Bring up farts and suddenly the most mature adult seems to morph back into an awkward teenager. However, passing gas is not only completely normal but an important indicator of your digestive health, which has a significant impact on your overall well-being.
“The digestive system is the body’s main way to take in and absorb nutrients, which is essential to sustain life, but it’s so much more than that,” says gastroenterologist Dr Shilpa Ravella. “As a barrier from the outside world, it’s also one of the body’s main defences against disease and the home of the trillions of bacteria that play an essential role in health.”
The average person will fart about 10 to 30 times a day, says gastroenterologist Dr Andrew Boxer, and there are many reasons why this might have a foul odour. However, it often does not mean much if somebody has very foul smelling gas, he adds. “Usually, this is not a sign of poor health.”
Still, particularly foul-smelling (or constant) farts can indicate some sort of issues in the GI tract. Here, digestion experts share common causes of unusually smelly farts and when to see your doctor about it.
Causes of smelly farts
1. Sulphur-heavy foods
According to Dr Ravella, super-smelly gas is often the result of eating foods rich in sulphur, which the digestive system breaks down into stinky compounds called sulphides. Two high-sulphur foods we eat a lot of: meat and eggs. Ever had gas that smells like rotten eggs? Yeah, that’s from a nasty by-product called hydrogen sulphide.
Other foods that can lead to sulphide-related smelly farts include garlic, sulphite-containing wines, and dried fruits preserved with sulphur dioxide, says dietitian Marta Ferraz Valles.
FODMAPs, a family of short-chain carbohydrates found in all sorts of foods, can also cause digestive issues that stink up your gas. “FODMAPs are poorly absorbed in the small intestine, osmotically active (meaning they increase intestinal water content), and are quickly fermented by gut bacteria,” says Dr Ravella. For sensitive people, this can lead to more (and worse-smelling) gas.
Unfortunately for sensitive stomachs, all sorts of foods contain FODMAPs, including certain fruits (like watermelon and mangoes) and vegetables (like broccoli and Brussels sprouts), high-fibre grains, onions, dairy, and the list goes on, says Dr Ravella.
You’ll also find FODMAPs like sugar alcohols (think sorbitol) and fructose in lots of processed foods, Ferraz Valles adds.
2. High-fibre foods
Fibre, the indigestible parts of the plants we eat, is an incredibly important part of our diet. In addition to supporting a healthy digestive system (and regular bowel movements), it also makes us feel satiated after eating, helps stabilise our blood sugar, lowers cholesterol, makes maintaining a healthy weight easier, and helps us live longer, reports the Mayo Clinic.
But many of us don’t regularly eat enough fibre, and suddenly loading up on it can cause some digestive upset and increased flatulence, says Ferraz Valles. (Beans and legumes, for example, are a common culprit here.)
Often, it takes a few weeks for the digestive system to adjust to increased fibre intake, which is why Ferraz Valles recommends gradually increasing intake to the recommended amount (25 grams a day for women and 30 grams a day for men) and drinking plenty of water alongside fibrous foods like oats, apples, lentils, and berries.
3. Medications
Sad but true: all sorts of medications and dietary supplements, even those meant to ease stomach issues, can affect your farts, says Ferraz Valles.
NSAIDs (like ibuprofen), antacids, diarrhoea medications, chemotherapy drugs, multivitamins, and fibre supplements can cause changes in flatulence frequency and odour, she says. It’s inconvenient, yes, but not necessarily anything to be concerned about.
4. Lactose intolerance
Lactose, a natural sugar found in dairy products, is famously difficult for many adults to digest. “One of the most common reasons people may suffer from excessive gas is lactose intolerance,” says Ferraz Valles.
Fructose or lactose intolerance can result in smelly gas as well, explains Dr Boxer. “If a patient lacks the enzyme to properly break down these sugars, they can pass through your small intestines into your colon where bacteria will digest them releasing gas.”
Since different dairy products contain different amounts of lactose (milk contains more than hard cheese, for example), people may notice worse symptoms after eating different types of dairy, says the American National Institutes of Health. However, abdominal pain, bloating, nausea, and lots of smelly farts 30 minutes to two hours after eating dairy indicate lactose intolerance.
5. Gluten sensitivity or coeliac disease
Gluten, the always-controversial protein found in grains like wheat, barley, and rye, can also contribute to problematic flatulence. “People who have coeliac disease or non-coeliac gluten sensitivities may experience excessive gas when consuming gluten,” says Ferraz Valles. In both cases, consuming gluten can also contribute to a slew of digestive issues, as well as nutrient deficiencies and fatigue, according to Coeliac Australia.
However, while genetic coeliac disease can be identified through blood testing, identifying a gluten sensitivity or intolerance typically just involves observing changes in symptoms after removing gluten from the diet (which should be done under the supervision of a dietitian or doctor).
6. Gut bacteria imbalance
“Bacterial imbalances can certainly cause excessive and foul-smelling gas,” says Dr Ravella. People with low bacterial diversity in their gut (which can be caused by frequent, excessive antibiotic use or a diet low in fibre and high in animal products) often face this issue, Dr Ravella says.
Another common culprit, though, is small intestinal bacterial overgrowth, also known as SIBO, she says. SIBO occurs when excess bacteria builds up in the small intestine, which can affect nutrient absorption and cause all sorts of digestive symptoms (including an uptick in flatulence).
7. Constipation (and maybe IBS)
Irritable bowel syndrome (IBS), a condition in which dysfunction in the large intestine causes digestive issues like bloating and abdominal pain, and bouts of diarrhoea and constipation, is yet another common culprit behind particularly smelly farts, according to the Mayo Clinic.
Constipation alone can lead to smelly gas as well, says Dr Boxer. “If stool sits in the GI tract for a long time, bacteria can increase their time of digestion and release gas.”
Though frequent gas alone is not enough to diagnose IBS, changes in gas odour and production are common factors, says Dr Ravella. Often, managing IBS involves making healthy diet and lifestyle changes, as well as addressing stress.
How to prevent smelly farts
There are a few ways to prevent smelly gas, says Dr Boxer. “I find the most common is to treat constipation, since foul smelling gas is one of the most common signs of constipation.” Taking over-the-counter laxatives can be a simple, short term home remedy for constipation.
Going on a low FODMAP diet is also a scientifically proven way to decrease gas and bloating, says Dr Boxer. “This will also decrease flatulence.”
Dr Boxer also adds that sometimes probiotics can also be helpful in preventing smelly gas.
When to see your doctor about smelly farts
Though gas varies from person to person, regularly stinky farts, when in combination with certain other symptoms, do warrant a trip to the doctor, as they can indicate serious conditions, like colon cancer. According to Dr Ravella, the following are cause for concern:
- Bloody poo
- Unexplained weight loss
- Fever
- Severe abdominal pain
- Vomiting
However, even consistently smelly farts accompanied by more minor digestive upset (like bloating) can indicate issues like food sensitivities and bacterial imbalances, Dr Ravella says. In these cases, a registered dietitian can help you evaluate and modify your diet to ease your symptoms.
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