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Perceived Chewing Ability and Intake of Fruit and Vegetables2 School of Dental Sciences, Newcastle University, Framlington Place, Newcastle upon Tyne, NE2 4BW, UK Correspondence: * corresponding author, jane.bradbury{at}sheffield.ac.uk
Edentulous individuals have reduced chewing ability and lower fruit and vegetable consumption compared with dentate individuals. It has been suggested that the two are causally related. However, psychosocial factors such as attitude, self-identity, and knowledge of recommendations are predictive of intake in non-edentulous persons. The aims of this study were to: determine if perceived chewing ability was predictive of fruit and vegetable intake; explore the predictive ability of knowledge, attitude, and self-identity; and compare intake between edentulous and dentate individuals. Full denture-wearing (N = 79) and dentate persons (N = 52) completed a three-day food diary. Perceived chewing ability, sociodemographic, and psychosocial factors were assessed via self-administered questionnaire. The dentate persons consumed significantly more fruit and vegetables, but differences were not significant when juices were excluded. Perceived chewing ability explained ~ 4% variance in intake. Attitude, self-identity, and knowledge explained a further ~ 20%. If the diet of denture-wearers is to be improved, psychosocial factors, as well as perceived chewing ability, must be addressed.
Key Words: fruit and vegetables • perceived chewing ability • self-identity • nutrition knowledge • attitude
There is strong evidence that a diet high in fruit and vegetables protects against obesity, diabetes, cardiovascular disease, and some cancers, and the World Health Organization recommends an intake of > 400 g/day (WHO, 2003). Comparisons between edentulous and dentate individuals generally demonstrate that the edentulous have a lower intake (Johansson et al., 1994; Joshipura et al., 1996; Hung et al., 2005), although the difference is relatively small. Full-denture-wearers have lower objectively and subjectively measured chewing ability compared with dentate individuals (Boretti et al., 1995). The edentulous report that their food choice is affected because they wear dentures (Demers et al., 1996; Steele et al., 1998). A causal relationship between perceived chewing ability and fruit and vegetable intake would therefore seem plausible.
Surprisingly few studies have tested this hypothesis. Canadian older adults (N = 361) with lower perceived chewing satisfaction were less likely to choose raw fruit and vegetables and whole apples, but not cooked vegetables, canned fruit, and peeled apples (Rusen et al., 1993). In an American study (N = 731), although masticatory performance and bite force were significantly higher in the group with Lower fruit and vegetable intake is associated with sociodemographic and behavioral factors, such as being male, younger age, less education, lower income, manual occupation, living alone, smoking, higher alcohol consumption, and less physical activity (Billson et al., 1999; Thompson et al., 1999; Wallström et al., 2000). Many of these factors are also associated with edentulism (Joshipura et al., 1996; Kelly et al., 2000). Several psychosocial factors are associated with higher fruit and vegetable consumption, including knowledge of recommended intake (Havas et al., 1998; Wardle et al., 2000), a positive attitude (Dittus et al., 1995; Havas et al., 1998; Thompson et al., 1999), and self-identity (Sparks and Shepherd, 1992; Åstrøm and Rise, 2001). Self-identities are derived from individuals’ knowledge of the roles they occupy or their memberships in particular social categories. Individuals who strongly identify with the role of ‘healthy eater’ may therefore be motivated to act in accordance with their self-concept and to eat more healthily (Åstrøm and Rise, 2001). The aims of this study were to determine if perceived chewing ability was associated with fruit and vegetable intake, to explore the predictive ability of potential additional factors (knowledge, attitude, and self-identity), and to compare the intake of full-denture-wearing and dentate individuals. The hypotheses were that perceived chewing ability would not be predictive of fruit and vegetable intake, and that the addition of psychosocial factors would explain some of the variation in intake.
Participants Edentulous persons attending Newcastle Dental Hospital undergraduate clinics for replacement full conventional dentures, and dentate individuals attending student-hygienist or undergraduate restorative clinics were recruited between February, 2000, and July, 2001. Inclusion criteria were: edentulous  1 yr and wearing full dentures, or having 21 teeth and no denture; aged 45–80 yrs; community-dwelling; not insulin-dependent diabetic; and if non-insulin-dependent diabetic or on a cholesterol-lowering diet, diagnosed 6 mos. Ethical approval was obtained from the Local Research Ethics Committee, and all participants gave informed consent.
