Foods That Cause Gas and Bloating: The Gut Bacteria Behind It

The foods that cause bloating most often are beans and lentils, cabbage-family vegetables, onions, garlic and wheat, milk, high-fructose fruits and drinks, sugar-free sweets, fizzy drinks, fatty meals and salty processed food^[1][2]. Most of them bloat for one reason: they carry carbohydrates your small intestine cannot fully absorb, so gut bacteria in the colon ferment them and make gas^[3].

Below, the foods are grouped by how they bloat, with the doses that set off symptoms, the microbes doing the fermenting, and swaps that keep fiber in your diet. Bloating from food is usually harmless, but a few patterns need a doctor, so start with those.

Get medical help promptly if bloating comes with unexplained weight loss, a sudden change in your symptoms, persistent diarrhea or constipation, or abdominal pain that does not settle^[3]. These can signal a condition such as celiac disease, a bowel obstruction or, rarely, a cancer, and need a clinician rather than diet changes^[3][4].

Foods that cause bloating at a glance

Sources: NIDDK^[1], with the trials cited in each section below.

Why do certain foods cause bloating?

Most food-related bloating starts with fermentation. Carbohydrates that escape digestion in the small intestine reach the large intestine, where bacteria break them down and release gas^[3]. The main gases are carbon dioxide, hydrogen, methane and hydrogen sulfide^[5]. Swallowed air adds more, and fizzy drinks, gum and fast eating raise how much you swallow^[3].

Gas volume is only half the story. In an MRI study, 29 people with IBS and 29 healthy volunteers drank 40 g of inulin, fructose or glucose^[6]. Inulin raised colon gas and volume in both groups, yet bloating and pain were far more common in the IBS group^[6]. The authors concluded that a colon sensitive to stretching, rather than extra gas, drives many carbohydrate-related symptoms^[6].

That helps explain why one person eats a bowl of beans comfortably while another feels swollen for hours.

Not all bloating is gas. Only about half of people who feel bloated have a visibly larger belly^[3]. Constipation, SIBO and other conditions also cause it; our guide to bloating causes and relief covers the non-food reasons.

The 10 worst foods for bloating and excessive gas

These are the foods that make you fart and bloat most often, grouped by the reason they do it.

Beans, lentils and chickpeas

Legumes are rich in raffinose-family oligosaccharides, sugars that cause flatulence in humans^[7]. These carbohydrates reach the colon intact and feed gas-producing bacteria^[1].

The effect is smaller than many people expect. In three feeding studies where adults ate half a cup of beans a day for 8 to 12 weeks, fewer than half reported more gas in the first week from pinto or baked beans^[8]. Only 19% did with black-eyed peas, and 3 to 11% reported more gas even on the bean-free control diets^[8].

• Try first: smaller portions eaten daily, and black-eyed peas, which caused the least gas in those studies^[8].
• Enzyme option: in eight healthy volunteers eating 420 g of cooked beans, 1,200 GalU of the enzyme alpha-galactosidase cut breath hydrogen and flatulence^[9]. A pilot trial in 20 people with IBS found no benefit over placebo^[10].

Broccoli, cabbage, cauliflower and kale

NIDDK names cruciferous vegetables, including broccoli, cauliflower, collard greens and kale, among the vegetables most linked to excess gas^[1]. Cabbage and Brussels sprouts belong to the same family. Their carbohydrates are only partly digested before they reach colon bacteria^[1]. They are also high in fiber, and a sudden jump in fiber is a bloating trigger in its own right (see below).

Onions, garlic, leeks and wheat

These foods share one trigger: fructans, chains of fructose that the human small intestine does not digest^[11]. Among 60 vegetables measured, garlic, artichoke, shallots, leek bulb and onions held the most, at 1.2 to 17.4 g per 100 g^[11].

Wheat matters too, and gluten may be the wrong suspect. In a blinded crossover trial of 59 people who avoided gluten without having celiac disease, a 2.1 g dose of fructans raised bloating scores, while 5.7 g of gluten did not differ from placebo^[12]. If bread bloats you, rule out celiac disease with a blood test before cutting gluten, as the AGA advises^[4].

