Abstract: This study aimed to determine whether there might be differences in masticatory performance and eating behaviors by gender and obesity status. Forty eight (24 males; 24 females) non-obese and pre-obese young adults were matched for age, gender, and dental health. Eating behaviors were assessed using the Three-Factor Eating Questionnaire (TFEQ), and chewing performance while eating 152 g of boiled rice was measured using electromyography (EMG). Compared with non-obese participants, pre-obese participants had significantly higher levels of disinhibition according to the TFEQ (P < 0.05 for males; P < 0.01 for females). Microstructures of chewing performance were significantly different by gender but not by obesity status. Males had a greater bite size (P < 0.05), greater chewing power (P < 0.001) and a faster eating rate (P < 0.05) than females. Females habitually chewed more (P < 0.05) and had a longer meal duration (P < 0.01) than males. Eating rate was positively associated with disinhibition (r = 0.490, P < 0.05) score in males. Bite size (r = − 0.449, P < 0.05 for non-obese) and chewing power (r = − 0.581, P < 0.01 for non-obese and r = − 0.446, P < 0.05 for pre-obese) were negatively associated with disinhibition score. Results suggest that the effects of gender and, in part, obesity on eating responses may be explained as chewing performance. Therefore, gender-specific interventions and counseling aimed at slowing the rate of ingestion could be promising behavioral treatments for obese persons.
Alex’s Notes: A previous meta-analysis found that eating rate was associated with greater caloric intake, which may due to several biofeedback mechanisms such as chewing speed, sensory exposure, and satiety hormones. However, how people chew can vary widely between persons, and the current study utilized EMG activity to determine the chewing differences between normal-weight and overweight men and women.
Forty-eight Korean men and women were recruited from a University campus and split evenly into four groups: male non-obese, male pre-obese, female non-obese, and female pre-obese. They were between the ages of 20-29 years (avg. 22-years), with the non-obese subjects having a BMI between 18.5-23 kg/m2 (avg. 22), and the pre-obese subjects have a BMI greater than 25 kg/m2 (avg. 29). Interestingly, the “pre-obese” or overweight persons are classified as obese when using the reference for Asians rather than the International Obesity Task Force. Body fat was also estimated using bioelectrical impedance, which put non-obese and pre-obese males at 20% and 30% body fat, respectively, and put non-obese and pre-obese females at 29% and 39% body fat, respectively.
A small portion (152g) of boiled rice was served with 200mL of water and provided to each participant between 7am and 7:30am after a 12-hour overnight fast. They were asked to eat it as they normally would, and measures of hunger and satiety were collected immediately before and after test food intake using paper-based visual analogue scales (pVAS). Additionally, subjective control of dietary behaviors was assessed by the Three-factor Eating Questionnaire (TFEQ). The EMG was used to determine
- Bite size (g): the amount of food per bite;
- Eating rate (g ingested/min): the weight of the test food ingested in 1 min;
- Chewing power (μV): the muscular activity summed from the left and right channels of the EMG during jaw closing and jaw opening to consume the test food;
- Chews per gram (chews/g): the number of chewing cycles per gram of test food;
- Total number of chews (TNC): the sum of chewing cycles to finish the test food;
- Meal duration (min): the duration of whole chewing sequences to consume the test food;
- Chews per mouthful (CPM): the number of chewing cycles made with a bite of test food until the bolus was completely ingested; and
- Chewing time per mouthful (CTPM): the duration of chewing with a bite of the test food until the bolus was completely ingested.
Regardless of weight-status, relative to the women, men had significantly greater bite size (20%), chewing power (double), and eating rate (45-55%), but significantly lower chews per gram (26-34%), TNC (20-35%), CTPM (11-18%), and meal duration (24-34%). Non-obese males also had a significantly lower CPM (4%) than non-obese females, and there were no differences in chewing speed between genders or weight-status.
Regarding the TFEQ, things were switched, with females having significantly higher results in all three domains relative to males. In fact, females’ demonstrated restraint scores 26% higher than males, disinhibition scores 67% higher, and hunger sensitivity 21% greater. Pre-obese participants in general also had significantly higher ratings of disinhibition than their non-obese counterparts, and in males only there was a significant positive correlation between the disinhibition score and eating rate. In non-obese persons, bite size and chewing power were significantly negatively associated with disinhibition, and the association with chewing power was present in pre-obese persons as well. Interestingly, there was no significant correlations between chewing performance parameters and eating behaviors in females.
I’m sure you are wonder what the hell disinhibition is. Basically, it is the susceptibility of eating in response to emotional factors and sensory cues. The current study clearly shows higher rates of disinhibited eating in pre-obese participants than in non-obese participants, as well as higher rates of cognitive restraint and hunger sensitivity. This was also true for females compared to males. It is interesting to note that individuals with disinhibited eating and cognitive restraint tend to restrict food in some situations, but grossly overeat in others. More interesting perhaps, was that only in males did disinhibition correlate positively to eating rate, which may possibly be explained, at least in part, by the fact that slower eating rate and prolonged chewing modulate impulse control.
The majority of differences were between genders however. The results of this study clearly showed that females take smaller bites and chew thoroughly with a weaker chewing power than males, while they consume the same amount of food. However, although not significant between weight-status, there were indeed differences in eating rate, chews per gram, TNC, CTPM, and meal duration by about 10% between pre-obese and non-obese persons. Thus, it could be that the small sample size limited the statistical power of the study to detect these differences. Sure enough, other studies using college students similar in age to the current subjects found that eating rate increased as obesity and body size increased.
So what can we take away?
This study definitely supports the notion that women and pre-obese (overweight) persons have a more emotional relationship with their food than their male or non-obese counterparts. Additionally, there are clear differences between males and females in terms of chewing performance, with possible differences between pre-obese and non-obese persons as well – but this would need to be confirmed in future studies.
The one real caveat that puts a damper on the generalizability, however, is a cultural thing. Yes, the age and ethnicity play a role as well, but the authors point out that Korean men perform compulsory military service for 18-20 months during which they are trained to eat quickly. Thus, the differences between males and females could simply a result of learned eating behaviors, and thus should be addressed in the future in other populations.