Procedure Food diaries and questionnaires were collected by the nutritionist at the subsequent appointment, when participants were interviewed to obtain recipes, probe for missing items, and determine portion sizes using food photographs (Nelson et al., 1997). ‘Fruit’ was defined as all fresh, frozen, canned, and dried fruit; ‘vegetables’ included all fresh, frozen, canned, and dried vegetables, including pulses (i.e., dried peas, beans, and lentils), but not potatoes (Williams, 1995); and ‘juices’ included all pure fruit and vegetable juices. Participants’ height was measured to the nearest 0.5 cm, and weight, in light clothing, to the nearest 0.1 kg.
Evaluation Measures
Perceived Chewing Ability
Attitude, Self-identity, and Knowledge of Recommendation
Statistical Analysis
Of 266 individuals initially approached (160 with dentures, 106 dentate), 153 (57.5%) met the inclusion criteria (95 with dentures, 58 dentate). Two denture-wearers were subsequently excluded for medical reasons; one denture-wearing and five dentate persons withdrew. Fourteen persons (13 with dentures, one dentate) were not given the full questionnaire and are excluded from this analysis, thus leaving 131 persons [79 with dentures (52 women), 52 dentate (27 women)] who completed all aspects of the study. Those individuals withdrawing did not differ on age or sex.
The mean (SD, range) time of complete denture use was 29.8 yrs (15.0 yrs, 1–57 yrs). The denture-wearers were older than the dentate [66.8 yrs (7.2 yrs, 45–79 yrs) vs. 58.6 yrs (7.9 yrs, 46–80 yrs), p < 0.0005], and were more likely to be retired and to have a lower income and lower educational attainment (Table 1
Fruit and Vegetable Intake Both groups showed a wide range of fruit and vegetable intake: denture-wearers, 22-1637 g/day; and dentate, 73-1304 g/day. The denture-wearers were less likely to consume juice (19% vs. 40%, p = 0.007) and fruit (78% vs. 90%, p = 0.075). Only intakes of fruit including juices, and fruit and vegetables including juices, were significantly different (Table 2  ).
Perceived Chewing Ability Those rating their health as ‘poor/very poor’ compared with ‘good/very good’ had lower perceived chewing ability (p = 0.020). There was also a difference by age (p = 0.036), with the oldest (73–80 yrs) having lower ability than the youngest (45–52 yrs) age group (p = 0.041), but there was no interaction effect between age and health (p = 0.142). The difference in perceived chewing ability between denture-wearing and dentate participants [14.08 (4.79, 3–21) vs. 7.15 (4.28, 3–20)] remained significant after adjustment for age and health (p < 0.0005).
Partial correlations between reported avoidance of ‘problem’ foods, perceived chewing ability, and fruit and vegetable intake showed that the score for chewing ability was positively associated with reported avoidance of most items for the denture-wearers, but only with apples for the dentate. Actual intake of fruit and vegetables was not associated with avoidance in the denture-wearers (Table 3
Psychosocial Factors There were no significant differences for attitude [dentures 15.89 (3.26) vs. dentate 16.62 (3.83); p = 0.245] or self-identity [dentures 10.45 (2.28) vs. dentate 10.62 (2.10); p = 0.674]. Fifty percent of the dentate individuals were aware of the fruit and vegetable recommendation, compared with 34% of the denture-wearers (Table 1  ).
