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What's causing your bad digestion?

Notebook on a white table surrounded by an array of foods
The most common causes of poor digestion and what you can do about them. Including diet, alcohol, painkillers, caffeine and eating too late at night.

You may think you’re eating healthily and mindfully, but does your digestive system disagree? We look at what else could be going on…

We’re all aware of certain poor eating habits or types of food that are likely to cause digestive distress.

Bolting down lunch can result in an afternoon of bloating and flatulence; while a ‘who can eat the hottest curry’ competition could leave you locked behind the bathroom door with stomach problems.1,2

Sometimes, however, it’s less easy to work out what’s behind indigestion, heartburn, stomach ache or other digestive problems.

In this article, we'll explore the impacts of the following on your digestion: 

Going overboard on fibre

We’re often told to increase the fibre in our diets for better digestion.3

But suddenly and significantly increasing the amount of fibre you eat can be a shock to your digestive system, and lead to flatulence, constipation and discomfort.4

What you can do about it: Always increase fibre in your diet gradually to give your body time to adjust. And make sure you drink more water too, as fibre absorbs fluids so this will help keep your stools soft.5

Handpicked content: 11 constipation remedies

A boozy night

Alcohol irritates your digestive system by producing more stomach acid than normal.6

This can lead to acid reflux and an inflamed stomach lining.7,8

Alcohol also reduces the number of digestive enzymes our bodies produce, which means we may not absorb the nutrients we need to break down our food properly.9

What you can do about it: Stick within the weekly limit of 14 units for alcohol and limit the total amount you have in one day. Alternatively, steer clear altogether.10

Handpicked content: Your guide to digestion

A little too much caffeine

Some people are sensitive to caffeine and find it increases the production of acid in their stomach, triggering heartburn.11

Coffee also has a laxative effect. A study of 12 healthy people, published in 1998 in the European Journal of Gastroenterology & Hepatology, found that a cup of black coffee had the same power to stimulate the muscles of the colon as tucking into a meal.12

What you can do about it: Cut down on caffeinated tea and coffee, and watch for ‘hidden’ sources of caffeine, for example in chocolate, energy drinks and some medicines.13

Handpicked content: Is caffeine good for you?

A smoking habit

Smoking attacks the sphincter muscle at the end of the oesophagus, which prevents acid from travelling out of the stomach.

Cue acid reflux, which can lead to ulcers and inflammatory bowel conditions.14

What you can do about it: Quit smoking today. Ask your GP about the NHS’s Smokefree programme.

Taking certain painkillers

Non-steroidal anti-inflammatory painkillers (NSAIDs), like ibuprofen and aspirin, may irritate the gut lining by weakening its defences against the acid in the stomach.

This can lead to ulcers or bleeding. And taking NSAIDs can also weaken the oesophagus’ sphincter muscle – increasing the chances of heartburn.15

What you can do about it:  Ask your GP to review the medications you’re taking.

Eating late at night

Our bodies digest best in an upright position.

This means that lying down in bed soon after eating makes it far easier for stomach acid to travel up the oesophagus, causing heartburn.16

What you can do about it: Help your digestive system by allowing three to four hours after eating before lying down so your stomach can empty.

In a 2003 study published in Gut, researchers found that stomach gas was expelled faster when participants were in an upright position than when they lay on their backs.17

If heartburn still troubles you in bed, try propping your shoulders up on pillows, or raise the head of your bed so your chest is higher than your waist.18

Overdoing the vitamin C

We need vitamin C every day but some people find taking large amounts in supplement form – usually more than 1000mg – can cause diarrhoea, flatulence and stomach pains.19

What you can do about it: Always read the label and follow the correct dosage instructions. You can also try a ‘buffered’ vitamin C supplement that has minerals added to make it easier on sensitive digestions.20

Handpicked content: Vitamin C: Why we need it and where to get it

Is stress stopping your digestion?

When you’re feeling stressed, it’s normal to experience symptoms like insomnia or to find yourself relying on coffee to get through the day.

But stress can also affect your digestion, which can have a serious knock-on effect.

When our digestion is out of balance, we may not produce enough stomach acid.

This means we might not be able to absorb nutrients properly from our food, leading to a lack of vitamins and minerals.21

Handpicked content: Comprehensive guide to stress

The importance of vitamin B12

Vitamin B12 has a number of important roles, mainly helping our bodies convert food into energy.

