The symposium “Making sense of fat taste,” organized by Timothy A. Gilbertson (Utah State University), was a wonderful example of multidisciplinary and translational approaches to chemical senses questions. The epidemic of obesity has been closely linked with the increase in dietary fat intake commonly associated with Western diets. In order to gain a more complete understanding of the sensory cues involved in the recognition of dietary fat, a number of laboratories over the past decade have begun to challenge the longstanding notion that pure fat was tasteless and that its only salient cue was its texture. This symposium, focused on research on genes and behavior in both rodents and humans, provided support for the emerging idea that fat, specifically free fatty acid, can activate the gustatory system, a conclusion that is clearly consistent with there being a “taste of fat” in addition to the classic tastes of sweet, sour, salty, bitter, and umami. Shigenobu Matsumura (Kyoto University) discussed the evidence surrounding the identification, characterization, and functional role of identified fatty acid cell surface receptors including the fatty acid transport protein, CD36, and the long chain fatty acid–activated G protein-coupled receptor (GPCR), GPR120.1 Commonalities among the fatty acid transduction pathways in several chemosensory cells required for taste, texture, and post-ingestive responses to dietary fat (i.e., taste cells, trigeminal neurons, and enteroendocrine cells, respectively) were discussed by Tian Yu (Utah State University). She presented molecular and cellular evidence in support of a model for a single transduction pathway for fatty acid involving CD36, fatty acid–activated GPCRs, transient receptor potential (TRP)-like channels, and fatty acid–sensitive delayed rectifying K+ channels. Behavioral data supporting the idea that fatty acids can be recognized by the gustatory system were reviewed by David Pittman (Wofford College) and Richard Mattes (Purdue University). Pittman discussed his own research using a conditioned taste aversion paradigm and short-term taste assays, which conclusively demonstrates that rats can recognize fatty acids. Further, he showed that the gustatory system of obesity-prone rats is more sensitive to fatty acids than the gustatory system of obesity-resistant rats,2 tying together the notion of a role for fat perception in dietary fat intake. Importantly, Mattes provided compelling data consistent with a human capacity to recognize and respond to oral free fatty acid exposure.3 These human studies reinforced the idea that fatty acids are the proximate stimulus (i.e., they directly interact with taste cell surface receptors) for fat taste and that understanding the sensory cues for fat will likely play an important role in understanding the processes that could eventually lead to the control of fat intake, and, ultimately, help stem the epidemic of obesity.
[ Dual labeling of a palatal taste bud showing in situ hybridization (red) for T1R1 and immunocytochemical localization for gustducin (green). Figure supplied by Tom Finger (Adapted from Stone, L.M., J. Barrows, T.E. Finger & S.C. Kinnamon. 2007. Expression of T1Rs and gustducin in palatal taste buds of mice. Chem Senses Mar; 32 (3): 255–256). ]