Irritable bowel syndrome, serotonin levels and the role of diet

Irritable bowel syndrome (IBS) is becoming an increasingly common gut disorder in which the sufferer typically experiences: abdominal pain, cramping, bloating, excess wind, diarrhoea, and/or constipation, or an alternating combination of the two. Whilst the severities of these symptoms vary considerably between individuals, IBS has a profound effect on the sufferer’s quality of life. Many of the day to day activities that the majority of us take for granted can pose much more of challenge when you have IBS. You no longer simple take your body for granted, with careful forward planning essential in order to cope with the unpleasant, and often, embarrassing symptoms. Understanding IBS and what triggers the variety of symptoms is paramount to developing coping strategies.

It is thought that people with IBS have an abnormal gastrocolic response. This is the physiological reflex that controls the movements of the gastrointestinal tract (GI tract). Simply put, this mechanism controls the movement (peristalsis) that pushes food through and out of the gut. In IBS, simply eating or drinking can cause an over reaction of this process resulting in painful cramps, often resulting in diarrhoea.

Whilst the action of eating causes an increase in gut mobility, eating large meals seems to cause excessive cramping and bouts of diarrhoea, so a key tip is to try to eat small amounts and to try to eat regularly. Many people with IBS also find there are specific dietary triggers that can result in discomfort and bowel dysfunction. Knowing what foods to include, and what foods to avoid, can make a dramatic impact on regulating or avoiding specific symptoms.

Several gut peptides (types of protein), and neuropeptides are involved in the control of the gastrocolic reflex, of which serotonin is one such example. Serotonin, a neurotransmitter peptide, is generally known for its role in the regulation of mood, appetite, sleep, and some cognitive functions including memory and learning. However approximately 80% of the serotonin is actually produced in the body by the enterochromaffin cells found in the gut lining. The function of serotonin within the gut is to control muscle contractions, thereby functioning to maintain the movement of the intestines. Importantly however, many IBS sufferers can directly link stress to the onset of symptoms and it appears that there may, in some cases, be a link between serotonin, stress and IBS.

During a stressful experience there is a complex set of interactions between the hypothalamus (a part of the brain), the pituitary gland (also part of the brain) and the adrenal glands (at the top of each kidney). Several types of neurotransmitters are involved in this system, collectively known as the HPA-axis, which is thought to be dysfunctional in individuals with several conditions including fibromyalgia, chronic fatigue syndrome and depression to which IBS is often linked. Sufferers of these conditions can have numerous abnormalities in their hormonal, metabolic and brain-chemical activity including levels of serotonin. Dysregulation of the serotonin system has been found in individuals with IBS, with low levels associated with constipation, and high levels with diarrhoea (Sikander et al, 2009).

The link between stress, diet and IBS means that suffers can help reduce symptoms not only by modifying their diet, but also from reducing tension and stress through simple relaxation techniques such as: meditation, yoga and the Alexander Technique. Certainly living with IBS is far from pleasant, but with the right diet and learning how to manage stress, there is no reason why IBS should not be controllable. Let you control your IBS and not your IBS control you!

Complex carbohydrates, also known as starchy foods, are broken down slowly in the body to produce energy and are much kinder to the GI tract. This includes foods such as rice, oats and barley as well cooked vegetables.
Avoid foods high in fast releasing sugars such as unrefined grains, confectionary, cakes and biscuits. Avoid raw vegetables, salads and raw fruit.
Increasing omega-3 from oily fish (mackerel, sardines, pilchards, salmon) or through supplements can help alleviate inflammation and calm the guts. Try including evening primrose oil as a source of GLA, an anti-inflammatory omega-6 fatty acid
Avoid saturated fats from red meat and dairy food and fried food as these are classic triggers that exacerbate the symptoms of IBS
Lean chicken, pork, turkey and fish can supply good animal protein.
Avoid protein from red meat.
Soluble fibre absorbs excess fluids forming a gel which bulks out faeces and can therefore help to reduce diarrhoea. By bulking out faeces, soluble fibre keeps the muscles of the GI tract gently stretched thus giving them something to grip on during a peristaltic motion and helps to avoid painful spasms. This in turn can help relieve constipation by softening and pushing through any impacted faecal matter.
Insoluble fibre (bran, raw fibrous vegetables, salad greens, unpeeled fruits) can trigger painful gastrointestinal spasms
Drink plenty of fluid to avoid constipation. The following teas can help eliminate gas and bloating but also can relax the intestine smooth muscle: peppermint, fennel, ginger and chamomile.
Coffee, tea (even decaffeinated) and alcohol are powerful GI tract irritants, and can have the same effects as fats and insoluble fibres. Also avoid sugary carbonated drinks or drinks containing the sweeteners sorbitol or xylitol.
Available as dietary supplements and foods such as yogurt, with most products containing one of two types of bacteria – Lactobacillus or Bifidobacterium. Probiotics are often combined with prebiotics to form synbiotics. Prebiotics are simply non-digestible food ingredients that selectively stimulate the growth and activity of beneficial microorganisms already in the colon.

Sikander A, Rana SV, Prasad KK. (2009) Role of serotonin in gastrointestinal motility and irritable bowel syndrome. Clin Chim Acta. 403:47-55.


  • Atkins Diet have helped me a lot to maintain a very good physique. My mom is also on an Atkins Diet. “

  • Ruth Spicer

    Hi Nina, I spoke to you at the conference, after your very interesting presentation about the blood type diet. Here is the information about the books.
    ‘Eat Right For Your Blood Type’ – Complete Blood Type Encyclopedia – by Dr Peter J. D’Adamo
    He has also written ‘Live Right For Your Type’ Iam sure you will find them very interesting
    It certainly fitted in with what you were talking about

  • Ruth Spicer

    I am a great believer that diet has a huge role in IBS as in many other diseases. We are what we eat!

  • Hi Jasmine, I have no doubts that the Atkins diet works, my concerns are for the long term internal consequences that may be less obvious!

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