What causes bloating in the stomach?
Gas
Gas is a natural byproduct of digestion, but too much intestinal gas means your digestion is gone awry. While you can ingest gasses by swallowing air or drinking carbonated beverages, these gasses mostly escape through belching before they reach your intestines. Gasses in your intestines are mostly produced by gut bacteria digesting carbohydrates, in a process called fermentation.
If there’s too much fermentation going on, it’s because too many carbohydrates weren’t naturally absorbed earlier in the digestive process, before reaching those gut bacteria. That could be for several reasons. Maybe you just ate too much too fast for proper digestion. Or you might have a specific food intolerance or gastrointestinal (GI) disease. Some possible causes include:
- Carbohydrate malabsorption. Many people have difficulties digesting particular carbohydrates (sugars). Some common culprits include lactose, fructose and the carbs in wheat and beans. You may have an intolerance, or you may just have general difficulties that cause your body to struggle more with tougher carbs. A nutritionist or GI specialist can help you isolate your dietary sensitivities.
- Small intestinal bacterial overgrowth (SIBO). This occurs when gut bacteria from the colon overflow into the small intestine. The overgrowth of these bacteria can also overwhelm other bacteria that are meant to balance them. Some bacteria actually absorb the gasses produced by others, but too many of one kind and not enough of another kind can throw this balance off.
- Functional digestive disorders. IBS and functional dyspepsia are diagnosed when your body struggles more with digestion for unexplained reasons. Symptoms often include gas and bloating after eating. Keep an eye out for classic alarm symptoms such as diarrhea or constipation, nausea, vomiting, fever, bleeding, anemia, and unintentional weight loss.
- Visceral hypersensitivity. Some people feel like they’re gassy and bloated even when their volume of gas is normal. This condition often correlates with IBS and other disorders involving the gut-to-brain neural pathways. Some people even develop a muscular hyper-reaction to make more room in the abdominal cavity for gas (abdominophrenic dyssynergia). Their abdominal muscles relax and protrude outward in the presence of gas, even when the actual volume is normal.
Digestive Contents
These can include solids, liquids, and gas. Digestive contents can build up in your digestive system when there is a backup or restriction in your digestive tract or when the muscles that move digestive contents along are somehow impaired. Any build-up of digestive contents along the digestive tract will leave less room for normal amounts of gas to process through. It also leaves less room for other things in your abdomen, including circulatory fluids and fat, making everything feel tighter. Causes of build-up can include:
- Constipation. You may have occasional constipation due to diet or lifestyle factors, or you may have chronic constipation due to an underlying condition. Backed-up poop in your colon causes recently-digested food to stay longer in the intestines, waiting to descend. Everything expands to contain the extra volume, leading to bloat.
- Bowel obstructions. When it isn’t backed-up poop obstructing your bowels, it could be something more serious. Both your large and small bowels can become blocked by tumors, scar tissue, strictures, stenosis, or hernias. Inflammatory diseases such as Crohn’s disease and diverticulosis can damage parts of your small bowels, creating strictures that narrow the passage of digestive contents.
- Motility disorders can cause constipation, or they can simply cause everything to move more slowly through your digestive tract. These are usually disorders of the muscles and nerves that sense digestive contents in the digestive tract. Examples include intestinal pseudo-obstruction, a condition that mimics the effects of an obstruction when there is none, gastroparesis, partial paralysis of the stomach muscles, and pelvic floor dysfunction.
- Recent weight gain. Weight gained within the last year or so tends to go to your belly first. If you’ve gained ten pounds or more, it’s probably impacting your abdominal volume. This means less room for normal digestive processes, so that even a normal meal may cause you to feel abnormally bloated during digestion. Sometimes weight gain also involves water retention, which can make you feel bloated with fluids in your stomach and elsewhere.
Hormones
Maybe you’ve noticed that your stomach bloating follows a different cycle — not so much your digestive cycle, but your menstrual cycle. If so, you’re not alone. As many as 3 in 4 women say they experience abdominal bloating before and during their menstrual periods. Bloating is also a common complaint during the hormone fluctuations of perimenopause. Female hormones deserve a special mention when it comes to stomach bloating because they can affect bloating from many angles — fluids, gas, digestive back-up — and also your sensitivity to those things.
First, estrogen causes water retention. When estrogen spikes and progesterone drops, you'll notice bloating from fluids. This, in addition to the increased volume of your uterus just before menstruation, can give you a bloated stomach. But hormones also interact with your digestive system. Estrogen and progesterone can each cause intestinal gas by either slowing or speeding your motility. Estrogen receptors in your GI tract also affect your visceral sensitivity — what makes you feel bloated.
Other Causes
Bloating that comes and goes is usually digestive, hormonal or both. These causes can also make you feel generally sick and tired. As long as your symptoms eventually go away, they probably aren't serious. But if your bloated stomach doesn’t go away or gets worse, or if you have other symptoms of serious illness, such as fever or vomiting, you should seek medical attention to rule out other medical causes. These may include:
- Ascites. This is a gradual build-up of fluid in your abdominal cavity. It’s usually caused by liver disease, and sometimes by kidney failure or heart failure.
- Pancreatic insufficiency. This is a kind of pancreatic dysfunction in which your pancreas can no longer make enough digestive enzymes to serve its function in the digestive process.
- Inflammation of the stomach (gastritis) or the intestines (enteritis). This is usually caused by a bacterial infection (commonly, H. pylori infection) or by drinking too much alcohol. It can also be related to peptic ulcers.
- Cancer (ovarian, uterine, colon, pancreatic, stomach or mesenteric). Yearly check-ups with your primary care physician are important to screen for cancer.
