In an age when our bodies’ every input and output is micro-measured and critiqued, how often should a healthy human fart?

Those who can list off how much fruit and vegetables should be consumed on a daily basis; how much water should be considered a minimum; how much alcohol a maximum, are typically at a loss to understand and contextualise the resulting wind.

Even broaching the topic for the over-16s strays into toe-curling territory: a starch-collared, Victorian prude would have been more likely to openly discuss his married sex life than some of us are willing to confess our daily exhaust emissions.

“From what I’ve found, 10 times a day is normal to fart, but up to twice that can be considered normal, with a big range in the volume as well,” says Dr Beth Mallard, lecturer in physiology at NUI Galway.

“I can’t imagine any sort of healthy diet, in any conventional sense, that would not produce any gas, as you have gas that is produced separate to what you eat. So everyone is going to fart, whether they’d like to acknowledge it or not.

“Gas accumulates in your gastrointestinal tract. Some of this is swallowed when you’re eating, while other gas is formed from chemical reactions, but most of it is formed from the bacteria in your gut,” says Mallard.

In addition, we differ hugely in the amount we fart because the bacteria population in our gut varies hugely between people, and those populations react differently to different foods.

Take that timeworn old-reliable of fart-feeding culprits: beans (think Blazing Saddles). Should you suddenly increase your intake, the fibre won’t be properly digested, but your gut bacteria will ferment it instead.

“So this initially leads you to get a lot of gas, but, in time, this might lead to another bacteria population in your gut developing, which could feed off that gas being produced, instead of firing it out,” says Mallard.

“You’ve got trillions of bacteria in your gut, particularly the colon, or large intestine. They play a very important role in your immune system, striking a balance between letting some stuff out and keeping the good stuff in.”

Health effects

“None,” says Dr Eamonn Quigley, gastroenterologist and co-director of the Underwood Center for Digestive Disorders at Houston Methodist Hospital, Texas.

“Excessive flatulence may reflect a change in the bacteria in the colon. Having a normal healthy bacterial population in the colon is essential to health.

“Bacteria have enzymes that can digest components of our diet that we cannot digest. In doing so they produce short chain fatty acids which help to sustain a healthy bowel and also gases that result in flatulence,” says Quigley.

Small quantities of volatile compounds.

In short, we fart because it’s a natural way of releasing gas from the gut. If we didn’t, we’d have serious health concerns.

“Flatulence is the result of gas generated in the colon by bacterial fermentation of carbohydrate, or protein, that has escaped absorption in the small intestine,” says Paula Mee, consultant dietitian and co-author of Your Middle Years: Love them, Live them, Own them.

Farts are a mix of hydrogen and carbon dioxide, with variable amounts of methane and nitrogen. Remarkably, all of these are odourless. So what causes such a stink?

“Odourless intestinal gases carry small quantities of volatile compounds such as cadaverine and putrescine, which are formed by the bacterial putrefaction of proteins,” says Mee.

“Hydrogen sulphide, which smells like rotten eggs, is also produced in the colon by sulphide-producing bacteria that break down sulphur-containing amino acids, as well as sulphite preservatives.”

Embarrassment

“Having been culturally conditioned from an early age, most of us try to contain our wind in company. Not to do so is seen as being downright rude. So it’s not so much the actual expulsion of wind that is the problem, it is what it represents: a lack of social competence and manners.”

As for why some of us fart more than others, Mee compares it to someone’s finger print: there are just so many compoundable factors. But we all let rip; only some of us do it more discreetly and consciously than others.

“Everyone is different, every microbiome is different and our dietary intake is different. But you have to add in stress as well, as we all experience it differently,” says Mee.

“Sometimes people with hypersensitive bowels, their negative or worrying thoughts can influence their bowel; it can go into spasm. It can transfer food rapidly through the digestive tract; so much so that the food isn’t properly digested and absorbed.”

And if you have excessive amounts of gas in your system, you probably don’t feel very well: you may notice some bloating, which can be uncomfortable, even painful.

“In some cases it’s a question of changing the diet but in others it could be a case of altering the microbiome through a course of probiotics,” says Mee.

“For example, if you have taken a number of courses of antibiotics, you probably will have obliterated a number of gut bacteria, which could lead to there being more flatulence than normal.”

Furthermore, deficiency in lactase (an enzyme located in the small intestines) can trigger flatulence, while holding off going to the toilet when you have a full rectum will also clock up your fart tally. “Better out than in, I always say,” Shrek wisely observed. But, remember, he was an ogre.

IBS

“When the symptoms interfere with your enjoyment of life, then they are worth investigating,” says Mee, adding that typical symptoms of IBS include abdominal discomfort, bloating or a change in bowel habits, such as repeated diarrhoea or constipation.

And, of course, flatulence, which can be fired by a combination of causes: intestinal sensitivity, rapid small bowel transit and the consumption of significant amounts of foods containing poorly absorbed, rapidly fermented carbohydrates; alias FODMAPs.

FODMAPs: not just hot air

Fermentable, oligo-, di-, mono-saccharides and polyols. The words alone are enough to give you the runs, but their acronym, FODMAPs, is somewhat more digestible.

FODMAPs are short-chain carbohydrates that the small intestine doesn’t absorb so well, to put it mildly. Originally identified by a research team at Monash University in Melbourne in 2005, their reduction in the diet has been proven to reduce flatulence in people with IBS and other gastrointestinal disorders.

But it’s far from a air-tight science, as factors such as the geography/location as well as the ethnicity of the consumer factor in.

There is a wealth of detailed information online on high- and low-FODMAP foods (start fodmapfriendly.com), but Mee cites excessive amounts of apple, blackberries, water melon, cabbage, cauliflower, broccoli, garlic, onion and leeks as A-listers in fart fermentation, not to mention peas, beans and lentils.

“At the first stage of reducing high-FODMAP foods you will be asked to cut out things like wheat, barley or rye and some dairy products, but not all,” says Mee.

High-FODMAP foods are cut out initially for six to eight weeks before gradually re-introducing them in groups to see how the body tolerates them.

The answer may be blowing in the wind.