Fructans also show up as added fibers. Inulin and FOS (fructooligosaccharides), often listed as chicory root fiber, are fructans added to bars, cereals and drinks.

Milk, ice cream and soft dairy

Lactose bloats people whose small intestine makes too little lactase^[13]. Undigested lactose is fermented into hydrogen, carbon dioxide and methane^[13]. Whether you get symptoms depends on the dose, your lactase levels, your gut microbiome and how sensitive your gut is^[13].

Dose is the lever most people can use. Most people with lactose malabsorption tolerate at least 12 g of lactose, about 250 mL of milk^[13]. Our page on lactose intolerance covers testing and lactase supplements.

Source: Misselwitz et al., Gut, 2019^[13].

Apples, pears, watermelon and sweet drinks

The small intestine absorbs fructose only up to a point. In a dose-response study of 20 healthy adults, nobody malabsorbed 15 g of fructose and 10% malabsorbed 25 g without symptoms^[14]. At 50 g, 80% malabsorbed it and 55% had symptoms^[14].

In the MRI study, fructose pulled water into the small intestine and caused symptoms sooner than inulin did^[6]. NIDDK lists apples, peaches, pears and fruit juices, plus drinks made with high-fructose corn syrup, as common gas triggers^[1].

Sugar-free gum, candy and protein bars

Sugar alcohols, often lumped in with artificial sweeteners on "sugar-free" labels, end in "-ol": sorbitol, mannitol, xylitol, erythritol and maltitol^[1]. A systematic review of 79 studies found they cause dose-dependent gas, abdominal discomfort and loose stools in healthy people and in IBS^[15]. Malabsorption rises when several polyols are eaten together^[15].

Not all polyols act the same. In 64 young adults, a single 50 g dose of xylitol in water increased bloating and watery stools, while 20 g and 35 g of erythritol caused no significant symptoms^[16]. Chewing gum and hard candy add a second problem: you swallow more air^[3].

Sudden fiber increases and added inulin

Fiber is good for you, but more of it at once means more fermentation. In the DASH-Sodium feeding trial of 412 adults, a high-fiber diet (32 g a day) raised the risk of bloating by 41% compared with an 11 g diet^[2]. NIDDK also notes that too much fiber can increase gas^[1].

Isolated fibers have clear thresholds. In 26 healthy adults, up to 10 g a day of native inulin and 5 g of shorter-chain oligofructose were well tolerated; 10 g of oligofructose substantially increased gas and bloating^[17]. Check labels on prebiotic sodas and fiber bars, and use our high-fiber foods list to build up from whole foods gradually.

Fizzy drinks and swallowed air

Carbonated drinks add carbon dioxide directly, and NIDDK lists them alongside gum, straws and eating fast as ways to swallow more gas^[3]. Most of that carbon dioxide acts in the mouth, esophagus and stomach^[18]. A review found stomach discomfort appeared only when people drank more than 300 mL of a carbonated drink^[18].

Fatty and fried meals

Fat changes how gas moves rather than how much is made. When researchers infused gas into the small intestine, fat delivered at 1 kcal per minute made healthy volunteers retain 281 mL of gas, compared with 22 mL during a saline infusion^[19]. People with IBS retained gas even without fat and reacted to half that fat dose^[19]. NIDDK likewise lists high-fat foods as a bloating trigger^[1].

Salty and processed foods

Sodium is a bloating trigger with randomized evidence behind it. In the same DASH-Sodium trial, the highest sodium level raised bloating risk by 27% compared with the lowest, on both the high- and low-fiber diets^[2]. The researchers suggested that cutting sodium may offset some of the bloating from a high-fiber diet, but they could not explain the mechanism^[2].

Which gut bacteria turn food into gas?

