Alteration of oral carbohydrate tolerance during administration of a fiber-free formula diet

Fiber-free formula diets are widely used for medical and experimental purposes. In healthy individuals no major changes of fasting blood glucose have been reported, whereas oral glucose tolerance tests indicate a deterioration of carbohydrate tolerance following ingestion of liquid diets containing certain sugars. We examined carbohydrate tolerance in normal subjects during prolonged administration of a fiber-free semisolid diet containing polysaccharides instead of sugars. In the first experiment, diet A (55% starch, 40% highly polyunsaturated fat, P/S 5.4, 15% protein) served as the sole source of energy for 4 weeks. During this time a progressive deterioration of carbohydrate tolerance was observed, indicated by a gradual increase of the postprandial glycemic response (area under the curve) from -316 to +3874 mg/dl × min without significant alteration of postprandial serum insulin concentrations. For the second study, nutrient relations of the diet were modified (diet B: 45% starch, 40% saturated fat, P/S 0.3, 15% protein). The changes of carbohydrate tolerance during 1 week of feeding diet B were similar to those seen in the first experiment. However, follow-up observations during a subsequent pharmacological trial showed that the changes of postprandial blood glucose curves were reversed within 2 weeks. This was associated with an enhanced serum insulin response. The reason for the different durations of the metabolic effects of diets A and B are not obvious from our data. The time course may have been influenced by the different nutrient intake. Fasting blood glucose concentrations were not sensitive enough to detect the deterioration of carbohydrate tolerance.