The role of dietary fiber in satiety, glucose, and insulin: studies with fruit and fruit juice.

Healthy volunteers ingested sugar-equivalent meals of oranges and orange juice and of grapes and grape juice. Satiety, assessed by two subjective scoring systems, was greater after whole fruit than after juice and the return of appetite was delayed. With oranges, as previously reported with apples, there was a significantly smaller insulin response to fruit than to juice and less postabsorptive fall in plasma glucose. With grapes, the insulin response to the whole fruit was, paradoxically, more than that to the juice, while postabsorptive glucose values were similar. The glucose in grapes appeared to be more insulinogenic than that in oranges and apples. Conversely, grape juice evoked less insulin than expected, possibly because its high osmolality delayed gastric emptying. However, diluting it did not increase its insulinogenicity. The plasma insulin and glucose responses to fruit appear to depend on the fiber as well as the glucose content of the fruit.