A Review of the Evidence Supporting the Taste of Non‐esterified Fatty Acids in Humans

Abstract

Historically, each was primarily ingested as a macromolecule with limited taste activity (i.e., our evolutionary ancestors were unlikely to have the plethora of sweet carbohydrate foods that we have; even fruits would have been much less sweet before the advent of agriculture). The signal was amplified in the oral cavity through the oral phase of digestion, but to a large degree, decisions to swallow energyyielding foods were based on subtle, transient taste sensations. This observation is relevant to any discussion of taste primaries as it indicates strength or clarity of sensation is not a critical defining property.A compelling case can be made that sweet taste exists to facilitate the discovery of carbohydrate in the environment and its ingestion [1]. Carbohydrate generally, and simple sugars more specifically, are often vilified as contributors to chronic disease risk. However, it should be noted that detection and desired consumption of carbohydrate, including simple sugars, is highly adaptive. The sugar lactose constitutes about 40 % of the energy of breast milk and glucose is used by every cell in our bodies. Though some natural products contain high concentrations of simple sugars (e.g., honey, some fruits), starch was, and is, the predominant form of dietary carbohydrate. Accumulating evidence suggests starch is an effective taste stimulus in rodents [2, 3] and possibly in humans [4], but it must be hydrolyzed by salivary amylase to mono-or disaccharide units in the oral cavity to elicit a clear signal of sweetness. Among those subscribing to the concept that the sense of taste is comprised of a limited number of primary qualities, sweetness is universally recognized as a taste primary, but the starchiness of carbohydrates is not.In nature, proteins are also weak taste stimuli. The recent identification of the T1R1-T1R3 glutamate receptor is reported to code for a unique quality that aids identification of protein sources in the environment [5,6]. The Abstract Dietary fats contribute to the flavor of foods by multiple mechanisms. A role for their taste has only recently gained credence. Current evidence indicates non-esterified fatty acids (NEFA) are the effective stimuli for the taste component. CD36 and GPR120 are putative receptors, but may not fully account for the totality of the range of sensations elicited by fatty acids. The sensory quality of long-chain NEFA is not adequately characterized by commonly accepted taste primary qualities and has been termed oleogustus. There is marked individual variability in sensitivity to the taste of NEFA prompting hypotheses of genetic and environmental determinants. Though an association with BMI has been proposed, the preponderance of evidence is not supportive. The importance of oleogustus has not been fully established, but likely contributes to flavor, which influences food choice as well as lipid metabolism and chronic disease risk. A better understanding of oleogustus may provide insights useful for product formulation.

Protein Leverage: Theoretical Foundations and Ten Points of Clarification

“…A mechanism for achieving nutritionally balanced intake is to have separate regulatory systems for different nutrients (specific appetites), which ensure that each is obtained at, or close to, the required level through a combination of food selection (complementary feeding; Figure A) and control of intake. Nutrient‐specific taste responses, known to include all three macronutrients (carbohydrates, both sugar [sweet] and starch) , amino acids (umami), fats , and salt , are one component of such systems. In both vertebrates and invertebrates, these taste responses are integrated with other system components that motivate the animal to eat the particular nutrient and regulate its intake to the required level.…”

Taste Responses to Linoleic Acid: A Crowdsourced Population Study

“…Additionally, we cannot exclude the possibility that the quality changes with concentration, and the heritability is stronger for the quality associated with the high concentration. It is clear that the quality changes with fatty acid chain length where it is sour for short-chain fatty acids and shifts to oleogustus for long-chain fatty acids ( Running et al 2015 ; Running and Mattes 2016 ). Finally, our heritability estimate is modest (19%).…”

Studies of human twins reveal genetic variation that affects dietary fat perception

“…The sweetness of sugar is well understood from a sensory perspective (Nelson et al 2001), with direct links between taste cells and brain areas of reward (e.g., (Veldhuizen et al 2017)). In contrast, the initial sensory steps responsible for the perception of dietary fat are less well understood, and what is known is contentious: whether there is a distinct taste quality for fat or fatty acids, and which of the chemical and texture components of fat are responsible for the sensations it evokes (Reed and Xia 2015; Running et al 2015; Running and Mattes 2016).…”

“…One unresolved conundrum is mounting evidence that, while triglycerides and fatty acids both impart fatty sensations in foods, triglycerides tend to have a positive hedonic valance, e.g.,(Bakke et al 2016) whereas fatty acids typically have a negative hedonic valence, e.g., scratchy (Voigt et al 2014) or otherwise “bad” (Running and Mattes 2016). These data suggest multiple sensory pathways are involved in the perception of fats in foods (Drewnowski 1992).…”