Research undertaken by Professor Zverev at the university of Malawi saw 16 non-smoking male undergraduates forgoing breakfast, having eaten a set dinner at 18.30 the previous evening. The researchers then asked the students to sip sugar, salt or quinine solutions of different concentrations, and whether they thought they were tasting sweet, salty or bitter drinks. One hour after lunch, the volunteers repeated the taste tests.
When they were hungry, the students were more sensitive to the presence of sugar and salt in the drinks. Having an empty stomach did not change the volunteers' ability to recognise bitterness, report the scientists.
Professor Zverev suspects that this difference is due to the different roles that the tastes play: "While sweet and salty tastes are indicators of edible substances and trigger consumption, a bitter taste indicates a substance which is not suitable for consumption and should be rejected."
The importance of recognising bitter solutions, in case they are toxic, could also explain why relatively dilute solutions of quinine were recognised as being bitter. Salt or sugar solutions had to be more concentrated before the students could taste them as being salty or sweet.
The students were asked not to swallow the drinks, in case this eased their hunger. Instead they spat them out after tasting, and rinsed their mouth with water in between each test.
The small study is published online this week at BMC Neuroscience.