I went on a low carb diet recently, and I have been gassy ever since. Why?

Some of the sugar substitutes on a low carbohydrate or sugar free diet are actually man-made artificial sweeteners which are indigestible sugars. These include sorbitol, mannitol, maltitol, xylitol, and Splenda. The first four of these sugars are found in sugar free chewing gum, dietetic candies, and dietetic cookies. Splenda is a man-made sugar which is found in many diet beverages and which is available in large boxes with a recommendation to be used as a sugar substitute for baking. The small intestine does not contain the necessary enzymes to digest (break down) these artificial sugars, and as a result, the undigested (intact) artificial sugar molecules travel through the small bowel to reach the colon, where the colonic bacteria ferment them, producing carbon dioxide, methane, or hydrogen gas. These gases can be produced in sufficient quantities to produce cramps and flatulence. Sometimes, the passage of these sugars to the colon draws fluid into the channel of the bowel so that the person experiences diarrhea. Symptoms can be particularly intense for the person who takes these sugar substitutes regularly and probiotics regularly, since the probiotic bacteria will ferment these sugars in the small and large bowel.