Flatulence is a normal part of healthy digestion but many people think that passing gas (or farting) is embarrassing. Especially if your farts smell bad and you can’t hide them from work colleagues or on a train.

You can get excessive air in the digestive system through:

  • Swallowing air when you eat or drink
  • fizzy drinks
  • chewing gum
  • eating highly fermentable foods like vegetables, beans and wholegrains
  • not chewing your food properly or eating too fast.

If you get excessive gas you could also experience symptoms such as

People who have IBS tend to feel very sensitive to even normal amounts of air (visceral hypersensitivity) so you could feel pain related to the movement of gas.

What are farts made of?

Gases make up 99% of the fart such as carbon dioxide, nitrogen, hydrogen, and methane – most of this isn’t smelly.

Around 74% of the farts is carbon dioxide, hydrogen and nitrogen and is produced by our gut microbes. This means developing a healthy gut microbiome could help if you’re very gassy.

white woman with curly hair, wearing a yellow jumper and jeans holding her nose

What is a normal amount of farts per day? 

Most people pass wind around 15-25 times a day, and this is completely normal. Don’t worry if you feel you never let any out, you probably do in your sleep!

We tend to accumulate gas throughout the day as we eat, which is why you may feel more bloated and gassy at night, but wake up feeling better.

Why do farts smell?

Occasional bad smells are nothing to worry about, but if you’re constantly getting wind that is noticeably odorous you might want to consider what you’re eating, and how you’re digesting your food.

I always ask my IBS nutrition clients if they notice the smell of their farts. I’m interested in whether it’s more like:

  • a rotten eggs odour
  • a cabbage smell
  • just air, no smell

Although this sounds like an odd conversation to be having with another person it does help me!

It gives me an indication of the type of microbes in their guts that could be producing the gasses.

Why do my farts smell like rotten eggs?

The reason farts smell like rotten eggs is most likely because of the presence of hydrogen sulphide. This gas is produced by bacteria that break down food in the digestive system, combining with other gases to form a rotten egg odour.

Sulphur-producing bacteria in your gut create hydrogen sulphide (H2S) and other smelly gases as waste products from the foods you eat.

Microbes which make hydrogen sulphide are confusingly called Sulphate Reducing Bacteria even though they don’t ‘reduce’ it!

Microbes known to create more hydrogen sulphide, and so possibly more farts, in your gut are

These microbes love to feed on foods containing the amino acids methionine and cysteine. Foods high in these amino acids include:

  • Cruciferous vegetables (broccoli, cauliflower, kale, Brussel sprouts)
  • Onions, garlic
  • Eggs
  • Meat
  • Dairy
  • Sulphite containing foods such as wine, dried fruits, and other preserved foods.


close up of a white person's hand clutching bare stomach, black leggings and crop top




Which foods cause farts to smell?

If hydrogen sulphide is an issue for you, these foods could be contributing to the problem of excessive smelly gas:

  • Sulphur rich foods such as broccoli, cabbage, sprouts, onions and garlic
  • Animal product such as eggs, meat, fish, cheese
  • Protein powders which contain cysteine may be converted into sulphur
  • Wine made with sulphides
  • Dried fruits preserved with sulphites
  • Beans and pulses can cause a lot of gas

Beans are well known to cause farts, this is because humans don’t break down the starches very well. Raffinose, found in chickpeas, lentils and other pulses, Brussel sprouts, and cabbage, is one of the complex starches that bacteria ‘eat’ and create gas in the process. 

Removing these foods from the diet might help to improve your symptoms, but it won’t necessarily make the problem go away. You need to tackle the cause of the farts, the bacteria, to get long term improvement. 

Some digestive enzymes contain alpha-galactosidase, which helps breakdown raffinose.

How to reduce smelly farts

To reduce the causes of your excessive flatulence we need to look at the possible causes:

  • SIBOSmall intestine bacterial overgrowth can lead to excessive amounts of methane, hydrogen or hydrogen sulphide. Reducing the bacteria in your small intestine can be done through antibiotics or herbal antimicrobials and changing the way you eat.
  • Large intestine dysbiosis – an imbalance of bacteria in your large intestine could lead to excessive gas or odorous gas production. Adding more fibre to your diet to feed the beneficial gut microbes could help, as well as improving the health of your digestive system. This might include increasing your stomach acid or digestive enzymes to help the food break down.
  • Problems with motility – a slow transit of food through your digestion will allow more time for fermentation and putrification of food waste. Causes could include dietary related constipation, bowel obstruction, gastroparesis (slow emptying of the stomach). 
  • Aerophagia – you could be swallowing too much air as you eat. You’ll also get excess gas through chewing gum, or fizzing drinks.
  • Medicine – if you take frequent pain killers (like ibuprofen or morphine based medication) this can cause more farts.
  • More serious health conditions such as Inflammatory Bowel Disease, Coeliac disease or colon cancer could also lead to farting, so make sure you get checked out by a doctor if you’re worried.

Why do farts smell so bad?

 As well as the non-food reasons above, there are some dietary causes of smelly gas. These include:

  • Carbohydrates – you might be lactose intolerant or sensitive to fructose or other sugars like sorbitol and xylitol. If these sugars are not absorbed in the small intestine during digestion they can reach your microbes in the large intestine which metabolise the sugars causing excessive wind and bloating.
  • High fibre foods – One study found that feelings of bloating increased with a high fibre diet, but the actual amount of gas coming out didn’t increase. Increase fibre slowly, and keep up your water intake as you do so to avoid constipation.
  • Artificial sweeteners – if you bloat with ‘diet’ products you might react to the the sugar alcohols in sugar free products such as xylitol. These aren’t well digested by many people, so this can provide the bacteria with a feast, and they produce gas as a by-product of their metabolism.

Get a personalised nutrition plan for IBS

If you’d like help with bloating, excessive farts my Gut Reset programme could be what you’re looking for. I can help you identify your triggers, work through diet changes to suit your symptoms and lifestyle.

Hi I'm Anna Mapson, registered Nutritional Therapist.

I help people with IBS and SIBO get control of unpredictable gut symptoms to find long term relief from painful and embarrassing IBS without restrictive dieting.

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 better digestion and more energy

Find more about my 3 month 1:1 Gut Reset programme

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