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To fart is human. On a normal day, people break wind on an average of 14 times, discharging half a liter to more than 2 liters of gas. And although 99% of the gas is free of odor but sometimes farts can be downright nasty. According to Patricia Raymond, MD, a Virginia Beach-based gastroenterologist, usually the silent farts are the smelliest ones and that is due to the bacterial fermentation process in the colon.

So if the person releases a wicked smelling gas, it is usually something they ate, which is not essentially a bad thing. Gas is a normal and healthy sign of digestion, and while the smell may be an issue especially in a social situation, it merely shows that the person has fed nutritious, fiber-rich, plant-based foods to their gut. However, there can be situations where a bad odor may signal a much grim health issue that would require visiting a GI doctor.

Reasons of Smelly Farts

So here are eight reasons why the gas you pass can sometimes be offensive.

Bugs in the guts

During digestion, the bacteria present in the gut begin producing high-sulfur compounds such as Hydrogen Sulfide that produce smell in the gas, as according to Dr. Raymond. The foods we usually consume can affect the inhabitants of bacteria that reside in the colon, which consequently affect our farts. This is explained by Frederick Gandolfo, MD, who is also a gastroenterologist at Precision Digestive Care in New York. He says that different people have different composition of flora present in gut region that results in production of smellier gas.

Sulfur-rich foods

Foods that contain sulfur in high amount can also give farts stench of rotten eggs. Such foods include cruciferous veggies like Brussels, broccoli, cauliflower, cabbage and sprouts. Other foods rich in sulfur include onions, legumes, garlic, wine, beer, dried nuts, cheddar cheese, dried fruit and nuts. Even animal proteins are high in sulfur which may be an issue.

In an experiment that involved seven healthy individuals, an Australian research team found that a sulfur-rich component found in protein complex causes increase in stinky hydrogen sulfide emissions by seven fold. The lead researcher speculates that it could explain why bodybuilders, who tend to eat large amount of protein, are notorious for smelly farts, the lead researcher speculated.

Lactose intolerant

Dairy products such as milk, cheese and ice cream can also cause stinking, and rightly so. Between 30 to 50 million Americans have deficiency of lactase enzyme required lactose digestion, which is a natural sugar usually found in dairy products.

In such deficiency, lactose goes through the intestines without getting digested, and travels down to the colon where the bacteria get to work. Folks may also be intolerant to and pass smelly farts from other sugars such as table sugar and corn syrup etc.


Beans are a rich source of protein, minerals, vitamins and antioxidants. But they have a bad reputation for producing unusually more fart. This is because beans are full of RFOs or Raffinose Family Oligosaccharides, which is a sugar complex responsible for bloating and may also cause gas after a meal full of beans. Same goes with lentils and cruciferous veggies.

Soaking dried beans in water usually helps drain out RFOs while preserving all the nutrition. Taking an enzyme-based digestion aids such as Beano also helps reduce the condition.

Sugar Alcohol

Sugar alcohol can be found in sugar-free candies, diet drinks and even in chewing gum. These sweeteners do not get completely digested by the body so they travel through the colon contribute to stinking gas.

Keeping a food diary is a good way to determine if sugar alcohols are causing those smelly farts. As Dr. Raymond recalls a visit from a former female patient who had smelly gas problem but curiously on weekdays only, later found out that a big sugar-free candy jar at her workplace was the reason, as she would grab a few daily.


Bagels, rice, and pasta are usually low on fiber and not really a cause of producing gas. But consuming large amounts of the low-fiber content may cause difficulty in moving bowels and that’s when farts get funky. During constipation, poop stays in the colon for longer duration and the bacteria cause large amount of gas.

It is recommended to drink plenty of water, exercise regularly and eat high-fiber foods in order to keep from getting backed up.


Certain medication and supplements can play a role in turning farts foul. The reasons they cause smelly farts vary in type and amount, and also vary from one person to the other. So every person will need to weigh the benefits and risks of the offending agent.

Orlistat is a common weight loss medication which causes oily gas discharge. Iron supplements are also known to give gassy and bloating feeling. High-fiber supplements also cause gas and a diabetes drug called Metformin may also give constant gas.

Infection or Disease

A smelly fart by itself is usually harmless but it may need to be checked out if one also has other signs and symptoms. It is good to talk to a doctor in case of persistent diarrhea, blood in the stool, fever, bowel problem, weight loss along with stinky farts. Any change in bowel behavior or abdominal pain that persists after passing gas or stool could be sign of trouble.

It is important to rule out or treat other conditions for causing smelly farts such as bowel disruption, bowel inflammation, celiac disease, colon cancer and C. difficile. As such there doesn’t exist any medical guideline identifying regularity or capacity of flatulence, so one is probably the best person to evaluate their own symptoms.

When to see a doctor?

See a doctor in case flatulence is particularly bothersome and concerning such as frequent passing of smelly gas. One should also consult a doctor when experiencing additional symptoms such as:

  • persistent abdominal pain and bloating
  • recurring episodes of diarrhoea or constipation
  • unexplained weight loss
  • bowel incontinence
  • blood in your stools (faeces)
  • signs of an infection, such as a high temperature, vomiting, chills, joint pain and muscle pain

Such symptoms could indicate a more serious health issue and may require further examination to look for an infection.

How to prevent Smelly Farts?

Flatulence is natural and integral to clear out waste and gas from the body. There are some things one can do to prevent smelly farts:

  • Eating slowly and in smaller portions encourages healthy digestion and reduces gas discharge.
  • Drinking plenty of water helps in moving waste through the body more smoothly.
  • Including foods with probiotics such as yogurt in the diet also helps to restore good bacteria in the gut and improves digestion.
  • Avoid carbonated drinks that can produce gas, including beer and soda.
  • Also avoid foods that cause smelly gas.


One of the most common ways to prevent smelly farts include identifying the triggers in a food diary, avoiding foods that result in foul smell and also taking foods that are known to help in preventing smelly flatulence. Though the above mentioned ways could help in some way, be sure to consult a doctor in case these remedies do not provide relief and the smelly farts persist. Some digestive disorders such as Irritable bowel syndrome or IBS can be linked to smelly gas, which requires medical treatments. And drink plenty of water.

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