Predictors of Fruit and Vegetable Intake
Contrary to our hypothesis, and unlike previous research (Shinkai et al., 2001, 2002), this study found a significant relationship between fruit and vegetable intake and perceived chewing ability. Self-assessed and dentist-assessed chewing ability tends to be weakly correlated (Feine and Lund, 2006). Perceived chewing ability is likely to have a greater impact on food choice, and Feine and Lund contended that patient-based evaluations are more valid (2006). Combining data from the two groups allowed us to explore the effect of perceived chewing ability rather than of dental status, and permitted the inclusion in the analysis of dentate individuals with low perceived chewing ability, the effect of whom would probably not have been apparent had the groups been examined separately. Additionally, use of a scale rather than dichotomous variables enabled a range of abilities to be captured. Although perceived chewing ability was associated with fruit and vegetable intake, the impact was modest: This may help to explain the limited impact of improvement in chewing ability on dietary intake (Sebring et al., 1995; Hamada et al., 2001; Morais et al., 2003; Allen, 2005) in the absence of an associated dietary intervention (Bradbury et al., 2006), although there may be an improvement in nutritional status (Morais et al., 2003). Attitude, self-identity, and knowledge of recommended intake were considerably more predictive of intake, explaining around 20% of the variance. Previous studies have shown that a positive attitude is associated with a higher fruit and vegetable intake (Dittus et al., 1995; Havas et al., 1998; Thompson et al., 1999). Self-identity has been shown to be predictive of intention to eat fruit and vegetables (Sparks and Shepherd, 1992; Åstrøm and Rise, 2001); this study has shown that self-identity is also predictive of behavior. Knowledge of recommended fruit and vegetable intake is associated with higher consumption (Havas et al., 1998; Wardle et al., 2000); it is of concern that so few participants could correctly identify the recommendation. The finding of no difference between the dentate and denture-wearing groups in fruit and vegetable intake when juices were excluded from the analysis should be treated with some caution due to the small sample sizes. However, the magnitudes and patterns of differences are consistent with those found in comparable larger studies (Johansson et al., 1994; Greksa et al., 1995; Joshipura et al., 1996; Hung et al., 2005). Reported avoidance of hard and difficult-to-chew foods was correlated with perceived chewing ability in the denture-wearers, but not with total fruit and vegetable intake. This supports the use of reported avoidance of certain foods as a method of measuring impaired chewing ability, but it should not be assumed that avoidance necessarily translates into an inadequate diet. Some fresh fruits and raw vegetables are difficult for denture-wearers to eat, but these problems can be overcome with food preparation (Rusen et al., 1993; Hung et al., 2005). Additionally, if the diet of the general population is relatively processed, the avoidance of hard foods by denture-wearers will not manifest as a difference in intake. It would be interesting to explore the effect of chewing ability on intake in countries with different food cultures. As with similar studies, the cross-sectional nature of the data is a limitation. Without longitudinal studies, it is impossible to determine whether the dietary intake of edentulous individuals reflects intake prior to tooth loss or is in response to tooth loss, or whether dental status is a marker for a clustering of health behaviors associated with a less healthful diet. Edentulous individuals and those with low fruit and vegetable intakes have many sociodemographic and behavioral factors in common. It would, perhaps, be surprising if the edentulous did not have a lower intake. Perceived chewing ability explained approximately 4% of the variance in fruit and vegetable intake. In contrast, psychosocial factors, particularly the presence of a positive attitude, had a much greater impact. Improving perceived chewing ability through prosthetic rehabilitation, although important, may not improve fruit and vegetable intake in the absence of contemporaneous intervention to address psychosocial factors.
This study was funded by Newcastle University Bradlaw Studentship and Small Grants Fund. The assistance of the participants, hospital staff, and students is gratefully acknowledged. This paper is based on a thesis submitted to the School of Dental Sciences, Newcastle University, in partial fulfillment of the requirements for the PhD degree; a preliminary report was presented at the 81st General Session of the International Association for Dental Research (June 25–28, 2003) and published in the Journal of Dental Research 82(Spec Iss B):2050.
1 Present addresses, Department of Oral Health and Development, School of Clinical Dentistry, University of Sheffield, Claremont Crescent, Sheffield S10 2TA, UK 
3 Age Concern North Tyneside, 13 Saville Street West, North Shields NE29 6QB, UK and
4 Department of Restorative Dentistry, Cork University Dental School & Hospital, Wilton, Cork, Ireland Received for publication March 31, 2006. Revision received March 18, 2008. Accepted for publication April 11, 2008.
Journal of Dental Research, Vol. 87, No. 8,
720-725 (2008) This article has been cited by other articles:
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ABSTRACT
INTRODUCTION
= 0.916) were summed to calculate a perceived chewing ability score: A higher score indicated lower perceived chewing ability. Participants were also asked whether they avoided 12 foods identified from the literature as likely to cause problems (
