Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
James H. Hollis
Appetite is the motivation to eat. A better understanding of the factors that influence appetite may aid the development of new or improved strategies for body weight management. Accumulating evidence suggests that there is a correlation between certain ingestive behaviors and obesity. However, whether mastication, a key aspect of ingestive behavior, is associated with body weight is not known.
There is a considerable inter-individual variation in human masticatory performance. Moreover, food characteristics also influence masticatory performance. Despite having a major role in ingestion it is not clear if mastication influences appetite.
In this dissertation, we hypothesize that there is a negative correlation between body weight and the number of chews at the swallowing threshold for a given food. We further hypothesize that increasing the number of chews made before swallowing reduces meal size and promotes postprandial satiety. As there are aging-related changes in both appetite and mastication, we are also interested in the response in both young and older adults so that information gained from our research can be applied in both populations.
A series of experiments have been conducted. In the first study, we collected habitual mastication data from 64 young adults using pizza rolls as the test food. Regression analysis revealed a significant negative association between body mass index (BMI) and the number of chews (P=0.020). Similar results were found for BMI and chewing duration (P=0.005). To further investigate the association between body weight and mastication performance, we recruited 11 young (age 18-40) and 11 older (age ≥65) adults and measured their microstructure of mastication by using an electromyographic recording device. It was found aging and food hardness had a significant impact on mastication and controlling for age and food characteristics, the correlation between BMI and the number of chews was significant (P=0.010). Similarly, a significant negative correlation was found between BMI and other mastication parameters such as maximal bite fore (P=0.002), mean bite force (P<0.001), muscle activity (P<0.001) and chewing rate (P=0.025).
While those results show a negative association between body weight and mastication, it is still not known what physiological mechanism explains these results. We then conducted a study to investigate the influence of masticatory cycles on meal size by asking participants to chew pizza rolls either 100%, 150% or 200% of their baseline number of chews. 47 young adults participated in the study and it was found the ad libitum food intake in the 150% and 200% sessions was reduced by 9.5% (P=0.023) and 14.8% (P=0.001) respectively, compared to the 100% session. A similar intervention was conducted in 18 older adults but there was no difference in the food intake across different test sessions. In both studies, eating rate was significantly reduced when the number of chews was increased.
To investigate the influence of mastication on postprandial satiety in both young and older participants, we conducted studies using a fixed-portion meal, by asking participants to chew each portion of the food either 15 or 40 times before swallowing. For young adults, 40 chews resulted in lower hunger (P=0.009), preoccupation with food (P=0.005) and desire to eat (P=0.002). Meanwhile, plasma concentrations of glucose (P=0.024), insulin (P<0.001) and glucose-dependent insulinotropic peptide (GIP) (P<0.001) were higher following the 40 chews meal. Chewing 40 times before swallowing also resulted in a higher plasma cholecystokinin concentration (P=0.045) and a trend toward a lower ghrelin concentration (P=0.051) but there was no difference in food intake at a subsequent meal (P=0.851). Similar results on subjective appetite in older adults were found. However, the effect of masticatory cycles on plasma concentrations of hormones and glucose were different: although higher levels of insulin, GIP and glucose were observed in 40 chews immediately after eating (P<0.05), they became significantly lower after two or three hours (P<0.05). In addition, no difference on cholecystokinin and ghrelin was found (P>0.05). Moreover, there was a trend toward significance that older adults ate more at the subsequent meal in the 40 chews condition (P=0.066). Those results suggest increasing the number of chews before swallowing suppresses subjective appetite and facilitates glucose absorption in both young and older adults, but the satiating effect was different, probably due to aging-related impairment in appetite response in older adults.
In conclusion, the studies involved in the dissertation suggest body weight is a variable explaining for the inter-individual variation in habitual masticatory performance. The ingestive behavior, characterized by eating slowly and chewing thoroughly, suppresses appetite and influences glycemic response in both young and older adults. Information gained from this dissertation is useful as it provides potential dietary and behavioral strategies for body weight management through increased mastication activity, i.e., choosing hard food that requires more mastication activity and/or eating slowly by increasing the number of chews before swallowing.
Zhu, Yong, "Effect of ingestive behavior on appetite in young and older adults" (2012). Graduate Theses and Dissertations. 12895.