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
  • 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 and should they smell?

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.

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

I ask my IBS nutrition clients if they notice the smell of their farts, and whether it’s more like

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

This gives 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 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. In most cases, you don’t need to do anything about the smell. Sulphur-producing bacteria in your gut create hydrogen sulphide (H2S) and other smelly gases as waste products from the foods you eat.

Hydrogen sulphide producing bacteria are confusingly called Sulphide Reducing Bacteria even though they don’t ‘reduce’ it! They love to feed on sulphur containing foods such as

  • Cruciferous vegetables (broccoli, cauliflower, kale, Brussel sprouts)
  • Onions, garlic
  • Eggs
  • Meat
  • Dairy


close up of a white person's hand clutching bare stomach, black leggings and crop top
Which foods cause farts to smell?
  • 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 excessive gas, this is because humans don’t break down the starches very well. Raffinose is one of the starches that bacteria ‘eat’ and create gas in the process.

How to reduce smelly gas

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

  • SIBOSmall intestine bacterial overgrowth can cause 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.
  • 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 farting.
  • 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.
Dietary causes of smelly farts
  • 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 gas 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, 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

“Anna is amazing! I feel totally transformed"

Find more about 1:1 Gut Reset programme

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