The main problem with cronic constipation is that with the wrong diet, or some use of antibiotics, and stress, there's a possibility that the microflora of the gastrointestinal tract can become disbalanced. This dysbiosis may cause bad breath. Probiotics along with an intestinal cleansing and proper diet can restore the microflora of the gut to its proper balance. See a post I did here in CureZone regarding probiotics, http://curezone.com/forums/fm.asp?i=1211835.
There's an article in the Alternative Medicine Review, June, 2004 by Hawrelak JA, Myers SP, that addresses the issues of dysbiosis. This 19-page article of the Alternative Medicine Review, presents an in-depth discussion of the causes of intestinal dysbiosis, a state of imbalance of the intestinal flora. It describes the microflora of the gastrointestinal tract as having “an ecosystem of the highest complexity…composed of over 50 genera of bacteria accounting for over 500 different species.” Of particular interest are the factors that can alter the gastrointestinal microflora, such as the use of antibiotics, physical and psychological stress, and dietary changes. On a positive note, the authors concludes that altering our diet, attenuating stress, and using antibiotics sparingly, can minimize or at least attenuate, and thus manipulate the microflora to become more successful and longer-lasting in effect. The authors' base was The Australian Centre for Complementary Medicine Education & Research