Health Education Research, Vol. 15, No. 4, 449-462,
August 2000
© 2000 Oxford University Press
Tailoring dietary feedback to reduce fat intake: an intervention at the family level
University of Ghent, Faculty of Medicine and Health Sciences, Department of Movement and Sport Science, Watersportlaan 2, 9000 Ghent, Belgium and
1 Department of Health Education and Promotion, Universiteit Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands
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Abstract |
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In this study, we wished to investigate whether the use of tailored nutrition education letters addressed to each family member simultaneously at home could serve as a valuable strategy for nutrition education. Family quartets (both parents and two adolescents, all healthy individuals) were chosen to be the units of intervention. The first aim of our study was to investigate the impact of tailored versus standardized nutrition education on fat intake and on psychosocial determinants of fat intake in families, using a randomized dietary feedback study. Our second aim was to study the differential effect of the tailored nutrition education on different family members. Analyses were conducted among 18 experimental families (n = 72) and 17 control families (n = 68). The tailored intervention was more effective than the non-tailored intervention in reducing total and saturated fat intake when all the family members were included (F = 4.0, P < 0.05 and F = 5.9, P < 0.05). However, follow-up analyses revealed that only mothers benefit from the tailored intervention (F = 6.4, P < 0.05 and F = 10.2, P < 0.005). For fathers and adolescents, both interventions resulted in a significant decrease in fat scores. Furthermore, tailored feedback resulted in stronger awareness of personal fat intake and awareness of fat intake of family members. Tailored advice has the potential to communicate the personal need to change. As differences in fat reduction between family members receiving general or tailored nutrition education letters were smaller than expected, future research will have to prove that family-based tailored interventions are more effective than standardized interventions and interventions focusing on a single person. It also needs to be clarified why mothers in particular benefit from tailored feedback.
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Introduction |
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There is a consensus that dietary change interventions are a necessary component of health promotion programmes to prevent cardiovascular diseases and cancer (Glanz, 1988
; Kris-Etherton et al., 1988; Heimendinger et al., 1990; Potter et al., 1990; World Health Organization, 1990; Gordon et al., 1991). Within a healthy diet, reducing fat intake and increasing fruit/vegetable consumption play an important role. Individualized, or tailored, nutrition education interventions have been shown to be effective in inducing dietary change (Brug et al., 1996, 1999). The present study investigates the impact of tailored nutrition education materials at the family level. First, the rationale for family-based tailoring will be briefly described, then the evidence for the effectiveness of tailoring health education is reviewed, after which the design, methods and results of the present study will be described and discussed.
Epidemiological evidence exists for the relationship between fat intake and the prevention of cardiovascular disease. Total (saturated) fat intake or energy percent from fat or from saturated fat and hypercholesterolemia have been found to be associated with arteriosclerosis and morbidity and mortality related to cardiovascular diseases (Willet, 1994; Ascherio et al., 1996). Dietary guidelines in most Western countries including Belgium recommend reducing fat intake to 30–35% or less of the energy intake (US Department of Agriculture/US Department of Health and Human Services, 1985; Hulshof et al., 1993; Voedingsaanbevelingen voor België, 1996). Despite the general awareness among the population of the risks associated with a high-fat diet, the prevalence of high-fat intake is still very high. In Belgium, 60–70% of the adult population consume more than 35% energy from fat, while only 11–16% meet the guideline of 30% energy from fat (De Bourdeaudhuij and Van Oost, submitted). In Belgium, as in other countries, mean energy percentages of fat between 38 and 40% were found (Kant et al., 1995; De Bourdeaudhuij and Van Oost, submitted). High-fat intake is prevalent in all age groups, socio-economic groups and in both sexes (Hupkens et al., 1997). Hence, it is not possible to identify specific target groups based on traditional segmentation variables. As a consequence, it is necessary to focus on large numbers of people in which five vehicles can be used: schools, work sites, community agencies, medical care facilities and media (Kolbe, 1988). However, most nutrition intervention studies do not report large effects on behavior change and suggest that maintaining long-term change is difficult to achieve (Hollis et al., 1984; Zimmerman and Connor, 1989; Backett, 1992).
Fat reduction interventions may become more effective when these interventions are tailored to relevant individual characteristics of the people in the target population and when the family context is taken into account.
Traditionally, behavior change was the realm of psychologists, mostly experts trained in the field of psychopathology. In psychotherapy, therapists match their interventions maximally to the needs of the client (Velicer et al., 1993; Roth and Fonagy, 1996). Interventions are adapted to the individual's diagnostic, behavioral and motivational characteristics. In the field of health psychology, tailoring interventions to the individual is specifically used in secondary and tertiary prevention, e.g. in order to try to help patients suffering from hypercholesterolemia or recovering from a heart attack to change their activity patterns, food choices or smoking habits (Butowski and Winder, 1998; Willett, 1998). In primary prevention and health education, efforts have been made only recently to tailor interventions to individual's characteristics. Because large numbers of people are often involved in primary prevention, a skip was made from group or individual face-to-face education to written education. In the past few years, tailoring has been used especially in smoking cessation interventions (Strecher, 1999) but also for dietary change (Brug et al., 1996, 1999). The use of powerful computers which can match answers on a questionnaire to specific interventions enables health educators to reach large groups of people in which the human-guided intervention is combined with a maximal cost-effectiveness (Velicer et al., 1993). Recently, eight studies on tailored nutrition interventions for primary prevention of chronic disease have been reviewed (Brug et al., 1999). The authors concluded that tailored nutrition interventions were generally more effective and better appreciated than general nutrition education, especially for fat reduction. The authors further argued that personalization of fat reduction education was especially useful, since many people are not aware of their high-fat intake. Moreover, there are many different misconceptions about low-fat alternatives to high-fat choices.
