Bacterial Overgrowth, a common cause of flatulence and diarrhea

Bacterial overgrowth refers to the inappropriate growth of bacteria, commonly found in the large intestine (i.e. colon or large bowel), in the small intestine (small bowel). These bacteria, when found in the small intestine, can cause premature fermentation of nutrients. The result is excessive gas. Thus, the hallmark symptoms are flatulence and when gas production is marked, even abdominal distention.

The symptoms of Bacterial Overgrowth (BO) tend to be chronic, though they may be intermittent. Since starches are the major contributor to fermentation, a no starch diet may improve symptoms, but won't resolve them completely. The condition may occur in any condition that increases the likelihood that large intestine bacteria will be able to survive in the colon. This was first noted in people who had gastric or small intestinal resections. It has subsequently been shown to occur at increased frequency in diabetics, the elderly (>75yo), people taking potent inhibitors of gastric acid production (whose main purpose is not to digest food, but to kill bacteria), and people with known intestinal motility disorders. Impaired motility has been suggested as a contributing mechanism in the elderly and diabetics also.

The alternative medicine concept of "leaky gut syndrome"MAY be an associated or contributing factor to symptoms. However, an abnormal lactulose/mannitol differential absorption, considered the gold standard for defining a leaky gut, is much more common in people with BO compared to those w/o it (Scan J Gastro 32: 556-63, 1997). A component in the therapy for leaky gut, is to re-introduce "beneficial" bacteria into the gut. These generally include several species of lactobacillus (acidophillus being the best known), several species of bifidobacter, and streptococcus thermophillus. This type of therapy has shown efficacy in various intestinal disorders, including antibiotic associated diarrhea (JAMA 275: 870-6, 1996), ulcerative colitis (a non-pathogenic E Coli was as effective as mesalazine, Lancet 354: 635-639, 1999) and infective diarrhea (J Gastro Hepatol 15: 489-493, 2000). In addition, maldigestion due to abnormal fermentation may be a factor in patients suffering from Irritable Bowel Syndrome (Lancet 352: 1187-9, 1998).

The breath testing used to detect bacterial overgrowth generally focuses on hydrogen. People drink 50g of glucose or lactulose. If they maldigest the sugar used, the excrete increased hydrogen in their breath. For unclear reason, a subset of people (5-10%), will convert the hydrogen in their gut to methane. Thus, when the breath test is negative for H2, but symptoms are suggestive, measurement of methane may give the answer. These are the people who tend to have "bad breath" as a major complaint (my anecdotal experience).

Therapy generally includes antibiotics. One could try a Gut Restoration Program, yet I know of no published data to support this. Published studies have shown high efficacy of a metronidazole (Flagyl) and colistin (a non-absorbed antibiotic effective against Enterobacteraceae and Klebsiela) for 10 days (J of Peds 128: 203-7, 1996), rifaximin (a non-absorbable rifabutin like drug similar in efficacy to colistin, Alimentary Pharm and Ther 14: 551-6, 2000), Norfloxacin or Augmentin (Gastro 117: 794-7, 1999 and Diabetes & Metab 24: 530-6, 1998). Tetracycline is a drug that had been traditionally used for BO, but when compared to rifamixin, it was much less effective. The other drugs noted above have shown efficacy rates of 65-80%.

Generally I will begin with flagyl for 10-14 days. I may add coverage of Enterobacteraceae if the person has severe symptoms, or use Augmentin in monotherapy. Often, I will use this broader coverage only if flagyl fails, or if it doesn't produce a durable result. Efficacy is usually easily assessed by monitoring symptoms, but repeat BO breath testing may be done, if documentation of response is warranted. I will often try to get people to eat organic yogurt or Stoneyfield Farm Yogurt, which contain active cultures of the beneficial bacteria on a regular basis to prevent recurrence, but I haven't had good luck with this. I am not sure it has to do with the defect leading to bacterial overgrowth requiring more potent therapy, or if people aren't consuming an adequate dose, or other factors, as noted in the Gut Restoration Program, are required to enhance their efficacy.