It can also help produce red blood cells to transport oxygen around the body, and helps keeps the brain and nervous system healthy.

We can’t naturally make B12, so we need to get it from foods such as meat, fish, eggs, and dairy, or supplements.

You can also find B12 in fortified cereals, soy products and some plant milks.

The trouble with vitamin B12 is that we rely on stomach acid to help us absorb it – and up to a third of us aren’t making enough.

Handpicked content: 34 top foods & sources of vitamin B12

B12 and stomach acid

The B12 we get from food comes attached to protein.

Before it can be absorbed and used by the body, this bond must be broken – by stomach acid.

It then has to bond to another protein called intrinsic factor, produced by the same cells that produce stomach acid.

However, issues such as bacterial infections, thyroid problems, and ageing can all cause production of stomach acid to nose-dive.

In fact, by the time we reach our fifties, 10-30% of will struggle to absorb B12 from food, thanks to low levels of stomach acid.22

Stress is particularly tough on our digestion.

The body’s stress response diverts blood away from the digestive system and towards the muscles to prepare us for ‘fight or flight’.

This may affect our stomach acid in one of two ways, either by increasing or decreasing production.

In a study of 14 healthy men published in the journal Digestive Diseases and Sciences in 1990, mental stress increased gastric output (stomach acid) in about half the volunteers, but decreased it in the other half.23

So tackling any sources of stress should be your first step to rebalancing your stomach acid levels.

Handpicked content: Comprehensive guide to stress: Causes, symptoms and effects

Increase your B12 intake

The NHS recommends adults get at least 1.5mcg of B12 a day.

However, if your stomach acid levels are low, you may need more.

If you are lacking in B12, you may experience:

  • extreme tiredness
  • lack of energy
  • muscle weakness
  • dizziness or loss of balance
  • reduced sensitivity to pain or pressure
  • pins and needles or numbness
  • visual disturbances
  • pale, yellowy skin

34 top foods & sources of vitamin B12

34 top foods & sources of vitamin B12

A key nutrient that our bodies can’t produce on our own, vitamin B12 is supported through our diet and with supplements.

But what is vitamin B12? Why is it important? And what are some of the best vitamin b12 sources?

Sort low acid levels

You can also take steps to rebalance your stomach acid.

Some practitioners suggest drinking diluted lemon juice or apple cider vinegar to increase stomach acidity, or you could try taking a digestive enzyme that contains betaine hydrochloric acid (betaine HCI).

In a pilot study of six volunteers carried out by the University of California in 2013, 1500mg of betaine HCI was found to help lower gastric pH, which, in turn, may increase stomach acid production.24

Talk to your GP if you suffer from digestive discomfort and would like to try complementary remedies.

The secret to understanding what triggers your digestive upset

When your digestive system isn’t working properly it can cause constipation, diarrhoea, indigestion and acid reflux.

If these sound familiar to you, don’t worry- these are very common issues.

Poor digestive health can also be the cause of more serious conditions such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS).

However, most digestive complaints can be remedied with changes to your diet, once you have identified what might be causing your flare-ups.25

Handpicked content: Nine foods to avoid if you have irritable bowel syndrome (IBS)

Even if you only suffer from digestive discomfort occasionally, it is well worth paying attention to your gut and what it is trying to tell you.

Perhaps you are sensitive to certain foods or drinks that you include in your diet. Perhaps you eat too much, too little, too fast or at the wrong times.

Eating a varied diet rich in fruit, vegetables and wholegrains, not smoking and only drinking in moderation are great first steps in taking care of your gut.

However, it is a good idea to see if you can get a better understanding of your gut to see what personally works best for you.

Handpicked content: Promoting good digestion and understanding food allergies

Keep a food diary

For a period of two weeks, keep a record of everything you eat and drink.

Include the time of day you had it, and make a brief note about what is going on at that time.

For example, if you are wolfing down a sandwich between meetings, eating sweets in the car or indulging in a midnight snack- it is all relevant.

Try to give an idea of the quantity of food consumed. Bear in mind that portion sizes are often smaller than we think!

For example, a portion of dry pasta is 75g, the equivalent of a couple of handfuls or a small bowlful.

