A double-blind randomized cross-over study was performed. Six subjects participated in two experimental sessions after a 10-12 hr overnight fast with a 2-week interval in between. They received either 1000 mg of encapsulated OFI-extract (OpunDiaTM, an aqueous extract of OFI; Finzelberg GmbH & Co. KG, Germany), or placebo capsules (LUVOS Heilerde) with identical appearance.
Thirty min after ingestion a 2-hr oral glucose tolerance test (OGTT: 75g of glucose in 300ml water; blood samples (5ml) at 0, 30, 60, 90, and 120 min) was started. Plasma samples were assayed for glucose and insulin concentration. Immediately after this OGTT the subjects performed a cycling exercise bout on an electromagnetically braked bicycle ergometer (Avantronic Cyclus 2, Leipzig, Germany). Following a 10-min warming up (5min @ 60 Watt + 5min @ 120 Watt), they cycled for 30min at a ~70% workload of VO2max. After this exercise bout they received another dose of either 1000 mg of encapsulated OFI-extract, or placebo capsules. Then a second 2-hr OGTT started. However, in this OGTT a dual glucose bolus was administered (75g glucose in 300 ml at time 0 and at time 60 min). Student's paired T-tests were used to evaluate treatment effects. A probability level (p< 0.05) was considered statistically significant.