Olfactory influences on appetite and satiety in humans

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Fluid or fuel? The context of consuming a beverage is important for satiety

Energy-containing beverages have a weak effect on satiety, limited by their fluid characteristics and perhaps because they are not considered ‘food’. This study investigated whether the context of consuming a beverage can influence the satiating power of its nutrients. Eighty participants consumed a lower- (LE, 75 kcal) and higher-energy (HE, 272 kcal) version of a beverage (covertly manipulated within-groups) on two test days, in one of four beverage contexts (between-groups): thin versions of the test-drinks were consumed as a thirst-quenching drink (n = 20), a filling snack (n = 20), or without additional information (n = 20). A fourth group consumed subtly thicker versions of the beverages without additional information (n = 20). Lunch intake 60 minutes later depended on the beverage context and energy content (p = 0.030): participants who consumed the thin beverages without additional information ate a similar amount of lunch after the LE and HE versions (LE = 475 kcal, HE = 464 kcal; p = 0.690) as did those participants who believed the beverages were designed to quench-thirst (LE = 442 kcal, HE = 402 kcal; p = 0.213), despite consuming an additional 197 kcal in the HE beverage. Consuming the beverage as a filling snack led participants to consume less at lunch after the HE beverage compared to the LE version (LE = 506 kcal, HE = 437 kcal; p = 0.025). This effect was also seen when the beverages were subtly thicker, with participants in this group displaying the largest response to the beverage’s energy content, consuming less at lunch after the HE version (LE = 552 kcal, HE = 415 kcal; p<0.001). These data indicate that beliefs about the consequences of consuming a beverage can affect the impact of its nutrients on appetite regulation and provide further evidence that a beverage’s sensory characteristics can limit its satiating power

Optimising foods for satiety

Foods that generate strong satiety sensations have obvious ben- efits for weight management. This review builds on the under- standing that a food’s satiating power is dependent on the amount of protein, carbohydrate, fat and fibre it contains by examining evidence that the consumer’s sensory and cognitive appraisal of the food is also important. It is concluded that numerous features of a food product can be manipulated to enhance the consumer’s experience of satiety but the combi- nation of these features will ultimately determine its effect on appetite control. Taking this integrated approach to satiety will optimise the development of high satiety foods

That smells filling: effects of pairings of odours with sweetness and thickness on odour perception and expected satiety

Retronasal co-experience of odours with sweet tastes and thick textures have been shown to result in attribution of sweetness and thickness to odours when they are subsequently sniffed. Orosensory thickness and creaminess are also associated with expectations that a product will be filling. Here we test for the first time whether co-experience of odours with orosensory thickness and sweetness results in transfer of satiety expectations to these odours when subsequently sniffed. Eighty healthy volunteers evaluated the hedonic and sensory characteristics of odours, and expectations that products with the same flavour as the odour would be filling, before and after disguised co-experience of odours with sweetness (sucrose), thickness (tara gum solution) or the combination of sweet/thick, as well as untrained (control) odours. Odours paired with tara gum were subsequently rated as smelling thicker and more creamy, while odours paired with sucrose smelled sweeter. Pairing odours with tara gum increased the expectation that products predicted to have the same flavour as the sniffed odour would be more filling, and this was enhanced by sweetness, while pairing odours with tara-gum increased the expectation that products with that odour would reduce later hunger. Liking for odours paired with sweetness increased, but pairing with thickness alone reduced liking. These data suggest that satiety-consonant sensory characteristics can transfer to associated odours, and that this process is independent of changes in liking. This raises the possibility of using satiety-associated odour cues to manipulate consumer satiety expectations

Smelling the goodness: sniffing as a behavioral measure of learned odor hedonics

Pairing an odor and taste can change ratings of the odor’s perceptual and hedonic characteristics. Behavioral indices of such changes are lacking and here we measured sniffing to assess learned changes in odor liking due to pairing with sweet and bitter tastes. Participants were divided on their liking for sweetness, as well as dietary disinhibition (TFEQ-D scale), both of which influence hedonic odor-taste learning. In sweet likers, both sniff duration and peak amplitude increased for the sweet-paired odor. Sniff magnitude decreased for sweet- and quinine-paired odors in sweet-dislikers, and sweet likers smelling the quinine-paired odor. In sweet-likers, liking for the sweet-paired odor increased with both TFEQ-D score and hunger, and sniff magnitude with TFEQ-D only. There were no predictors of changes in response to the quinine-paired odor. Brief co-experience of odors with sweet tastes can lead therefore to measurable changes in sniffing, providing a novel behavioral index of odor liking

Effects of repeated consumption on sensory-enhanced satiety

Previous research suggests that sensory characteristics of a drink modify the acute satiating effects of its nutrients, with enhanced satiety evident when a high energy drink was thicker and tasted creamier. The present study tested whether this modulation of satiety by sensory context was altered by repeated consumption. Participants (n=48) consumed one of four drinks mid-morning on seven non-consecutive days with satiety responses measured pre-exposure (day 1), post-exposure (day 6) and at a one month follow-up. Drinks combined two levels of energy (lower energy, LE, 326 KJ: higher energy, HE, 1163KJ) with two levels of satiety-predictive sensory characteristics (low-sensory, LS, or enhanced sensory, ES). Test lunch intake 90 minutes after drink consumption depended on both the energy content and sensory characteristics of the drink before exposure, but on energy content alone at post-exposure and the follow-up. The largest change was an increase in test meal intake over time in the LE/LS condition. Effects on intake were reflected in appetite ratings, with rated hunger and expected filling affected by sensory characteristics and energy content pre-exposure, but were largely determined by energy content post exposure and at follow up. In contrast, a measure of expected satiety reflected sensory characteristics regardless of energy content on all three test days. Overall these data suggest that some aspects of the sensory-modulation of satiety are changed by repeated consumption, with covert energy becoming more effective in suppressing appetite over time, but also suggest that these behavioural changes are not readily translated into expectations of satiety