Your smartphone can help. There are many free apps on the market that can help you track your digestion.26

How to keep a food diary


Write down everything you eat daily

Include the time you ate it, and the severity and time of any symptoms on that day.


Look out for patterns

Is there a pattern where eating a certain food seems to regularly coincide with a rise in your symptoms? If so, consider eliminating this from your diet for a few weeks.


Gradually reintroduce foods in small quantities

This allows your body to adjust and accept foods it may be more sensitive to. Record any changes in your symptoms. This will identify how much you can eat without triggering a reaction.


Repeat with other foods

If necessary, repeat these same steps with other foods that may be triggering your digestive issues. 

Analysing your results

Wheat, fizzy drinks and dairy are common causes of bloating, as is alcohol.

In fact, alcohol, caffeine and smoking are all risk factors for those with a sensitive stomach, and should be eliminated if possible, at least to see if your symptoms improve.

Greasy, spicy and fatty foods found in many fast food and takeaways play havoc with your digestion, so consider cutting these out or look for healthier alternatives if they seem like a trigger for you.

Vegetables such as onions and cabbage, as well as beans can cause excess wind and bloating, as well as beans and pulses.

However, these foods are healthy so it is not advisable to cut them out completely, but rather to eat them in small quantities and build up your tolerance.

You might find that some of your eating is stress or boredom-related.

When you are eating for reasons other than hunger, it is likely to lead you to you making poor choices without putting your digestive health first.

If you find yourself craving sugary foods in front of the TV an hour after dinner, then take a look at your lifestyle and consider a walk after your evening meal, or a hobby that gets you out of the house so you aren’t tempted to make bad food choices out of habit.

The advice in this article is for information only and should not replace medical care. Please check with your GP or healthcare professional before trying any supplements, treatments or remedies. Food supplements must not be used as a substitute for a varied and balanced diet and a healthy lifestyle.

Last updated: 7 October 2021


  1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886943/
  2. www.nhs.uk/live-well/eat-well/good-foods-to-help-your-digestion/
  3. www.nhs.uk/conditions/constipation
  4. https://www.guysandstthomas.nhs.uk/resources/patient-information/gi/increasing-the-amount-of-fibre-in-your-diet.pdf
  5. https://www.webmd.com/digestive-disorders/features/bloated-bloating#1
  6. https://www.drinkaware.co.uk/alcohol-facts/health-effects-of-alcohol/effects-on-the-body/is-alcohol-harming-your-stomach/
  7. https://www.drinkaware.co.uk/alcohol-facts/health-effects-of-alcohol/effects-on-the-body/is-alcohol-harming-your-stomach/
  8. https://www.nhs.uk/conditions/Indigestion/
  9. https://www.drinkaware.co.uk/alcohol-facts/health-effects-of-alcohol/effects-on-the-body/is-alcohol-harming-your-stomach/
  10. https://www.drinkaware.co.uk/alcohol-facts/alcoholic-drinks-units/latest-uk-alcohol-unit-guidance/
  11. www.nhs.uk/live-well/eat-well/good-foods-to-help-your-digestion/
  12. https://www.ncbi.nlm.nih.gov/pubmed/9581985
  13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445139/
  14. https://www.nhs.uk/live-well/eat-well/five-lifestyle-tips-for-a-healthy-tummy/
  15. https://www.hopkinsmedicine.org/healthlibrary/conditions/digestive_disorders/medications_and_the_digestive_system_85,P00389
  16. https://www.nhs.uk/conditions/Indigestion/
  17. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1773697
  18. https://www.nhs.uk/conditions/heartburn-and-acid-reflux/
  19. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-c/#what-happens-if-i-take-too-much-vitamin-c
  20. http://blogs.oregonstate.edu/linuspaulinginstitute/2015/05/28/questions-about-vitamin-c/
  21. https://universityhealthnews.com/daily/digestive-health/low-stomach-acid-the-surprising-cause-of-many-indigestion-symptoms/
  22. https://www.hsph.harvard.edu/nutritionsource/b-12-deficiency/
  23. https://link.springer.com/article/10.1007/BF01537249
  24. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3946491/
  25. https://www.nhs.uk/Livewell/digestive-health/Pages/gut-health.aspx.
  26. https://www.everydayhealth.com/digestive-health-pictures/mobile-apps-for-digestion-tracking.aspx.

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