Effect of Fructose on Colonic Microflora

The concept of Colonic Adaptation(CA) to regular carbohydrates has been linked mainly to lactose disaccharide(galactose,glucose) and lactulose(galactose, fructose), a manufactured derivative of lactose. CA is achieved in both cases by short term regular consumption of the targeted sugar which is not digested by the host. The clinical definition of CA includes a measured change in breath hydrogen, reduction of clinical symptoms (Bloat, gas, cramps and at times diarrhea) and an associated increase of bacterial lactase(β-galactosidase. The putative mechanism is through bacterial action which results in enhanced metabolism or expanded bacterial population of specific genus and species of bacteria. The act of CA may incur health benefits through physicochemical changes and especially promotion of health promoting bacteria.

Maldigestion of fructose occurs in the population probably in a dose dependent fashion. The sugar content overwhelms the principal GLUT5 intestinal carrier. In the presence of glucose this non energy dependent system works better(11). In a previous publication we found that the pre test graded ingestion of fructose had no impact on test results. These results were dramatically different from that found for pretest lactose ingestion. The investigators interpreted the results from the fructose study as being consistent with a failure to show CA to regular fructose consumption.

More recently Rao et al however, showed that there may be a threshold level of intake beyond which fructose maldigestion may rapidly increase. This value was thought to be 15-20g. In the case of lactose this was 10g(15). Since in both our studies we used the same dose response analysis(<10,11-19, and >20g/d), it is possible that fructose consuming individuals might not have spilt adequate quantities of fructose into the colon to properly induce and maintain CA. Moreover, there is to our knowledge no information on a possible prebiotic effect of the monosaccharide fructose. Since polymers of fructose are very good prebiotics it may be of interest to determine whether this sugar is capable of prebiotic function in its own right.

The investigators propose to carry out a short term study on 20-30 healthy participants to determine whether a 2 week period of fructose consumption alters clinical CA and intestinal microflora.

Study Outline After an overnight fast, except for water(ad libitum), participants present themselves to the GI lab around 9 am. A 50 gm fructose solution (this dose is associated with a 65% chance of maldigestion(14))will be administered. Breath hydrogen and symptoms will be recorded for 4.5 Hrs at ½ hr intervals. Participants will be asked to fill out a short 3 day diet recall questionnaire targeting fructose ingestion.

Participants will be asked to consume 30g fructose in 150ml of water (lemon juice may be added) twice a day for 14 days.They will then return for a repeat50 g fructose challenge. A small stool sample will be asked from participants at each test period.Another similar group will undergo the same tests but without taking intervening fructose.