Trust your gut feeling (literally).
Reviewed by Dietitian Katey Davidson, M.Sc.FN, RD, CPT
Key Points
- Excessive or smelly farts can sometimes point to an underlying digestive issue.
- Impaired digestion, carbohydrate malabsorption and dysbiosis can contribute to smelly gas.
- See a health care professional if gas comes with other persistent symptoms.
Just like everybody poops, everyone also farts. But not all farts are created equal when it comes to their odor, sound, frequency or what they may indicate about your digestive health.
“Typically, odorless farts are a normal part of digestion,” says Rucha Shah, MDnoting that occasional gas is a sign of a healthy, functioning digestive system. On the other hand, chronic, excessive or particularly smelly gas—especially when accompanied by other gastrointestinal symptoms—may be a sign that something is going on with your digestive health.
We spoke with gut-health experts about digestive health issues that may cause excessive, persistent or foul-smelling gas, plus the signs that mean it may be time to see a health care professional.
1. Impaired Digestion
Impaired digestion is a broad term used when the digestive process isn’t working properly. This can happen when the body doesn’t produce enough stomach acid, digestive enzymes or bile, which help break down food and support nutrient absorption.
When digestion or absorption is impaired, some food components may reach the colon without being fully digested or absorbed. There, gut bacteria can ferment them and produce gas.
“Conditions that prevent you from breaking down foods or absorbing certain nutrients can result in excessive gas production because undigested food components often get fermented by the bacteria in your colon,” explains Sarah Glinski, RD. This fermentation can contribute to smelly or excessive gas, bloating and abdominal discomfort.
People who have had their gallbladder removed or who have certain pancreatic or gastrointestinal conditions may be at greater risk of impaired digestion or nutrient absorption.
2. Carbohydrate Malabsorption
“Carbohydrate malabsorption is when you have trouble absorbing certain carbohydrates [such as lactose, fructose, FODMAPs or other sugars]which leads to excessive gas,” explains Supriya Rao, M.D., DABOM, DABLM. When these undigested carbohydrates reach the colon, bacteria ferment them. Rao notes that the microbial fermentation is the primary underlying culprit of bloating and foul-smelling farts.
Latha Alaparthi, MDadds that certain nondigestible dietary ingredients, such as sugar alcohols and some artificial sweeteners, can also trigger intestinal fermentation and subsequent gas symptoms for some people.
If you suspect you have carbohydrate malabsorption, work with a registered dietitian who specializes in gut health and keep a detailed food-symptom journal to help identify patterns and pinpoint food-symptom triggers. In some cases, consulting a gastroenterologist may be needed if an underlying condition is suspected, such as small intestinal bacterial overgrowth (SIBO), inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) or celiac disease.
Shah points out that not everyone who has carbohydrate malabsorption will experience noticeable symptoms. “People with a more sensitive gut, like those with IBS, tend to feel the bloating and [gas] more intensely.”
3. Dysbiosis
A healthy and diverse gut microbiome—the community of microbes living mostly in your large intestine—plays an important role in digestion, nutrient production and maintaining the gut lining. When the balance of microbes is disrupted, changes in fermentation can affect the amount and type of gas produced.
This type of microbial imbalance is referred to as dysbiosis, an unhealthy imbalance in which healthy microbes are reduced, leaving a window of opportunity for potentially harmful microbes to overgrow and affect digestive function.
“Dysbiosis can result in increased gas production, stronger odors, bloating and changes in bowel habits due to altered fermentation patterns,” explains Ashley Oswald, RDN, LD, IFNCP, CLT. “This type of imbalance can lead to the breakdown of undigested protein in the large intestine, which produces compounds like ammonia and hydrogen sulfide,” Glinski adds, noting it can lead to excess gas and foul-smelling farts if left unchecked.
Oswald highlights common underlying factors that can contribute to dysbiosis, including antibiotic use, a diet low in dietary fiber and plant diversity, chronic stress, gut infections, poor sleep, certain medications, chronic health conditions and inflammatory bowel conditions.
