We all do it— burp, bloat, or let one slip— but have you ever stopped to wonder what is really causing all that gas? From the beans you ate last night to the broccoli on your plate, your gut has a story to tell. And sometimes, it is louder than we would like.
Dr Amos Mwasamwaja, a consultant gastroenterologist at Aga Khan University Hospital, says legumes cause more gas because they have a type of starch that is not undigested called raffinose. It is found in beans, lentils, chickpeas, broccoli, Brussels sprouts, cabbage, wheat, and asparagus.
But Dr Mwasamwaja says that gas in our digestive system primarily originates from the air we swallow. When we eat, we swallow a lot of gas. But there is also a mechanism too. For most people, for every bowl of food you take, usually there is some amount of air that goes in.
"But most of this air returns just within the food before it enters the stomach. So that's why we expect few people to have what we call supergastric belching. This means the expulsion of gas from the oesophagus rather than the stomach. This is caused when air is swallowed but does not reach the stomach."
What about the burping and the belching? "Expelling of gas when it is too much, meaning that someone has a lot of what we call super gastric gas. This is gas trapped above the stomach, typically in the oesophagus or lower throat."
Dr Mwasamwaja says that the supergastric gas is caused by carbonated drinks, eating or drinking quickly, excessive swallowing of air, medical conditions, or even anxiety/stress.
What are the types of gas we swallow?
Dr Mwasamwaja says the most common is just air. And in air, you have oxygen, nitrogen, and hydrogen. So mostly, the swallowed air is oxygen and nitrogen.
For luminal gas (gas present within the lumen of the gastrointestinal tract, which includes the stomach, small intestine, and large intestine), there are majorly three gases: carbon dioxide, hydrogen, and methane.
"Carbon dioxide is derived from the digestion of fats and proteins. Hydrogen is produced from bacteria's fermentation of intraluminal substances. Methane is just like hydrogen, an exclusive by-product of bacterial metabolism."
But why does someone shoot and it smells so bad? "There is what we call hydrogen sulfide, and it is caused by eating food rich in sulphur compounds, like some vegetables such as broccoli, cabbage, onions, garlic, and Brussels sprouts. Also, undigested proteins and fibres, and even some sulphate-reducing bacteria. Conditions like irritable bowel syndrome and bacteria in the small intestine that produce excessive gas."
How does one have excess gas swallowing?
You can swallow if you eat too fast, chewing and eating while talking. Dr Mwasamwaja also adds those who breathe from the mouth either when jogging or snoring at night.
"Those who take carbonated drinks but that is more of compressed air."
However, some diets produce more gas. Dr Mwasamwaja says, for instance, indigestible carbohydrates, types of fibres, and insolubles.
"Pathogenic infections like amoeba, which alter the normal flora because they have to survive in the lumen."
Dr Mwasamwaja says that even some diseases, like intestinal obstruction, cause gas production because gas diffusion in the body is reduced.
"This is because you do not only pass gas through farting; some of it is absorbed in the blood like carbon dioxide; you breathe out," he says.
Is gas always a sign of poor digestion or an underlying issue?
"Yes, it can be, but not always. Most of the time, it is because you have other symptoms like diarrhoea. For example, if you do not absorb fats appropriately, you have what we call steatorrhea—the presence of excess fat in the stool.
"If you don't absorb carbohydrates and proteins, you not only bloat but also have diarrhoea. You've seen people who are not tolerant to milk; one of their symptoms is not only bloating but diarrhoea."
Severe cases?
In severe dysbiosis (altering the normal flora) cases, Dr Mwasamwaja says faecal transplantation is done. "Meaning they have to take faeces from another person, and they transplant it. Since normal flora is genetic, your family member can donate," he says.
However, in Kenya, that is not being done because there is no faecal bank to be able to characterise and see which works for who.
