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There are numerous and diverse factors enabling the overconsumption of foods, with the sense of taste being one of these factors. There are four well established basic tastes: sweet, sour, salty, and bitter; all with perceptual independence, salience, and hedonic responses to encourage or discourage consumption. More recently, additional tastes have been added to the basic taste list including umami and fat, but they lack the perceptual independence and salience of the basics. There is also emerging evidence of taste responses to kokumi and carbohydrate. One interesting aspect is the link with the new and emerging tastes to macronutrients, with each macronutrient having two distinct perceptual qualities that, perhaps in combination, provide a holistic perception for each macronutrient: fat has fat taste and mouthfeel; protein has umami and kokumi; carbohydrate has sweet and carbohydrate tastes. These new tastes can be sensed in the oral cavity, but they have more influence post- than pre-ingestion. Umami, fat, kokumi, and carbohydrate tastes have been suggested as an independent category named alimentary. This narrative review will present and discuss evidence for macronutrient sensing throughout the alimentary canal and evidence of how each of the alimentary tastes may influence the consumption of foods.

Fatty acid taste (FAT) perception is involved in the regulation of dietary fat intake, where impaired FAT is associated with increased fatty food intake. There are a number of FAT receptors identified on human taste cells that are potentially responsible for FAT perception. Manipulating dietary fat intake, and in turn FAT perception, would elucidate which receptors are associated with long-term regulation of FAT perception. This study aimed to assess associations between diet-mediated changes to FAT receptors and FAT perception in humans. A co-twin randomized controlled trial was conducted, where each matching twin within a pair were randomly allocated to either an 8-week low-fat (LF; <20% energy fat) or high-fat (HF; >35% energy fat) diet. At baseline and week 8, fungiform papillae were biopsied in the fasted state and FAT receptor gene expressions (CD36, FFAR2, FFAR4, GPR84 and KNCA2) were measured using RT-PCR; and fatty acid taste threshold (FATT) was assessed using 3-alternate forced choice methodology. Linear mixed models were fitted, adjusting for correlation between co-twins. Intakes were compliant with the study design, with the LF and HF groups consuming 14.8% and 39.9% energy from fat, respectively. Expression of FFAR4 increased by 38% in the LF group (P=0.023; time-diet interaction P=0.063). ΔFFAR4 (Δ, week 8 - baseline) was associated with Δfat intake (g) (β=-159.4; P<0.001) and ΔFATT (β=-8.8; P=0.016). In summary, FFAR4 is involved in long-term diet-mediated changes to FAT perception. Manipulating dietary fat intake, and therefore FFAR4 expression, might aid in reducing taste-mediated passive overconsumption of fatty foods.

Fat provides important sensory properties to baked food products, such as colour, taste, texture and odour, all of which contribute to overall consumer acceptance. Baked food products, such as crackers, cakes and biscuits, typically contain high amounts of fat. However, there is increasing demand for healthy snack foods with reduced fat content. In order to maintain consumer acceptance whilst simultaneously reducing the total fat content, fat replacers have been employed. There are a number of fat replacers that have been investigated in baked food products, ranging from complex carbohydrates, gums and gels, whole food matrices, and combinations thereof. Fat replacers each have different properties that affect the quality of a food product. In this review, we summarise the literature on the effect of fat replacers on the quality of baked food products. The ideal fat replacers for different types of low-fat baked products were a combination of polydextrose and guar gum in biscuits at 70% fat replacement (FR), oleogels in cake at 100% FR, and inulin in crackers at 75% FR. The use of oatrim (100% FR), bean puree (75% FR) or green pea puree (75% FR) as fat replacers in biscuits were equally successful.

Evidence suggests individuals less sensitive to fat taste (high fat taste thresholds (FTT)) may be overweight or obese and consume greater amounts of dietary fat than more sensitive individuals. The aims of this study were to assess associations between FTT, anthropometric measurements, fat intake, and liking of fatty foods. FTT was assessed in 69 Australian females (mean age 41.3 (15.6) (SD) years and mean body mass index 26.3 (5.7) kg/m²) by a 3-alternate forced choice methodology and transformed to an ordinal scale (FT rank). Food liking was assessed by hedonic ratings of high-fat and reduced-fat foods, and a 24-h food recall and food frequency questionnaire was completed. Linear mixed regression models were fitted. FT rank was associated with dietary % energy from fat ( β ^ = 0.110 [95% CI: 0.003, 0.216]), % energy from carbohydrate ( β ^ = -0.112 [-0.188, -0.035]), and frequency of consumption of foods per day from food groups: high-fat dairy ( β ^ = 1.091 [0.106, 2.242]), meat & meat alternatives ( β ^ = 0.669 [0.168, 1.170]), and grain & cereals ( β ^ = 0.771 [0.212, 1.329]) (adjusted for energy and age). There were no associations between FT rank and anthropometric measurements or hedonic ratings. Therefore, fat taste sensitivity appears to be associated with short-term fat intake, but not body size in this group of females.

Taste is the chemical sense responsible for the detection of non-volatile chemicals in potential foods. For fat to be considered as one of the taste primaries in humans, certain criteria must be met including: class of affective stimuli; receptors specific for the class of stimuli on taste bud cells (TBC); afferent fibers from TBC to taste processing regions of the brain; perception independent of other taste qualities; and downstream physiological effects. The breakdown products of the macronutrients carbohydrates (sugars) and protein (amino acids) are responsible for activation of sweet and umami tastes respectively. Following the same logic the breakdown products of fat being fatty acids are the likely class of stimuli for fat taste. Indeed, psychophysical studies have confirmed fatty acids of varying chain length and saturation are orally detectable by humans. The most likely fatty acid receptor candidates located on TBC are CD36, G protein-coupled receptor 120. Once the receptors are activated by fatty acids a series of transduction events occurs causing the release of neurotransmitters towards afferent fibers signalling the brain. Whether fatty acids elicit any direct perception independent of other taste qualities is still open to debate with only poorly defined perceptions for fatty acids reported. Others suggest that the fatty acid taste component is at detection threshold only and any perceptions are associated with either aroma or chemesthesis. It has also been established that oral exposure to fat via sham feeding stimulates increases blood triacylglycerol concentrations in humans. Therefore, overall, with the exception of an independent perception, there is consistent emerging evidence that fat is the sixth taste primary. The implications of fatty acid taste go further into health and obesity research with the gustatory detection of fats and their contributions to energy and fat intake receiving increasing attention. There appears to be a coordinated bo