When some bacteria digest (or ferment) food substances, they produce acids, water, and gases. The major gases which are produced by bacteria include, primarily, carbon dioxide (CO2), hydrogen (H2), methane (CH4), and small concentrations of aromatic gases. Carbon dioxide is produced by all cells during metabolism, but only bacteria can produce H2 and CH4 as metabolic by-products, and this is accomplished primarily by bacteria which thrive in the absence of oxygen (called anaerobic bacteria). So, if either H2 or CH4 are produced biologically, it tells us that some food substance is exposed to bacterial fermentation.
In the digestive tract, bacteria are normally limited to the colon. Most of the bacteria contained in food are killed by the acidity of the stomach, so the small intestine usually has few bacteria. In some conditions, called “bacteria overgrowth,” bacteria exist in high concentrations in the small intestine. Their presence in that area can interfere with the absorption of some vitamins and other essential foodstuffs, so it is important to diagnose the condition.
The colon is concerned with conserving water and salt by reabsorbing them from the lumenal contents. However, the colon is involved in other functions, some of which depend on having a high bacterial count. Fiber, very popular in breakfast cereals, is not digested in the small intestine, so it undergoes bacterial fermentation in the colon. Short-chain fatty acids (SCFA) produced by that process are absorbed in the colon, and are beneficial to health. It is becoming apparent that substantial amounts of starch (10-20% of foods like legumes) escape digestion in the small intestine and are broken down in the colon, thus, adding to the efficiency of energy production by such foodstuffs. In addition, colonic bacteria contribute to fecal bulk, and the short-chain fatty acids mentioned above reduce colonic pH. These factors may reduce the likelihood of diarrhea, confer some degree of protection against other severe colon problems, and enhance the colonic absorption of metal ions like calcium, magnesium and zinc. Thus, fermentation in the colon is normal, and is important.
Gases which are produced in the colon are reabsorbed and equilibrated with the blood leaving that area. They appear in the lung and cross the capillary membrane into the alveoli, from which they expired during breathing. The alveolar air can be collected with the analytical equipment utilized by AerodiagnosticsTM and analyzed.
Hydrogen and methane are produced in the digestive system primarily only by the bacterial fermentation of carbohydrates (sugars, starches or vegetable fibers), so either of the gases appear in the expired air, it is usually a signal that carbohydrates or carbohydrate fragments have been exposed to bacteria, permitting such fermentation to take place(2). The generation of H2 and/or CH4 will result in the reabsorption of some of these gases into the blood stream from the site of their digestion, and they will appear in the expired air.
Bacteria are ordinarily not present in significant numbers in the small intestine, where digestion and absorption of sugars take place. Therefore, when a challenge dose (eg. lactose) is ingested, the level of hydrogen in the alveolar air will rise significantly within one to two hours (depending on the intestinal transit time) only if the sugar is not digested and, therefore reaches the colon.
The hydrogen breath test is a simple non-invasive procedure which is readily accepted by patients and staff (3),, and which has greater reliability and acceptability than the blood test, according to many reports (1, 4-8). The lower dose of lactose usually does not cause the discomfort and explosive diarrhea frequently seen by malabsorbers who are given the larger dose required for the blood test (9).
A study (10) with over 300 patients showed that gastrointestinal symptoms after a lactose challenge are strongly associated with the amount of H2 excreted; the relationship between blood glucose change and symptom-severity was less evident.
False positive breath-tests are rare, and when they occur they are usually caused by improperly doing the test – allowing the subject to smoke, sleep or eat shortly before or during the test (11). Bacterial overgrowth (from the colon retrograde into the small intestine) can also produce a false-positive breath-test, but it is usually preceded by an elevated fasting breath-H2 level and the response is seen soon after the sugar is ingested (within 20-30 minutes).
The incidence of false-negative results with the breath-test is well below that seen with the blood test (1,4,5). False-negative results are reported to be from 5-15% of all lactose malabsorbers, (12-14) due to a variety of causes. Many of the false-negative reports can be avoided by measuring methane in addition to hydrogen (15) because some methanogenic flora convert colonic H2 to CH4.
1. DiPalma, J.A.; Narvaez, R.M. Prediction of lactose malabsorption in referral patients. Dig Dis Sci. 1988: 33:303
2. Levitt, M.D. Production and excretion of hydrogen gas in man. New Engl. J. Med. 1968; 281:122
3. Metz, G.; Jenkins, D.L.; Peters, T.J.; Newman, A.; Blendis, L.M. Breath hydrogen as a diagnostic method for hypolactasia. Lancet. 1975; 1(7917):1144-7
4. Davidson, G.P.; Robb, T.A., Value of breath hydrogen analysis in management of diarrheal illness in childhood: Comparison within duodenal biopsy. J Ped Gastroenterol Nutr. 1985; 4:381-7
5. Fernandes, J.; Vos, C.E., Douwes, A.C.; Slotema, E.;Degenhart, H.J. Respiratory hydrogen excretion as a parameter for lactose malabsorption in children. Amer J Clin Nutr. 1978; 31:587-602.
6. Newcomer, A.D.; McGill, D.B.; Thomas, R.J.; Hoffmann, A.F. Prospective comparison of indirect methods for detecting lactase deficiency. New Engl J Med. 1975;293:1232-6
7. Douwes, A.C.; Fernandes, J.; Degenhart, H.J. Improved accuracy of lactose intolerance test in children, using expired H2 measurement. Arch Dis Child. 1978; 53:939-42
8. Solomons, N.W.; Garcia-Ibanez, R.; Viteri, F.E. Hydrogen breath test of lactose absorption in adults: The application of physiological doses and whole cow’s milk sources. Amer J. Clin Nutr. 1980; 33:545-54
9. Jones, D.V.; Latham, M.C.; Kosikowski, F.V.; Woodward, G. Symptom response to lactose reduced milk in lactose-intolerant adults. Amer j Clin Nutr. 1976; 29(6):981-4
10. Hermans, M.M.; Brummer, R.J.; Ruijgers, A.M.; Stockbrugger, R.W. The relationship between lactose tolerance test results and symptoms of lactose intolerance. Am J Gastroenterol 1997 (Jun); 92(6):981-4
11. Solomons, N.W. Evaluation of carbohydrate absorption: The hydrogen breath test in clinical practice. Clin Nutr J. 1984; 3:71-78
12. Filali, A.; Ben Hassine, L.; Dhouib, H.; Matri, S.; Ben Ammar, A.; Garoui, H. Study of malabsorption of lactose by the hydrogen breath test in a population of 70 Tunisian adults, Gastroenterol Clin Biol. 1987; 11:554-7
13. Douwes, A.C.; Schaap, C.; van der Kleivan Moorsel, J.M. Hydrogen breath test in school children. Arch Dis Child. 1985; 60:333-7