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Why does my healthy diet make me so flatulent?

The question

In the last few months, I've started to eat a really healthy diet - lean meats, green veggies. I pass gas quite frequently - and it's very, um, odorous. Is there something I should avoid eating?

The answer

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Believe it or not, most people pass gas about 14 times a day. When undigested foods pass from your small intestine into your large intestine, bacteria that reside in the colon break it down. In the process, this undigested food produces carbon dioxide, oxygen, nitrogen, hydrogen and, in some people, methane. Eventually, these gases leave your body - and that means flatulence.

Some foods have the potential to produce more gas than others. Certain carbohydrates in foods can't be digested in the small intestine and therefore ferment in the colon. Beans (kidney beans, black beans, chickpeas and so on) contain large amounts of a gas-producing carbohydrate called raffinose. So do certain vegetables such as asparagus, broccoli, Brussels sprouts, bok choy, cauliflower and cabbage.

Foods that contain high amounts of the natural sugar fructose also have the potential to produce gas in some people. Onions, artichokes, bell peppers, cucumbers, iceberg lettuce, apples, green grapes, pears, raisins and watermelon are examples of foods high in fructose.

The other culprit that's likely contributing to your gas problem is the increase in soluble fibre you are now consuming by switching to a healthier diet. Soluble fibre is found in oats, oat bran, psyllium-enriched cereals and legumes (beans again) and is broken down in the large intestine where it produces gas.

Try to pinpoint which foods are your triggers. Keep a food diary for two weeks and make a note of excess gas. Look for patterns. Are there a few foods that seem to be responsible?

Portion size might also be the issue. If you eat large portions of foods you suspect cause excess gas, try eating less of them rather than cutting them out of your diet. Doing so might help minimize gas.

You can also try Beano, a digestive enzyme supplement available as tablets or drops in drug stores. If you take it with your first bite of a meal, Beano helps the body digest the gas-producing carbohydrates in legumes and many vegetables.

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As for the odour, well, that's usually caused by trace sulphur compounds, produced by bacteria not found in everyone. It's possible that the mix of bacteria that live in your intestinal tract produce these compounds.

Send dietitian Leslie Beck your questions at She will answer select questions, which could appear in The Globe and Mail and/or on The Globe and Mail web site. Your name will not be published if your question is chosen.

Read more Q&As from Leslie Beck.

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The content provided in The Globe and Mail's Ask a Health Expert centre is for information purposes only and is neither intended to be relied upon nor to be a substitute for professional medical advice, diagnosis or treatment.

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