The role of oral exposure to taste on meal termination

Background and aim
The rise in obesity over the last decades is considered to be related to changes in the food environment. Our current diet exists of foods that facilitate fast intake of energy and minimal oral processing. Various studies showed that higher eating rate leads to higher food intake, and therefore promote energy overconsumption. When consuming at a high eating rate, the food spends less time in the oral cavity, resulting in less sensory exposure per gram food. The exposure to the taste of the food in the oral cavity is potentially important in controlling food intake. The studies in this thesis investigated the principle mechanisms through which orosensory exposure affects satiation. The factors that were studied were taste intensity, oral residence duration and bite size. The impact of these factors and their relative contributions to satiation will provide tools for designing new foods to prevent overconsumption.
Methods
We conducted five studies. The subjects that participated in the studies were healthy young normal weight adults. Satiation was measured by ad libitum intake and subjective ratings of hunger and fullness. Tomato soup was used as test product in all studies. We started by investigating the effect of taste intensity on ad libitum intake (n=48). Salt was used to vary the taste intensity in soup. We selected two salt concentrations for low-salt and high-salt soup that were similar in pleasantness on an individual basis. In the next study, salt taste intensity in soup was investigated again, but this time we changed the state of hunger (a preload was offered) and the meal composition (subjects were served a second course after the soup) (n=43). In the third study, the impact of taste intensity versus the duration of orosensory exposure (manipulated by changing the bite size) on satiation was investigated, by using peristaltic pumps to control the bites (n=55). The fourth study focussed on the underlying mechanisms of bite size on food intake (n=56). Therefore, separate effects of oral residence duration per gram food and number of bites per gram food on ad libitum intake were assessed. Finally, we investigated if bite size affects the perceived food intake. Subjects estimated the amount consumed after intake with small or large bites, in both focussed and a distracted states (n=53). In addition, effects of distraction on bite size were investigated.
Results
Taste intensity did not affect ad libitum intake when the soup was presented as single lunch-item in a hungry state. However, higher taste intensity reduced ad libitum intake by ~8%, when the soup was presented after a preload or as a starter followed by a second meal. Smaller bite sizes decreased ad libitum intake by ~25% and did not interact with taste intensity. That smaller bites are more satiating than larger bites was confirmed by hunger and fullness ratings. Hunger decreased faster per consumed gram food when consuming with small bites compared to large bites. A similar effect was found for the increase in fullness. Ad libitum intake was separately reduced by longer oral residence duration and higher number of bites per gram food, there was no interaction between the two variables. Time-intensity measurements showed that both higher number of bites and longer oral residence duration increase the total magnitude of orosensory exposure to the taste of the food. Consumption with large bites resulted in underestimations of the amount consumed, whereas consumption with small bites did not. Distraction increased ad libitum intake. Distraction led to a higher number of bites over the meal but did not affect bite size.
Conclusions
This thesis demonstrates that consuming foods with smaller bite sizes, longer oral residence durations and higher taste intensities lowers food intake. These effects are possibly explained through their enhancement of the orosensory exposure to the taste of the foods. Consumption with large bites leads to underestimation of the amount that is consumed. An underestimation of the amount consumed is a risk factor for overconsumption. These results could be used by the food industry to enhance the satiating capacity of foods in order to prevent overconsumption and decrease the prevalence of obesity.