stimulates gallbladder contraction, and triggers satiety in the brain

Secretin

A hormone secreted by the small intestine (duodenum) in response to low pH (e.g., from stomach acid). It promotes the release of bicarbonate from the pancreas to act as a buffer./ Released when acids reach small intestine Secreted by cells in small intestine Produces pancreatic fluid, inhibits gastrin release, and enhances effects of cholescystokinin

Norepinephrine

A precursor of epinephrine that is secreted by the adrenal medulla and also released at synapses; Decreases digestive activity, which makes sense during fight or flight situations. When immediate, decisive, or aggressive action is required, digestion is a low priority. Stress not requiring immediate fight or flight type responses (such as deadlines, relationship challenges, etc.) also provokes norepinephrine release and this can impair digestive function

Neurotensin

As dietary fat reaches the last section of the small intestine, cells located in the intestinal walls release neurotensin. It relaxes the lower esophageal sphincter, blocking the release of stomach acid and pepsin to regulate GI contractions; Peptide-neuro modulator neurotransmitter that decrease levels in spinal fluid of patients with schizophrenia

Acetylcholine

Common vertebrate neurotransmitter, especially in neuromuscular junctions; In the digestive system, this neurotransmitter is responsible for stimulating digestive activity. It acts to stimulate smooth muscle contractions in the digestive organs and help move food through the GI tract. It also stimulates the release of other digestive hormones, dilates blood vessels, and increases intestinal secretions. It runs counter to the actions of norepinephrine

Gastrin

Digestive hormone that stimulates sustained secretion of gastric juice from the stomach/ Released when food enters stomach, protein dense foods are the most potent stimulator of gastrin Secreted by cells in stomach/small intestine Initiates the digestion process

Nitric oxide and Substance P

Found in the brain and enteric circulation, these compounds are associated with vasodilation in the gut, assisting in more blood flow for nutrient delivery/uptake

Calcitonin (CT)

Inhibits the breakdown of bone; causes a decrease in blood calcium concentration/ Released in response to gastrin and serum calcium levels; secreted by cells in the thyroid, GI tract, and pancreas; complementary signal responsible for fine tuning the eating process

Gamma-aminobutyric acid (GABA)

Neurotransmitter that reduces activity across the synaptic cleft and thus inhibits a range of behaviors and emotions, especially generalized anxiety; GABA can act as an excitatory or inhibitory neurotransmitter depending on which cell receptor it binds to. The chief role of GABA is to stimulate GI motility and contribute to GI wall mucosal function; a neurotransmitter whose low activity has been linked to generalized anxiety disorder; a widely distributed amino acid transmitter, and the main inhibitory transmitter in the mammalian nervous system

Somatostatin

Released between meals to reduce digestive activity Secreted by stomach, intestine and pancreas Slows gastric emptying, reduces GI muscle contractions and blood flow to gut

Serotonin

Released both in the brain and the enteric nervous system. In the brain, serotonin is linked to modulating anger, aggression, temperature, mood, sleep, appetite, and vomiting. Following meals, serotonin concentrations reach a maximum within 1-2 hours.In the gut, serotonin is produced by cells located in the small intestine. In this capacity, serotonin increases small intestinal motility, reduces stomach acid production, and, in high amounts, can cause nausea. This is why anti-depressant drugs like Prozac can sometimes lead to diarrhea and nausea. These drugs make more serotonin available not only in the brain (where they exert their anti-depressant effect), but the gut, where they can cause serotonin excess

Ghrelin

Released in response to low food intake/fasting Secreted by cells of the stomach, pancreas, placenta, kidney, pituitary and hypothalamus Stimulates release of growth hormone to encourage eating and acts to regulate energy balance long-term

GLP-1

Released when blood glucose levels are above the norm Secreted by cells of the gut in proportion to the amount of energy ingested Stimulates insulin and amylin secretion, may assist in signaling the brain to stop eating

Gastric Inhibitory Polypeptide (GIP)

Released when food enters small intestine Secreted by cells in small intestine Enhances insulin release, inhibits gastric secretions and motility

Enteric Nervous System

The nervous system of the gastrointestinal tract. It controls secretion and motility within the Gi tract, and is linked to the central nervous system; an extensive meshlike system of neurons that governs the functioning of the gut

Endocannabinoids

These participate in glucose and insulin metabolism in muscle and fat tissues. When endocannabinoid receptors are blocked, insulin sensitivity is improved. This can lead to less food intake and fat mass. When food intake is decreased, there seems to be an upregulation of endocannabinoid receptors and serious hunger is soon to follow (think: smoking weed and making a Taco Bell run). It seems that a diet with lots of omega-6 fats can promote endocannabinoid production, while a diet higher in omega-3 fat can inhibit it. Researchers are trying to develop endocannabinoid receptor blockers for humans; Lipid-derived messengers sometimes referred to as the brain's marijuana. These messengers control the release of neurotransmitters, usually by inhibiting them, and can affect the immune system and other cellular parameters. Endocannabinoids also play an important role in the control of behaviors

Neuropeptide Y (NPY)

This neurotransmitter is present in both the brain and the enteric nervous system. In the brain, its action is to stimulate hunger and food intake while discouraging physical activity. Working in conjunction with leptin and corticotropic releasing hormone, this neurotransmitter plays a role in metabolism and body composition. It's typically released when body fat is low or food is scarce. In the gut, Neuropeptide Y generally slows gastric emptying and transit time; neurotransmitter found in several brain areas, most notably the hypothalamus, that stimulates eating behavior and reduces metabolism, promoting positive energy balance and weight gain; peptide that blocks the satiety actions of the paraventricular nucleus

PYY 3-36

a peptide hormone, secreted by the intestines, that probably acts on hypothalamic appetite control mechanisms to suppress appetite/ Released in the hours following a meal, presumably to suppress appetite; Secreted by the small/large intestine Inhibits stomach motility while increasing water and electrolyte absorption in the colon. May also suppress pancreatic enzyme secretion. Obesity seems to be a PYY 3-36 deficient state

Vasoactive Intestinal Peptide (VIP)

duodenal hormone that stimulates buffer secretion, inhibits acid production, and dilates intestinal capillaries; VIP is important to the digestive process through its ability to inhibit the release of gastrin, inhibit the secretion of acid, stimulate bicarbonate secretion from the pancreas, induce smooth muscle relaxation and vasodilation, stimulate pepsinogen release, and stimulate the secretion of water and electrolytes into the small intestine. Most of these functions are responsible for slowing down stomach activity while stimulating intestinal activity

Amylin

secreted by pancreatic beta cells in response to food intake & elevated blood glucose concentrations; slows gastric emptying & suppresses glucagon secretion & modulates appetite/ A partner hormone to insulin, released after meals; Secreted by the pancreas It slows the emptying of our stomach and suppresses glucagon (glucagon raises blood sugar)