Know Your Body: Why is the gut called the second brain?

Functions of gut

The gut has several important functions. “It breaks down food into smaller particles, absorbs nutrients, transports food through the digestive system, and houses trillions of beneficial bacteria that aid in digestion and support overall health. Additionally, the gut is involved in immune function and produces certain hormones and neurotransmitters,” Dr Nanda Rajaneesh, laparoscopic surgeon, Apollo Spectra Hospital, Bangalore, told indianexpress.com.

Gut microbiota are composed of several species of microorganisms, including bacteria, yeast, and viruses. (Pic source: Freepik)

Why is the gut called “the second brain”?

The gut is often referred to as the “second brain” due to the extensive network of neurons and neurotransmitters present in the gut, known as the enteric nervous system (ENS).

Dr Rahul Dubbaka, consultant gastroenterologist, CARE Hospitals, Hyderabad, shared that the ENS can operate independently of the brain and spinal cord, controlling the movement and function of the gut. “It can communicate bi-directionally with the central nervous system (CNS), which includes the brain, through neural pathways and chemical signals. This gut-brain communication plays a role in regulating digestion, mood, and other aspects of mental health,” he explained.

Connection between the gut and mental health

The connection between the gut and mental health is often referred to as the ‘gut-brain axis or the microbiota-gut-brain axis’. This refers to the bidirectional communication between the brain and the gut, primarily facilitated by the gut microbiota, which is the community of microorganisms living in the digestive tract.

“There is a strong connection between the gut and mental health. The gut produces and houses various neurotransmitters, including serotonin, which plays a key role in regulating mood,” explained Dr Dubakka.

He added that in fact, about 90 per cent of the feel-good hormone serotonin in the body is produced in the gut.

“The gut and brain communicate through the gut-brain axis, involving neural, hormonal, and immune pathways. Imbalances in gut bacteria, inflammation in the gut, or disruption of the gut-brain communication can impact mental well-being and contribute to conditions like anxiety, depression, and irritable bowel syndrome (IBS),” he explained.

Gut health and immunity

Did you know that approximately 70 per cent of immune cells reside in the gut? Yes, that’s right! Hence, for a healthy body, a healthy gut is vital. “The gut-associated lymphoid tissue (GALT) is a significant component of the immune system and plays a crucial role in protecting against harmful pathogens and maintaining immune balance. The presence of diverse beneficial bacteria in the gut also contributes to immune function,” explained Dr Rajaneesh.

He added that good gut health is vital for strong immunity because the gut microbiome interacts with the immune system. A diverse and balanced gut microbiome helps modulate immune responses, promotes the development of immune cells, and helps protect against pathogens. “When the gut is healthy, it can better distinguish between harmful and harmless substances, preventing unnecessary immune reactions,” the surgeon said.

What is a leaky gut?

A leaky gut, or increased intestinal permeability, occurs when the lining of the intestine becomes more porous than usual, allowing substances like toxins, undigested food particles, and bacteria to pass through into the bloodstream. It can be caused by factors such as chronic inflammation, poor diet, stress, certain medications, and imbalances in the gut microbiome.

“Food is digested and broken down into smaller molecules for absorption in the human digestive tract. The digestive system is crucial in defending your body against dangerous toxins. What enters the bloodstream and is carried to your organs is regulated by the intestines’ walls, which serve as barriers,” explained Dr Naveen Polavarapu, senior consultant gastroenterologist, liver specialist and advanced therapeutic endoscopist and endosonologist, Yashoda Hospitals, Hyderabad.

Explaining intestinal permeability, Dr Polavarapu said that there are tight junctions or tiny openings found throughout the intestinal tract that let water and nutrients through while preventing the passage of hazardous substances. How easily chemicals flow through the gut wall is referred to as intestinal permeability.

“It is possible for bacteria and poisons to flow from the gut into the bloodstream when these tight connections between intestinal walls loosen. This condition is sometimes referred to as leaky gut,” he expounded.

