Our brain is the command and control centre, with sight, hearing, smell, taste, and touch as five external sensory inputs and vestibular sense (sensors of balance are in the inner ears), proprioception (sensors of body position and movement are in muscles and joints), and interoception (pain and other sensors of internal state of the body are widely distributed) as three internal sensory inputs. The body is controlled directly through the electric impulses of the nervous system and remotely through chemical messengers released by the endocrine system.
The heart is the logistics hub, and blood vessels and lymphatics are the transport pathways, lungs are the oxygen plant, kidneys and urinary tract are the waste disposal facility, the immune system is the external defence and internal security, skeletal system is the structural support, physical protection, and mobility enabler, and skin is the external barrier. The reproductive system is essential for the survival of the species, but non-essential for the individual’s survival. Then who is the most impactful influencer of our health?
GUT THE SUPER IMPACTFUL INFLUENCER: It is becoming increasingly obvious that our most underrated organ, the gut (gastrointestinal tract or GIT) is not just a port of entry and exit; it is the most influential digestive, endocrine and immunity organ in the body and has the liver as the chemical industry, detoxifier, nutrient store, bile producer and defender, and pancreas as the only exocrine (secretes digestive juices into a duct) and endocrine organ (secretes Insulin and other hormones into the blood). The stomach is the acidic food receptacle, steriliser, and digester, and the intestines are the alkaline digesters, absorbers of nutrients, and a waste disposal channel. The gall bladder is the bile flush tank.
The appendix acts as a “safe house” for beneficial gut bacteria, allowing them to repopulate the gut after illness or diarrhoea. The gut and its colonies of beneficial microorganisms significantly influence and impact our health by modulating fat metabolism, glucose consumption and storage, and inflammation. Gut malfunction is not just indigestion, acidity, ulcers, gallstones, or inflammation; it leads to diabetes, non-alcoholic fatty liver disease, obesity and related metabolic disorders, and to the autoimmune disorders Celiac disease (triggered by gluten), and Inflammatory Bowel Disease (IBD), which includes Crohn’s disease and ulcerative colitis.
The gutbrain axis is a bidirectional communication network between the gut and brain involving neural, endocrine, and immune pathways, and affects mood, cognition, neuroinflammation, and overall health of the brain. GUT AN UNDERESTIMATED ENDOCRINE SUPERPOWER: With more than 30 hormones and a multitude of bioactive peptides, the gut is the largest, most complex, and multifaceted endocrine organ in the body. Gut hormones play a crucial role in regulating appetite, satiety, glucose homeostasis, and other metabolic processes. The pancreas secretes Insulin that helps store or burn glucose, Glucagon that helps release stored glucose, and many other hormones.
Problems with Insulin or Glucagon can cause diabetes. The intestines produce hormones like Secretin, the first hormone to be discovered, leading to the discovery of the endocrine system. It stimulates the production and release of digestive juices, bile, and neutralization of acid from the stomach. The intestines also release Gastrin that stimulates digestive enzyme pepsin, and acid in the stomach, which is crucial for digestion, nutrient absorption, and immune protection. Cholecystokinin releases bile and digestive enzymes.
RECENTLY DISCOVERED OBESITY RELATED GUT HORMONES AND DRUGS: Recently discovered gut hormones are Gastric inhibitory polypeptide (GIP) for insulin secretion in 1970, GLP-1 (Glucagon-like peptide-1) that stimulates insulin secretion in 1986, Ghrelin, the “hunger hormone” in 1999, and LEAP2 (Liver-Expressed Antimicrobial Peptide2) that counteracts ghrelin’s effects in 2003, and many more. The discovery of these hormones and Leptin the “satiety hormone” (produced by fat cells) discovered in 1994 were a result of research related to sedentary lifestyle and junk food caused obesitymetabolic syndrome (heart disease, stroke, and type 2 diabetes) crisis, and consequences of bariatric surgery (reduces stomach capacity, food absorption and Ghrelin levels).
The further search for compounds that may induce satiety similar to the actions of hormones Leptin, CCK, insulin, and GLP-1, etc., and control blood glucose levels, led to the development of many drugs for weight loss and diabetes. These drugs have been approved for longterm weight management in adults: fat absorption blocking drug orlistat, satiety inducing drug combinations phentermine-topiramate, and naltrexone-bupropion, and GLP-1 mimicking antidiabetic drugs liraglutide, tirzepatide, and semaglutide (Wegovy, Ozempic). LEAP2 is being explored as a potential target for treating obesity and related metabolic diseases.
