'Fat' May Be the Sixth Taste
Sweet, sour, salty, bitter, and umami are recognized as the five basic tastes. Soon, a sixth may join them: fat.
In truth, it's been a long time coming. Aristotle was one of the first to label fat a fundamental taste back in 350 BC. But, more recently, fat has not been able to pass scientific muster and join the vaunted ranks of sweet and sour.
Russell Keast and Andrew Costanzo, researchers at the Sensory Science Group at Deakin University in Australia, believe fat's standing has changed, however.
"There is consistent emerging evidence that fat is the sixth taste primary," they claim in a new review published to the journal Flavour.
"For fat to be generally accepted as a taste, it must meet five criteria," Keast and Costanzo continue.
First, "There must be a distinct class of affective stimuli..." The breakdown of fats and fatty acids by lipases serves as the stimuli.
Second, "There should be transduction mechanisms including receptors to change the chemical code of the stimuli to electrical signal..." Recently, a receptor called CD36 has been identified on taste bud cells that appears to detect the arrival of fatty acids.
Third, "There must be neurotransmission of the electrical signal to processing regions of the brain." Transduction events triggering the release of neurotransmitters to the brain have been observed.
Fourth, "there must be physiological effects after activation of taste bud cells." Fat's presence in the human mouth triggers as much as a 2.8-fold increase in plasma triglyceride levels.
Fifth, "There should be perceptual independence from other taste qualities..." Here, there's a bit of a sticking point. While the perception of fat is undoubtedly different than "sweet" or "salty," there's debate as to whether or not it offers a unique taste quality.
Fat's status as an official taste is borderline semantic. Prior research conducted by Keast has demonstrated that people who are more "sensitive" to certain fatty acids consume fewer fatty foods in their diets, while those less sensitive consume more.
In conclusion, biology textbooks don't require revision just yet. But Keast and Costanzo predict that fat's status as a taste will be settled relatively soon, within the next five to ten years.
Source: Keast and Costanzo: Is fat the sixth taste primary? Evidence and implications. Flavour 2015 4:5.