Fixed. Whatever makes the difference for the individual, it won't be the difference between "natural" and "added" sugar. Maybe the hard biscuit takes longer to digest, or fat in the biscuit slows down digestion.

Coffee or tea with the test meal--if it's biscuits, maybe not, just dipping the biscuit in your tea could make a difference. Or there could be an effect of caffeine on fat metabolism or digestion that changes the difference in sugar absorption between the two foods. Controlled conditions can favour one tested food vs. another.