GUT IS A SUPER-EFFICIENT IMMUNE BARRIER AGAINST INGESTED PATHOGENS: Just like anti-trespass security devices are at entry points, our main defence barriers are at potential ports of entry, the skin (through wounds and bites), eyes, ears, nose and respiratory tract (by air borne pathogens like Chickenpox, flu, whooping cough, Covid, etc.), mouth and gut (by water and food borne infections like diarrheal diseases, food poisoning, H.pylori stomach infection, typhoid, cholera, listeriosis, hepatitis, parasitic infestation) and genitourinary tract (by urinary, genital tract and sexually transmitted infections). When these barriers fail, or are penetrated as in a wound, ulcer, needle prick, etc., the systemic immune system deals with the pathogen. While bacteria are present on various surfaces of the body, including the skin and respiratory tract, the sheer volume and diversity (over 1,000 types) of bacteria within the gut far surpass those found elsewhere.
This vast community of bacteria, fungi, and other microorganisms is collectively known as the microbiota and plays a vital role in training the immune system to distinguish between harmless and harmful substances. The gut provides innate and adaptive immunity to defend against threats while tolerating harmless substances like food and beneficial bacteria. No wonder the gut, with 70- 80% of the body’s immune cells, is the largest immune organ, providing us with a super-efficient immune barrier. Microbiota influence the gut-brain axis mentioned earlier. Dysbiosis, an imbalance in the gut microbiota, can lead to increased intestinal permeability (“leaky gut”), which can trigger systemic inflammation and contribute to various neurological disorders, including anxiety, depression, Parkinson’s disease, and Alzheimer’s disease.
COMMON GUT SYMPTOMS AND DISORDERS: Abdominal pain, bloating, excessive gas, heartburn, constipation, diarrhoea, nausea, and vomiting are common symptoms of gut issues. Changes in stool colour or texture, blood in the stools, difficulty swallowing, unintentional weight loss, loss of appetite, and fatigue can be due to significant gut problems. Common disorders of the digestive system include acidity, peptic ulcers, Gastroesophageal Reflux Disease (GERD), gallstones, infections, inflammation (gastroenteritis, appendicitis, hepatitis, pancreatitis, diverticulitis, etc.) and infestations, Irritable Bowel Syndrome (IBS), Inflammatory Bowel Disease (IBD), food allergies (peanuts, tree nuts, milk, eggs, soy, fish, shellfish, etc.) and intolerances (gluten, lactose, etc.), constipation, haemorrhoids, anal fissure, fistula, and abscess and cancers. The disorders are too many to be discussed here, and prevention is always better than cure.
WHAT MAKES FOOD DELICIOUS? The flavour of delicious food is the perfect balance of five tastes, aroma, and feel (temperature and texture). Gustatory or taste receptors are specialized sensory receptors located on the taste buds of the tongue, but can also exist in other areas of the oral cavity. They can identify the five basic tastes: sweet, salty, sour, bitter, and umami. Capsaicin, the compound that makes chili peppers spicy, is not a taste and temporarily numbs the mouth, affecting our perception of flavours. It is a plant’s painful attempts to defend its seeds. It is perceived as burning and pain by TRPV1 receptors on pain-sensing neurons. Capsaicin is not fully digested and irritates pain receptors in the gut and the anus, causing burning and pain during defecation. Often, excess oil is added to make spicy food tolerable. Hence, spicy chili pepper-containing foods are best avoided.
PREVENTION: Contaminated food or water, especially during floods or drought, inadequate handwashing, especially after using the restroom, improper handling of food, can lead to infection and infestation. Good hand hygiene, thorough washing of fruits and vegetables, and adequately cooked meat, poultry, and seafood help prevent infections and infestations.
A healthy fibre-rich diet of diverse plant-based foods and natural probiotics like curds (yoghurt) eaten in moderation, slowly, and chewed well, supports a healthy gut, microbiota, and promotes health. Managing stress, regular exercise, resisting temptation of oily, sugary, spicy over cooked or processed food, avoiding improper antibiotic use, food allergens and toxins (tobacco, alcohol, mould produced mycotoxins like aflatoxins, bacterial toxins like botulinum toxin (“Botox”) in spoilt food, etc.) and addressing any underlying digestive issues contributes to an efficient gut, endocrine and immune systems, and good physical and mental health.
Dr. P.S.Venkatesh Rao is a Consultant Endocrine, Breast & Laparoscopic Surgeon, and a polymath, in Bengaluru.