Expectations about satiety and thirst are modified by acute motivational state

Prior research has shown that consumers have clear and measurable expectations about the likely effects of food and drink items on their appetite and thirst, which are acquired with experience and influenced by a product’s taste and texture. What is unclear is whether expression of these expectations also varies with current appetitive state. It is possible that current appetite could increase or decrease the relevance of these expectations for future food choice and magnify a product’s expected impact on appetite. To test this, we contrasted expectations about satiety and thirst for four products consumed two hours after an appetite manipulation at breakfast, achieved through ad libitum access to low-energy drinks only (hunger condition), cereal only but no drinks (thirst condition) or both foods and drinks (sated condition). The test products were two soups and two drinks, with a thicker and thinner version of each product type to act as positive control to ensure sensitivity in detecting differences in expectations. For satiety, the predicted differences between products were seen: soups and thicker products were expected to be more filling and to suppress subsequent hunger more than drinks and thinner products, but these differences were more pronounced in the hunger than thirsty or sated conditions. Being thirsty also enhanced expectations of how much drinks would appease immediate thirst. Overall the data show that expectations were adjusted subtly by a person’s current appetitive state, suggesting that we have mechanisms that highlight the most important features of a product at the time when it may be most beneficial to the consumer

Testing a load theory framework for food-related cognition

The way we process rewarding stimuli is widely held to play a key role in normal and abnormal behavior. Biased processing of food—arguably the most primal form of reward—has been strongly implicated in the obesity crisis. Paradoxically, however, existing evidence suggests that both too much and too little attention can potentially lead to overeating. Here we sought to explain this contradiction within the framework of the load theory of attention, while also elucidating the relatively understudied role of memory biases. In 3 experiments, we presented food and nonfood images as irrelevant distractors during a letter search task with high and low levels of perceptual load, followed by a forced choice recognition task. As predicted, increasing perceptual load consistently powerfully reduced distraction by food and nonfood images alike. Similarly, food images encountered under high perceptual load were less likely to be recognized in a surprise memory test. Unexpectedly, however, there was a striking absence of attentional bias to food above and beyond salient nonfood stimuli, either within-subjects or in relation to traits implicated in food-biases. By contrast, a food memory bias was consistently observed across participants, and appeared independent of attentional biases. Food memory was consistently heightened in individuals with high levels of trait disinhibition (a measure of opportunistic eating). Our findings suggest that attention and memory for food and nonfood are similarly impacted by perceptual load. We discuss implications of the load theory framework for the wider literature on food-related cognition and for real world eating behaviors

Perceived thickness and creaminess modulates the short-term satiating effects of high protein drinks

Previous research suggests that increasing beverage protein content enhances subsequent satiety, but whether this effect is entirely attributable to post-ingestive effects of protein or is partly caused by the distinct sensory characteristics imparted by the presence of protein remains unclear. To try and discriminate nutritive from sensory effects of added protein, we contrasted effects of three higher energy (c. 1.2MJ) and one lower energy (LE: 0.35MJ) drink preloads on subsequent appetite and lunch intake. Two higher energy drinks had 44% of energy from protein, one with the sensory characteristics of a juice drink (HP-) and the second thicker and more creamy (HP+). The high-carbohydrate preload (HC+) was matched for thickness and creaminess to the HP+ drink. Participants (healthy male volunteers, n=26) consumed significantly less at lunch after the HP+ (566g) and HC+ (572g) than after HP- (623g) and LE (668g) drinks, although the compensation for drink energy accounted for only 50% of extra energy at best. Appetite ratings indicated that participants felt significantly less hungry and more full immediately before lunch in HP+ and HC+ compared to LE, with HP- intermediate. The finding that protein generated stronger satiety in the context of a thicker creamier drink (HP+ but not HP-), and that an isoenergetic carbohydrate drink (HC+) matched in thickness and creaminess to the HP+ drink generated the same pattern of satiety as HP+ both suggest an important role for these sensory cues in the development of protein-based satiety

Additive effects of sensory-enhanced satiety and memory for recent eating on appetite

The sensory characteristics of a product have been shown to interact with actual nutrient content to generate satiety. Separately, cued recall of recent eating has also been shown to reduce food intake. Here we explore for the first time how these two effects interact, with the hypothesis that sensory enhancement of satiety might be mediated by more vivid memory of the earlier consumed item. On each of two test sessions, 119 women volunteers consumed a control drink (lemonade) on one morning and then one of two test drinks on the next day 30 min before an ad libitum lunch. The test drinks were equicaloric but one was noticeably thicker and creamier, and expected to generate stronger satiety. Just prior to the test lunch, participants were asked to recall either the test drink (test recall) or the drink from the previous day (control recall). Overall, lunch intake was significantly lower after the thicker and creamier (enhanced sensory ES) than thinner (low sensory: LS) test drink (p < 0.001, η2 = 0.11) regardless of recall condition (p = 0.65, η2 < 0.01), but was significantly lower after the test than control recall condition (p < 0.001, η2 = 0.14). Rated hunger was lower after consuming the ES than LS drink both immediately after consumption (p < 0.001, η2 = 0.11) and prior to the test lunch (p = 0.007, η2 = 0.06), while rated hunger just before lunch tended to be lower after recalling the test than control drink (p = 0.052, η2 = 0.03) regardless of the sensory characteristics (p = 0.27, η2 = 0.01). Overall these data further demonstrate the power of ‘sensory-enhanced satiety’ and cued recall of earlier eating as methods to reduce acute food intake, but suggest these effects operate independently