Fermentation is a team effort. Firmicutes and Bacteroidetes make up more than 85% of adult gut bacteria, and culture studies suggest Firmicutes release most of the free hydrogen^[20]. More than 70% of 343 sequenced gut genomes carried genes for hydrogen-making enzymes^[20].

Other microbes then use up that hydrogen, and they decide what kind of gas you end up with^[21]:

• Methanogens make methane. Methanobrevibacter smithii is the most abundant, and Methanosphaera stadtmanae is also common^[20]. Methane levels are higher in people with constipation or IBS^[21].
• Sulfate-reducing bacteria, mostly Desulfovibrio species such as Desulfovibrio piger, make hydrogen sulfide^[20]. That gas is the one most closely tied to flatus odor^[22]; our post on why farts smell so bad goes deeper.
• Acetogens turn hydrogen into acetate, one of the short-chain fatty acids^[20].

These patterns line up with symptoms. In a Cedars-Sinai study of people with IBS, constipation-predominant IBS was tied to higher breath methane and more M. smithii in stool, while diarrhea-predominant IBS was tied to more hydrogen sulfide and more Desulfovibrio and Fusobacterium^[23]. Breath tests that measure hydrogen and methane are how clinicians check for lactose intolerance and SIBO^[21].

The same fermentation has an upside. Moderate doses of polyols raised bifidobacteria in healthy people^[15], and the fibers your own enzymes cannot digest are what gut microbes turn into short-chain fatty acids such as acetate, propionate and butyrate^[24]. The goal is a dose your gut tolerates, not zero fermentable food.

How do you find your trigger foods?

Start with a record, not a long elimination list. NIDDK suggests a food and symptom diary so a doctor or dietitian can spot patterns^[1].

1. Log for one to two weeks. Write down what you ate, portion size, timing, and when bloating started. Fructose symptoms tend to start sooner than fructan symptoms^[6].
2. Change habits first. Eat slowly and sitting down, choose smaller, more frequent meals, and cut back on gum, straws and fizzy drinks^[1].
3. Test one suspect at a time. Reduce portions of a single group, such as lactose or sugar alcohols, rather than several at once.
4. Consider a supervised low-FODMAP trial for IBS. A meta-analysis of 12 studies found the low-FODMAP diet reduced IBS symptom severity compared with control diets^[25]. The AGA advises doing it with a GI dietitian^[4], and NIDDK frames it as a trial of a few weeks^[1]. Our SIBO diet guide explains how it differs from SIBO-focused plans.

Probiotics are a common next step, but the AGA's 2023 expert review advises against using them to treat bloating and distention^[4]. We weigh the strain-level trials in probiotics for bloating. If you suspect an intolerance beyond lactose, our page on food sensitivities explains what testing can and cannot show.

What to eat instead to calm a gassy stomach

Swaps work better than cutting whole food groups, because most trigger foods also feed beneficial microbes. Each swap below links to the evidence behind it.

If one food reliably sets you off, keeping it at a smaller portion is often enough. Trapped gas that is already causing pain has its own fixes; see our gas pain guide.

When to see a doctor about bloating

Occasional bloating after a big or bean-heavy meal is normal. NIDDK advises talking with a doctor if^[3]:

• gas or bloating bothers you or disrupts daily life;
• your symptoms change suddenly;
• bloating comes with abdominal pain, constipation, diarrhea or weight loss.

Extreme or constant bloating that does not follow meals deserves a check-up. Conditions behind it include IBS, lactose or fructose intolerance, SIBO, celiac disease, constipation, gastroparesis and, less often, a blockage from colorectal, ovarian or stomach cancer^[3]. The AGA recommends imaging or endoscopy when there are alarm features, recent worsening or an abnormal exam, and a celiac blood test for people with bloating^[4].

This article is for general educational purposes and is not medical advice. Food triggers vary from person to person, and a food diary or elimination trial does not replace testing for celiac disease, lactose intolerance or other conditions. Talk to a qualified healthcare professional before making major diet changes, particularly if you are pregnant, immunocompromised, taking prescription medication, or managing a diagnosed condition.