When these germs and poisons reach the bloodstream, they greatly increase inflammation and set off an immunological response that has an impact on every cell in the body.

What triggers this leaky gut?

Dr Polavarapu shared the causes triggering leaky gut:

• Abundant sugar consumption: An unhealthy diet high in sugar, especially fructose, damages the gut wall’s ability to act as a barrier.

• Non-steroidal anti-inflammatory medicines (NSAIDs): Ibuprofen and other NSAIDs like it can cause leaky gut syndrome by increasing intestinal permeability.

• Abuse of alcohol: It may make the gut wall more permeable.

90% of the feel good hormone serotonin in the body is produced in the gut. (Pic source: Freepik)

• Nutritional deficits: Increased intestinal permeability has been linked to deficiencies in zinc, vitamin A, and vitamin D.

• Inflammation: Leaky gut syndrome may be exacerbated by persistent inflammation throughout the body.

• Chronic stress: Leaky gut is one of many gastrointestinal illnesses that are influenced by chronic stress.

• Poor gut health: The gut contains millions of bacteria, some of which are helpful and others of which are dangerous. The barrier function of the intestinal wall may be impacted when the equilibrium between the two is upset.

• Yeast overgrowth: Although yeast is naturally found in the gut, an overabundance of it may cause a leaky gut.

Symptoms of a leaky gut

There are several symptoms, and immunological responses brought on by the leaky gut. “Bloating in the stomach, stomach pain, food sensitivity, low energy, joint issues, slow metabolism, skin issues, thyroid issues, mood swings, fibromyalgia, multiple sclerosis, and autism are just a few examples of symptoms,” shared Dr Polavarapu.

Foods that are good for gut health

Dr Harshad Khairnar, gastroenterology consultant, Fortis Hiranandani Hospital, Mumbai, shares foods that are beneficial for gut health.

• Fibre-rich foods: These include fruits, vegetables, whole grains, legumes, and nuts. Fibre helps promote healthy digestion and provides nourishment for beneficial gut bacteria.

• Probiotic-rich foods: These include yoghurt, kefir, sauerkraut, kimchi, and other fermented foods. Probiotics are beneficial bacteria that help maintain healthy gut microbiota.

Kimchi is good for the gut microbiota. (Pic source: Freepik)

• Prebiotic foods: These include garlic, onions, leeks, asparagus, bananas, and Jerusalem artichokes. Prebiotics are types of fibre that feed the beneficial bacteria in your gut.

• Omega-3 fatty acid-rich foods: These include fatty fish (such as salmon and sardines), walnuts, chia seeds, and flaxseeds. Omega-3 fatty acids have anti-inflammatory properties that can support gut health.

• Bone broth: Made from simmering animal bones, bone broth is rich in collagen and amino acids that can help heal and support the integrity of the gut lining.

Foods to avoid for a healthy gut

Certain food items should be avoided or consumed in small quantities for a healthy gut. According to Dr Khairnar they are:

• High-sugar foods: Excessive consumption of sugary foods and drinks can disrupt the balance of gut bacteria and promote the growth of harmful bacteria.

• Processed foods: Many processed foods contain artificial additives, preservatives, and emulsifiers that can negatively impact gut health.

• High-fat foods: Consuming excessive amounts of unhealthy fats, such as saturated fats and trans fats, can promote inflammation in the gut.

• Gluten and dairy products: Some individuals may have sensitivities or intolerances to gluten or lactose, which can cause digestive issues and inflammation in the gut.

• Alcohol and caffeine: Excessive consumption of alcohol and caffeine can irritate the lining of the gut and disrupt the balance of gut bacteria.

“Managing stress levels, staying physically active, getting enough sleep, and avoiding excessive antibiotic use (unless necessary) are also important to maintain gut health. Regularly incorporating probiotic and fermented foods, as well as staying adequately hydrated, can contribute to a healthier gut. Consulting a healthcare professional for personalised advice is recommended,” Dr Rajneesh concluded.

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