The abdominal brain

You mightn’t know it, but you have two brains: a cranial brain and an abdominal brain. Your second brain may not make you smarter, but it does play a vital role in your health. The abdominal brain is no mere agent of the cranial brain and spinal cord. The abdominal brain receives and generates nerve forces, presides over nutrition and is the centre of life itself.

Traditional naturopathic philosophy maintains that if you repair the gut, you will fix up to 80 per cent of human disease. Not only is the gut a system for digestion and absorption, but it has robust mechanisms for control and communication. This means both the nervous and endocrine (hormonal) systems are needed, and the gastrointestinal tract has built-in versions of both. Many diseases are a result of disruption in this communication in the gut itself. The concept of the abdominal brain helps us understand these relationships.


Inside the abdominal brain

There are two “nervous systems” that affect the digestive system and the brain. The vagus nerve is a critical route for information between the cranial brain and the abdominal nervous system. It travels from the brain to the digestive system (and the lungs and thyroid) and is a two-way system for messages to and from the gut.

Not only does the vagus nerve stimulate the digestive system to produce enzymes to digest food, but messengers (such as ghrelin and CCK) travel back along the vagus nerve to stimulate the brain to coordinate energy needs and growth, and regulate appetite. In return, the nervous system exerts a profound influence on all digestive processes.

What is not general knowledge is that the gastrointestinal system also has its own nervous system — the enteric nervous system (ENS) or “abdominal brain”. The abdominal brain is an extensive network of neurons widely dispersed throughout the gut. Together, they coordinate to regulate gastrointestinal events such as peristalsis, blood flow, secretion and absorption.

The abdominal brain also contains all the components we normally consider a part of the cranial brain. It has its own neurons (called glial cells), it produces its own neurotransmitters (dopamine, serotonin, melatonin) and it produces its own neurochemicals (norepinephrine). Additionally, the hormones produced by this abdominal brain have profound effects on the rest of the nervous system. CCK (gallbladder) regulates how hungry we feel and our levels of anxiety while ghrelin (stomach) regulates our food intake and weight and also stimulates the release of growth hormone from the pituitary.


Irritable bowel and migraine

The most common condition we associate with the interaction of the digestive system and the cranial brain is irritable bowel syndrome, where pain and spasms in the gut are exacerbated by stress. Symptoms are triggered by a hypersensitivity reaction of the gut and abnormal communication from the abdominal brain to the cranial brain.

Other conditions such as abdominal migraines are well documented. There are also strong correlations with some forms of epilepsy and with autism and the digestive system. There has been considerable success giving secretin (a gut hormone) to children with broad autistic syndrome, generating marked symptom improvement. The abdominal migraines and abdominal epilepsy are recognised diagnostically by the medical profession, but they’re considered rare, mainly because little attention has been paid to the relationship of the abdominal symptoms associated with these conditions.

A logical explanation for these correlations is that the abdominal brain significantly influences the central nervous system through both nerve reflexes and nerve chemicals produced in the gut. A lot of recent research indicates there is massive overlap of chemical activity in the digestive system and the brain, involving both these nervous systems.


Nerves in the ‘mini-brain’

The abdominal brain is structurally and functionally complex and is located within the walls of the gastrointestinal tract. It’s sometimes known as the “mini-brain” because it shares important features with the central nervous system. For example, both nervous systems have a common embryological origin and several neurotransmitters (serotonin, opiates, cholecystokinin (CCK) etc) are produced in both the brain and the gut wall.

Under normal circumstances, the gut provides sensory information to the central nervous system (the CNS) and the CNS affects gastrointestinal function. However, the human gastrointestinal system, even if deprived of CNS innervation, is capable of coordinated digestion, mobility, secretion and absorption through the activity of neurons in the enteric nervous system and cells in the gastrointestinal tract.

Usually, the abdominal brain automatically controls gut functions such as motility, absorption and secretion, independently of the CNS. But the CNS often influences the functions of the ENS. Events such as acute inflammation or infection can cause long-lasting or even permanent changes in the structure and function of the abdominal brain. For example, inflammation or infection can destroy abdominal motor neurons, resulting in cramps, spasms and pain in the gut.


Abdominal brain chemicals

Chemicals that communicate between nerves are not only produced in the central nervous system. A large proportion of their production is in the digestive system. That makes sense, since neurotransmitters are formed from amino acids, which are the breakdown products of our food proteins through digestion. The abdominal-brain neurons produce and secrete a large range of neurotransmitters: acetylcholine (excitatory), norephinephrine (inhibitory), dopamine, serotonin and melatonin.



