The Taste for Fat: New Discoveries on the Role of Fat in Sensory Perception, Metabolism, Sensory Pleasure, and Beyond

Three papers in this issue of Journal of Food Science are the result of a symposium held at the Institute of Food Technologists Annual Meeting; New Orleans, LA; June 12, 2011. Session sponsor: Givaudan Flavors and Fragrances Program participants and resultant papers: Richard D. Mattes, Dept. of Nutrition Science, Purdue Univ. "Are Free-Fatty Acids Effective Taste Stimuli in Humans? (p. S148–151) Edmund T. Rolls, The Oxford Centre for Computational Neuroscience, Oxford, U.K. "Mechanisms for Sensing Fat in Food in the Mouth" (p. S140–142) Kathleen L. Keller, Pennsylvania Dept. of Health and Nutritional Sciences, Pennsylvania State Univ. "Genetic Influences on Oral Fat Perception and Preferences" (p. S143–147) How are fats perceived, and how does the sensation of fat influence the acceptability of fat-containing foods? Ask any sensory scientist or product developer and they will respond that fats are perceived primarily by flavor and texture cues, and that the pleasantness of these 2 components determines a food's palatability and acceptability. This general framework has guided the development of reduced-fat foods for several decades. Nevertheless, despite high consumer interest in healthier eating and a thriving market for low/reduced-fat products, fewer U.S. consumers are seeking nutritional information about fat on food packages (FCIC 2011; Sloan 2012). In the U.K., more than a third of consumers agree that reduced-fat foods have improved in taste, but more than half state they are more interested in taste than calorie or fat content (Mintel 2011). Thus, current products may not be delivering the optimum sensory experience that consumers seek, and new strategies are needed to meet consumer expectations for these foods. Our understanding of the sensory perception of fat has undergone a revolutionary change in the last decade. Animal studies now demonstrate that fats may be perceived in the mouth by gustatory or "taste" mechanisms (Gilbertson and others 2010; Khan and Besnard 2009). Evidence for oral sensing of fats by humans is mounting as well. In this issue of the Journal, Tucker and Mattes (2012) review data showing that humans can detect free-fatty acids, by mouth, when other sensory cues are minimized or blocked. These authors also speculate whether fatty-acids meet the criteria of a true taste primary. That is, do fatty-acids possess unique sensory qualities and do they interact with specialized receptors and/or signaling mechanisms? Recent findings support these speculations. According to Galindo and others (2012), human trained assessors described the oral sensation of fatty acids as 'fatty' and 'scratchy'. Further, putative fatty-acid receptor proteins have also been identified in human taste tissue such as the long-chain fatty-acid transporter CD36, and the G-protein coupled receptor GPR120 (Galindo and others 2012; Simons and others 2009). Since these proteins bind fatty-acids with different chain lengths and degrees of saturation, these findings raise intriguing questions about the nature of the fat-derived signal. Does fatty-acid sensing provide information about the nutritional profile of ingested fat that is not captured by flavor and texture alone? This hypothesis awaits further testing. Neural imagining studies have begun to unmask the subjective experience of fat in the mouth and to connect this experience to liking. The article by Rolls (2012) provides evidence that the texture of fat in the mouth is represented in areas of the cortex that have been implicated in chemosensory perception and sensory pleasure. According to Rolls (2012), fat-sensitive neurons respond to the lubricity (slipperiness) of oil in the mouth but not its viscosity, which is a separate precept. These fat-sensitive neurons also do not respond to free-fatty acids. These data argue that texture may be the primary fat-derived signal in the brain, but they do not rule out the possibility of discovering other neurons that respond to free-fatty acids. Future studies will no doubt examine this possibility. Finally, steady progress has been made in identifying the genes involved in oral fat sensing, and in understanding how variation in these genes might play a role in obesity. In a study in obese African-American adults, Keller (2012) showed that those with a specific sequence variation in the CD36 gene gave higher reported preference ratings for added fats, but they were less able to discriminate differences in creaminess of tasted samples of salad dressings than those without this variation. Keller's findings are complemented by data from another study, also in obese adults, showing that those with this same variation in CD36 had elevated thresholds (that is, low sensitivity) for free oleic acid (Peppino and others 2012). Currently, we do not know if reduced fat sensitivity predisposes some individuals to obesity by promoting higher fat intake or if chronic high-fat diet exposure leads to reduced fat sensitivity and obesity development as proposed by Stewart and others (2011). This critical question deserves additional study. The 2010 Dietary Guidelines for Americans emphasizes the importance of controlling total energy, saturated fats and trans-fats in the diet (http://www.dietaryguidelines.gov/). New tools designed to help consumers plan a healthy diet have recently been introduced (http://www.choosemyplate.gov/) or are in the planning stages (Wartella and others 2011). These initiatives create challenges and opportunities for food scientists to develop the next generation healthier fats and low/reduced-fat foods. Additional research on fat perception will lead to critical advances in knowledge for achieving these goals.