4. Small Intestinal Bacterial Overgrowth (SIBO)
Small intestinal bacterial overgrowth (SIBO) is a specific type of gut dysbiosis in which there is an abnormal increase in bacteria in the small intestine. When gas is accompanied by chronic bloating, particularly within about 30 minutes up to three hours after eating, this may be a sign of SIBO, says Oswald.
“In SIBO, bacteria that normally reside primarily in the large intestine migrate to the small intestine and ferment carbohydrates before they can be absorbed,” Oswald explains, pointing out that the microbial fermentation seen in SIBO produces hydrogen, methane and other gases.
The type of gas produced may also influence the odor. “If you have hydrogen sulfide-dominant SIBO, your farts may smell like rotten eggs,” Glinski shares. “Excess hydrogen gas in some can cause the smelliness,” Alaparthi adds.
It’s important to note that while SIBO may contribute to gas and bloating, it can also occur alongside underlying digestive conditions or motility problems. Because its symptoms overlap with several other gastrointestinal conditions, proper evaluation is important rather than assuming SIBO is the cause of excessive gas.
5. Intestinal Methanogen Overgrowth (IMO)
Intestinal methanogen overgrowth (IMO) is another form of dysbiosis characterized by an overgrowth of methane-producing microbes—specifically Methanobrevibacter smithii—in the intestinal tract, says Shah. “These archaea consume hydrogen produced by other gut microbes and convert it into methane gas,” she explains.
IMO is differentiated from SIBO in that it is caused by archaea (versus bacteria), Shah and Oswald point out. Unlike SIBO, which is limited to the small intestine, IMO can occur throughout the intestinal tract. IMO is associated with chronic constipation, as methane can slow intestinal transit. “Slowed motility allows for further overgrowth in the gut microbiome and increased bloating that may worsen throughout the day along with [gas],” Oswald adds.
If persistent gas is accompanied by chronic constipation, IMO may be one possible explanation—but testing and evaluation by a health care professional are needed to determine the underlying cause.
When to See a Health Care Professional
“It’s important to take persistent digestive symptoms seriously, even if it feels embarrassing to bring it up with your doctor,” says Glinski. If your gas seems to be more frequent or noticeably more odorous than usual, particularly if the change is persistent or accompanied by other symptoms, it’s worth discussing with a health care professional.
Experts recommend talking with your health care team and doing some detective work to figure out what could be causing the gas, especially if you also experience any of the following:
- Foul-Smelling or Excessive Gas. Oswald advises that when you’re farting more than your typical amount or notice foul-smelling odor, it may indicate that something significant is affecting your digestive function or gut microbiome.
- Persistent Bloating. Bloating that doesn’t improve with dietary changes can occur with SIBO, celiac disease or other gastrointestinal disorders. Shah points out that in women over the age of 50, persistent bloating can also sometimes be an early sign of ovarian cancer.
- Blood in Your Stool. All experts agree that seeing blood in your stool is a major red flag. Notify your health care provider right away if you ever notice any red or tar-colored stools, which can indicate gastrointestinal bleeding, to rule out serious conditions.
- Severe Abdominal Pain. Severe or worsening abdominal pain could be a sign of a medical condition and should not go left unchecked.
- Unintentional Weight Loss. Unintentional weight loss can accompany gastrointestinal symptoms in conditions including bowel cancer, which can sometimes be mistaken for IBS during its earlier stages, and should not be overlooked.
- Chronic Diarrhea or Constipation. “If you have changes in bowel habits, persistent diarrhea or constipation, please let your provider know,” Rao advises.
- Vomiting. Persistent or unexplained vomiting alongside gastrointestinal symptoms warrants further evaluation by a health care professional.
Our Expert Take
Gas is a normal part of digestion, but a persistent change in the frequency, amount or odor of your farts—especially when accompanied by other digestive symptoms—may be worth investigating. Potential causes range from carbohydrate malabsorption and impaired digestion to changes in the gut microbiome and conditions such as SIBO or IMO.
“Appropriate testing can then be conducted to help identify the underlying cause and guide individualized treatment,” Oswald says. If your farts seem noticeably different from your usual, don’t be embarrassed to bring it up with your health care provider. Identifying the underlying cause can help you get the right treatment, and ultimately, feel better.