Melatonin was thought to originate in the pineal gland and be secreted during the night, but recent studies show the gut is a much larger source and it has major effects on the gut.

Melatonin is discharged into the gut and induces the secretion of CCK (cholecystokinin, the neurohormone that triggers the gall bladder to secrete bile at the gut level). CCK also triggers the feeling of fullness (from the brain) and (if levels are abnormal) is implicated in anxiety states. Melatonin is also highly protective against inflammation and damage of both the stomach and the pancreas. So melatonin accelerates healing of ulceration, reduces gastritis and pancreatitis and is antioxidant and anti-inflammatory.



Serotonin is found throughout the human gastrointestinal tract as well as in the bloodstream and the brain. It controls many important physiological functions including inflammation, neurotransmission, gastrointestinal motility, blood clotting and cardiovascular integrity.

Serotonin is also one of our major “happy hormones” and low levels of this hormone are potentially one of the major connections between mood disorders and digestive symptoms. Ninety-five per cent of the body’s serotonin is synthesised in the neurons of the gut and released by stimulation of the vagus nerve. It’s also synthesised by the mast cells and platelets in reaction to allergy-causing substances.



Dopamine is regarded as an important regulator of intestinal function as it regulates bicarbonate secretion in the small intestine and thus reduces the risk of duodenal ulceration. About 50 per cent of the body supplies of dopamine are produced in the gut. Dopamine and noradrenaline control many functions in microglial cells. These neurotransmitters are produced from the amino acids phenylalanine and tyrosine.


Norepinephrine — the effect of stress on the gut

About 45 to 40 per cent of the total body production of norepinephrine occurs in the abdominal brain. Stress causes norepinephrine to be released, and exposure to stress results in decreased production of immunoglobulin A (IgA). Low levels of IgA disrupt the mucous membrane of your intestines, making you prone to food allergies and immune disorders. The higher your norepinephrine levels, the lower your IgA levels.

Test-tube experiments have also shown that several neurochemicals have the ability to directly enhance the growth of disease-causing micro-organisms in the gut. Norepinephrine has been shown to increase growth of Escherichia coli (E. coli), which is implicated in gastrointestinal, respiratory and urinary tract infections.


Gastrointestinal hormones

Gastrointestinal hormones are chemical messengers that regulate intestinal and pancreatic function. These hormones are secreted in reaction to specific stimuli. As well as their hormonal function, gastrointestinal hormones also serve as agents that transmit nervous impulses. These “neurohormones” include ghrelin (from the stomach) and cholecystokinin (CCK) from the small intestine. Some of the functions of CCK have already been discussed, but ghrelin is an interesting case study.



Ghrelin was recognised in 1999 as both a gastric hormone secreted by the cells of the stomach, and also as a mediator of growth hormone release in the pituitary gland. Growth hormone builds the body and the function of ghrelin is to coordinate energy needs with the growth process and help maintain balance in the body. Ghrelin is essential for regulation of growth and metabolism.

Abnormal levels of ghrelin are involved in a variety of altered energy states such as obesity, eating disorders, cancers and general malaise. It increases hunger and also enhances the immune system, reduces inflammation and safely increases heart output.

Ghrelin has a variety of functions central to health throughout the body and it largely comes from your abdominal brain.


Treating the abdominal brain

Given that the abdominal brain is so important to our overall wellbeing, it’s essential to look at how to support it in a holistic way.

The bacteria in your gut and your overall health are inextricably linked. The gastrointestinal tract, the largest surface area of the body, is constantly exposed to micro-organisms, with the gut flora (organisms in the gut) being considered an organ of the human body in its own right. Humans coexist in a symbiotic relationship with an estimated 300–500 different species of bacteria in the gut.

This symbiotic relationship provides unique benefits and plays a critical role in intestinal function, including intestinal immunity and the abdominal brain. The correct microflora balance is essential for the presence of clearly defined lines of communication and the health of the whole system, including the immune and the nervous systems.

To treat the gut and enhance your health, it’s important to eat foods to reduce the amount of harmful organisms and then promote the growth of healthy bacteria.

Garlic (Allium sativum) is excellent for regulating abnormal gut bacteria — providing antibacterial and antifungal actions, giving it broad-spectrum antimicrobial activity in the gut. Broad-spectrum herbal or food antimicrobials are excellent for removing pathogenic organisms, as they don’t create imbalances in the normal bowel microflora.

Pau d’arco is a herb that also possesses a broad-spectrum antimicrobial activity, especially against protozoa and fungi, and appears to have a capacity to kill micro-organisms rather than merely inhibit their growth. It also protects the correct lactobacilli.

