If you have IBS you may also experience fatigue. In fact around 60% of people with IBS experience extreme exhaustion, and fatigue is the third most common non-digestive complaint.

This is more than just tiredness, it’s feeling weak, ill and completely lacking in energy.

Here are ten common causes of fatigue in IBS.

1. Anaemia and IBS

Anaemia and IBS are both very common, so sometimes you have both. Some studies have shown a higher prevalence of iron deficiency anaemia in patients with IBS compared to people who don’t have it.

There is no evidence that IBS causes anaemia.  If you are prone to a very fast transit time food may be passing through you quicker than you can absorb the nutrients you need.

You can become anaemic due to other gut disease such as coeliac disease, Inflammatory Bowel Disease, or diverticular disease. It’s important your doctor is involved in understanding what is going on in your digestion.

Don’t take iron supplements unless you have low iron stores. Get tested before taking iron supplements. If you need to increase your iron try a supplement with iron bisglycinate, rather than ferrous sulphate, or ferrous fumarate which commonly cause cramping, constipation or stomach aches. 

We know that cells in your gut can up regulate iron absorption when needed, and these may be affected by gut bacteria.

You can increase your iron intake through dietary changes like eating meat, fish, eggs, and green leafy vegetables and lentils.


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2. Low functioning thyroid can cause fatigue in IBS

Our thyroid releases hormones which controls our cell metabolism, so affects how quickly each cell does it’s work. It’s common that IBS and hypothyroidism go hand in hand, and some reports even suggest SIBO may be present in more than half of patients with hypothyroidism.

Hypothyroidism can slow your digestive motility causing constipation, nausea or reflux. A low functioning thyroid may also give you severe fatigue, both of which can be confused with IBS.

Ask your doctor for a full thyroid panel blood test or find a thyroid specialist Nutritional Therapist to support you. 

3. Chronic Fatigue Syndrome and IBS

Persistent fatigue that lasts for over six months and isn’t better when you rest could be CFS. If you’re also experiencing migraines, sore lymph nodes, flu-like aching or muscle pains, palpitations or sleep problems the fatigue could be related to CFS.

One of the most common causes of IBS is post-infectious inflammation which leads to ongoing digestive issues. One study found people infected with Giardia lamblia in Norway had increased risk of both IBS (43%) and CFS (26%) 10 years after the infection. 


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4. Fatigue in IBS can be caused by undereating

If you are over restricting your diet, either due to food anxiety, or trying to avoid reactions, you may not be eating enough food. 

If you don’t have enough protein, fats and carbohydrates you can begin to feel very weak, have sleep problems, or a low mood. 

Try using a diet diary to see what you’re eating in a week, and look at whether you’re low in any major food groups. 

5. Poor diet in IBS can cause fatigue

Maybe you’re eating enough food, but it’s not the sort of food that is really giving your body the nutrients that it needs. 

You could be low in iron, protein, or carbohydrates which all help to give us energy. Surviving on processed foods low in essential vitamins and minerals can lead to fatigue. 

Working with a qualified nutritionist can help to identify how to broaden your diet variety in a way that doesn’t trigger symptoms. 


6. Sleep problems can be worse for people with IBS

If you’re not getting around 8 hours of quality sleep you may feel very tired. People with IBS seem to have poor sleep, but there is limited evidence as to why. Some people with IBS wake more frequently during the night.

It could be blood sugar management, poor diet, anxiety, abdominal pains or other GI symptoms. 

We feel more pain when we are very tired, feel more anxious and have increased hunger hormones. This can make us crave starchy foods for a quick glucose fix. Some people report more abdominal pain, anxiety, and fatigue after a bad night’s sleep. 

Sleep hygiene tips like reducing stress, exercise, having  dark room, and blocking blue light before bed can all help improve your sleep quality. 


7. Anxiety and IBS can increase fatigue

Fatigue is linked to more severe IBS symptoms, worse Quality of life scores, distress, anxiety sensitivity, and perceived stress. When we’re anxious we tend to feel exhausted, due to the tension in muscles, lack of sleep and constant hypervigilance. 

Prolonged exposure to stress can leave us low in B vitamins and Magnesium, both of which are needed for energy production.  Anxiety and stress can also de-prioritise digestion, meaning that your bloating, gas and cramps can increase. 

8. Inflammation in IBS is associated with fatigue

We know that people with IBS may have a higher count of Mast Cells in the gut. These are cells that can activate an immune response when triggered by an allergen, gut microbes, pathogens or other immune complexes. 

Higher levels of mast cells in the gut are associated with increased fatigue and people with IBS who had a higher immune activation in the colon had higher anxiety and depression. Mast cells may also trigger your nervous system, increasing abdominal cramps and pains. 

Resolving this low level inflammation in the gut can take time, but diet and lifestyle changes can play an important role in feeling better. Improving your gut microbiome can help address some of the triggers for mast cell activation. 


9. Inactivty could be driving IBS fatigue

Regular exercise might be the last thing on your mind when you’re feeling exhausted, but regular movement, however small, has been shown to improve fatigue. Moving your body also helps to reduce anxiety, which can be raised in people with IBS.

You don’t need to be climbing mountains or doing Cross Fit, just a simple slow walk or some quiet yoga at home can be a good first start. 


Hi I'm Anna Mapson, registered Nutritionist (mBANT, CNHC). I help people with IBS, SIBO, reflux and other gut health issues.

I can help you to:

  • understand your digestion better, so you recognise your triggers
  • eat a well balanced diet, with tasty meals that are simple to prepare
  • develop healthy, sustainable habits for life

“Anna is amazing! I feel totally transformed"

Find more about 1:1 IBS nutrition consultations