Gas is one of the commonest reasons people come to a gastroenterology clinic, and one of the most embarrassing to talk about. It should not be. A healthy gut produces somewhere between half a litre and two litres of gas a day, and passing wind ten to twenty times a day is normal. The question is not how to stop gas altogether - that is impossible - but why some people have much more of it, or find it much more uncomfortable, and what actually helps.
Where gas comes from
There are two sources. The first is swallowed air: every time you swallow, a little air goes down with it, and more goes down when you eat quickly, talk while eating, chew gum, drink through a straw, drink fizzy drinks or smoke. Swallowed air is mostly burped back up; what continues down is passed as wind.
The second source is fermentation. Carbohydrates that the small intestine cannot fully digest - fibre, certain sugars, resistant starch - reach the colon, where bacteria ferment them and release hydrogen, carbon dioxide and, in some people, methane. This is a normal and even healthy process; the same fermentation produces the fatty acids that nourish the colon lining. But the amount and the smell depend on what is fermented, and the discomfort depends on how sensitive your gut is to being stretched.
Foods that produce more gas
- Beans and dals - rajma, chana, chole, whole moong, urad - contain raffinose-family sugars that we cannot digest but bacteria can.
- Cruciferous vegetables - cabbage, cauliflower, broccoli, radish.
- Onion and garlic, and wheat in large quantities, because of fructans.
- Milk and milk products in people with lactose intolerance, which is common in India - the lactose reaches the colon undigested.
- Sugar-free sweets and gums containing sorbitol, xylitol or mannitol.
- Fruit high in fructose - mango, apple, pear, watermelon - in some people.
- Fizzy drinks and beer, which deliver gas directly.
Notice that most of this list is healthy food. The aim is not to avoid beans and vegetables for life but to identify which ones affect you, and to prepare them in ways that reduce the effect.
Practical ways to reduce gas
- Soak and rinse pulses for 8-12 hours, discard the water, and cook thoroughly; pressure cooking helps. Sprouting also reduces the gas-forming sugars.
- Use the traditional digestive spices - hing (asafoetida), jeera, ajwain, saunf and ginger - in dals and vegetables. There is a reason Gujarati cooking pairs them with pulses.
- Eat slowly and sit down to eat. Chew well, do not talk with a full mouth, and avoid drinking large volumes with meals.
- Cut fizzy drinks, chewing gum and straws.
- Test lactose. Stop milk, curd and paneer for two weeks; if symptoms clearly improve, reintroduce curd first (it is better tolerated) and use lactose-free milk.
- Increase fibre slowly. A sudden jump in fibre is a classic cause of a bloated week.
- Walk after meals. Ten to fifteen minutes of walking moves gas along and eases bloating.
- Treat constipation. Stool that sits in the colon ferments for longer; regular bowel movements reduce both gas and its smell.
Over-the-counter simethicone and activated charcoal are safe and help some people with bloating, but the evidence is modest. Probiotics help a minority; if you try one, give it four weeks and stop if there is no change.
When gas is not just gas
Gas and bloating are usually harmless. Sometimes they are the way a real condition first shows itself - irritable bowel syndrome, small-intestinal bacterial overgrowth, coeliac disease, lactose intolerance, slow stomach emptying, or, less often, a blockage or a growth. See a gastroenterologist if gas or bloating comes with:
- Weight loss without trying, or loss of appetite
- Blood in the stool, black stools, or persistent diarrhoea
- Abdominal pain that wakes you at night or keeps getting worse
- Bloating that is constant rather than related to meals, or a visibly distended abdomen
- Vomiting, or inability to pass wind or stool (an emergency)
- New symptoms after the age of 50, or a family history of bowel cancer or coeliac disease
Assessment is usually simple: a careful history and examination, blood tests, sometimes a breath test for lactose intolerance or bacterial overgrowth, and endoscopy or motility studies when needed. Read more about stomach pain and indigestion and IBS.