Green tea and other tannin-containing herbs have an antimicrobial effect and encourage the growth of the correct lactobacilli and bifidobacteria.

Ginseng (Panax ginseng) reduces inflammatory activity in the gut, reduces the growth of abnormal, harmful micro-organisms as well as reducing the damaging effects of stress on the gut and on the central nervous system. The chemicals that give ginseng its effect, the ginsenosides, are activated by bifidobacteria in the gut. Ginseng increases immune status and assists in the maintenance of homeostasis of the nervous and hormonal systems.

Prebiotics such as slippery elm are administered to provide a food source for the correct bowel bacteria. These are herbs and foods that contain mucilages, polysaccharides and fructo-oligosaccharides (FOS). Slippery elm bark, marshmallow root and psyllium husks are good mucilage sources. Natural food sources of FOS include bananas, Jerusalem artichokes, onions, asparagus, and garlic. Inclusion of these complex carbohydrates (fructans) in the diet enhances gut health by providing an energy source for bowel flora. They also improve nutrient absorption and reduce inflammation. Mucilaginous herbs will encourage the growth of beneficial bowel flora.

Probiotics are bacteria we need in our gut. They include lactobacilli and bifidobacteria and are a major part of the normal intestinal microflora of humans. The correct balance of these intestinal bacteria is vital to protect the host against colonisation by harmful organisms and the associated inflammatory and infective diseases. Healthy bowel bacteria also manufacture many critical nutrients, such as folic acid and vitamin B12, that are essential for correct nervous system function. Lactobacilli and bifidobacteria taken orally will correct bacterial overgrowth, stabilise mucosal barrier function and enhance immunity.

Healing the abdominal brain — a quick guide


  • Eat moderate amounts of high-quality protein to provide the amino acids necessary for neurotransmitter production. Balance proteins by using fish, animal and vegetable sources.
  • onsume a diet high in vegetables and moderate fruit (be careful of sugars).
  • Organic food is important, as it generally has better nutrients and less chemicals.
  • Avoid refined sugars and refined carbohydrates.
  • Avoid foods you are intolerant of, the most common being wheat and dairy (although yoghurt is often acceptable).
  • Plain yoghurts can be useful if they have adequate live lactobacilli and bifido cultures and low sugar.

    Useful supplements

    • Probiotics — lactobacilli (acidophilus, rhamnosus), bifidobacteria — are good.
    • Inulin/fructo-oligosaccharides encourage growth of lactobacilli.
    • Zinc, magnesium, vitamin B4 and vitamin C promote correct metabolic pathways of neurotransmitter and hormone production.
    • Magnesium and calcium balance is important to stabilise overactivity of the nervous system.
    • Vitamin A supports mucosal repair.
    • Essential fatty acids, especially omega 3 from fish oil, reduce inflammation.
    • L-tryptophan assists with correct serotonin/melatonin production.
    • L-tyrosine is the basis for dopamine production (with witamin C).
    • L-Glutamine repairs gut membrane, is an energy source for the small intestine, is a basis for GABA and L-glutamate and balances blood sugar.

      Useful herbs

    • Ginsengs including Korean (Panax ginseng) and Siberian (Eleuthrococcus senticocus) support adrenals and manage stress.
    • St John’s wort (Hypericum perforatum) supports serotonin balance.
    • Slippery elm (Ulmus fulva) assists with mucosal repair and lactobacilli growth.
    • Herbs such as meadowsweet (Filipendula ulmaria), Chinese wormwood (Artemesia annua), olive leaf (Olea europa) and pau d’arco (Tabebuia avellanedae) can be useful to reduce an overgrowth of pathogenic organisms.
    • Meditation, yoga, tai chi or stress management techniques are all useful.

      Avoid antibiotics unless absolutely necessary as these adversely alter gut microflora.


      First treat the gut

      Health is the end result of a complex interplay of various factors, including gastrointestinal health, endocrine health and neurological health. Taking the human body as a whole system, healthy relationships between all the parts are crucial to the health of the whole.

      While the research on the abdominal brain is still in its infancy, this field is confirming the systemic and interactive nature of the body. This goes a long way to support the holistic nature of our beings. It’s an exciting field for the future and reinforces the old axiom: treat the gut first (to achieve health of the body/mind).

      References available on request.

      Dr Karen Bridgman is a naturopath practising at Pymble Grove Clinic (Sydney) and lecturing in the Masters Degree in Herbal Medicine at the University of Sydney.

The WellBeing Team

The WellBeing Team

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