My answer to What can a gastrointestinal doctor tell about a person just from the smell of their farts?

Answer by Connie b. Dellobuono:

How to prevent smelly farts

The best way to prevent your farts from becoming smelly is to avoid eating foods that are rich in sulfur. Sulfur has an odor of rotten eggs and is notorious for causing foul smelling farts. Foods to avoid include vegetables from the cabbage family such as broccoli, Brussels sprouts, cauliflower, and bok choy. Other foods rich in sulfur are meat, eggs, cheese, whole cow's milk, garlic, onions, horseradish, and sulfite preserved foods like wine and dried fruits.
To minimize malodorous gas, eliminate high sulfite meats like beef and pork from your diet and substitute them with their low sulfur counterparts such as fish and chicken. Use ginger and chili peppers instead of garlic and onions, and eat plenty of the low sulfur containing vegetables including avocados, eggplant, spinach, and carrots.
Maximizing the amount of fresh fruits and vegetables in your diet acts as a natural laxative and helps you to have regular bowel movements. This decreases the amount of time that gas sits in the colon being exposed to odor causing bacteria. When gas is exposed to bacteria for long periods, any food we eat will cause foul smelling farts. To make sure that your bowels move regularly, eat plenty of natural fiber and drink lots of water.
What other conditions are smelly farts symptomatic of?
Foul smelling farts are rarely associated with serious illness. However, if avoiding sulfur containing foods and having regular daily bowel movements does not improve the odor of your farts, or you are experiencing additional symptoms such as weight loss, abdominal pain, nausea, or vomiting, you may have a digestive disorder. These are a few conditions to consider:
Carbohydrate malabsorption: This ranges from mild to severe. The mild form can present as vague abdominal pain with bloating. The severe form is called Celiac disease. It can present with severe abdominal pain and vitamin deficiencies. Both conditions are treated by removing gluten from your diet. Gluten is found in wheat, rye, and barley products such as bread and flour. Avoiding these products improves symptoms associated with this disease.
Lactose intolerance: Lactose is the sugar found in dairy products. When we don't have enough of the enzyme necessary to break lactose down, it remains in our digestive tract for odor causing bacteria to feed on. If you are lactose intolerant, avoiding dairy may be an easy way to decrease the amount of flatulence that you produce and improve its odor.
Infections of the digestive tract: There are many bacteria and viruses that can cause infections in the lining of the digestive tract. Some of these may be associated with travelling to different parts of the world. Infections are usually accompanied by diarrhea, fever, and abdominal pain. If you suspect that you may have an infection, consult your doctor to determine appropriate treatment.
http://www.med-health.net/Smelly-Farts.html

What can a gastrointestinal doctor tell about a person just from the smell of their farts?