Until now, tailored nutrition interventions have only focused on individuals (Brug et al., 1996, 1999). However, it has been argued that dietary behaviors are especially well suited to family-based interventions because meals often involve the entire family (Nader et al., 1989, 1992). In the past, family-based interventions were often translated into an intervention directed at the mother. She was assumed to have the strongest impact on the dietary behavior of all family members. Some researchers, however, stressed the importance of the influence exerted by other family members, both the husband and the children (Eppright, 1969; Kerr and Charles, 1986; Newson and Newson, 1990; Mennell et al., 1992). Several studies were conducted in Belgium to obtain an insight into the ability of each family member to influence food consumption patterns. Major implications for nutrition education were that targeting only the gatekeeper (mother) is counterproductive, that one member of the family is seldom strong enough to influence family food choices and that nutrition education interventions could be expected to be more successful if several family members decide to change their eating behavior in a more healthy way at the same time (De Bourdeaudhuij and Van Oost, 1997, 1998a,b; De Bourdeaudhuij et al., 1997a,b). From this it can be argued that efforts have to be undertaken to construct effective and feasible nutrition education interventions directed at whole families. However, it is clear that developing nutrition education programmes involving entire families is not easy. Previous efforts experienced significant problems such as high non-attendance rates, drop-out and difficulty with recruitment (Perry et al., 1987; Baranowski et al., 1990). In this study, we wished to investigate whether the use of tailored nutrition education letters directed at each family member simultaneously at home could serve as a valuable strategy for nutrition education. Family quartets (both parents and two adolescents) were chosen as the units of intervention. The first aim of our study was to investigate the impact of tailored versus standardized nutrition education to reduce fat intake in families, using a randomized dietary feedback study. As there are strong indications that health behavior is primarily a result of behavioral intention, which in turn is predicted by three main psychosocial factors, i.e. attitudes, social influences and self-efficacy expectations or perceived behavioral control (De Vries et al., 1988; Ajzen, 1991; Conner and Norman, 1996), differences in changes in psychosocial determinants of fat intake between both conditions were also studied. Our second aim was to study the differential effect of the tailored nutrition education on different family members.
It was expected that subjects in experimental families would appreciate their intervention material better and that they would experience stronger subjective effects of the intervention they received. It was further expected that subjects within the experimental families would have a stronger decrease in fat intake levels and an increase in positive determinants towards fat reduction after the intervention when compared to subjects in the control families. We further hypothesized that the tailored nutrition education would have equal effects on each family member.
We believe that this study is of special importance in the field of health education research as it may possibly provide us with a feasible and effective strategy for implementing nutrition education at the family level.
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Methods |
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Sample and procedure
A random sample of two-parent families with at least two adolescents (aged between 12 and 18) living at home was drawn from Ghent, a mid-sized town in Belgium. Families were contacted by telephone and asked to come to the laboratory to participate in a study on food choices. Because of the inclusion criterion that four members of each family had to participate, the response rate was low (10%). The main reasons for non-participation reported by subjects were (1) organizational problems, as we asked for the four family members to attend the laboratory together at the same time, and (2) refusal to participate by one or more family members (especially fathers and adolescents).
Nevertheless, 40 families (n = 160) agreed to participate and were randomly assigned to an experimental or control intervention. At baseline, each participant received a questionnaire designed to obtain information on the psychosocial determinants of fat intake together with a food-frequency questionnaire to measure energy percentages of fat. As all subjects completed the questionnaires at the laboratory, with a research assistant present, we thus checked for the bias often found in family research in that several questionnaires are filled in by the same person (De Bourdeaudhuij and Van Oost, 1998a).
Two weeks later, all members of the families in the experimental condition were mailed nutrition education letters at their home addresses, tailored to personal fat intake levels, motivation to reduce fat intake, awareness of personal fat intake, and attitudes and self-efficacy expectations related to fat reduction. Feedback letters were not computer-tailored, but tailored manually. All members of the families in the control condition received (identical) general nutrition education letters which were also addressed to them personally. Four weeks after the subjects had received their feedback letters, they were asked to attend the laboratory again to complete the post-test questionnaires. Two families from the experimental group and three families from the control group dropped out, mainly because all four family members were not willing to come to the laboratory a second time. All analyses were conducted among the 18 experimental families (n = 72) and 17 control families (n = 68), representing 87.5% of the subjects who completed the baseline screening.
Questionnaires
The measures for the independent variables were derived from Brug et al. (Brug et al., 1997), based on Operant and Social Learning Theories (Bandura, 1986), and on social-psychological theories such as the Theory of Planned Behavior (Ajzen and Madden, 1986) including attitudes, social influences and self-efficacy expectations. On the basis of research on determinants of motivation to reduce fat consumption (Brug et al., 1994), awareness of personal intake was also included as a determinant. Moreover, awareness of other family members' and friends' fat intake was included as the present intervention at the family level was supposed to have a broader impact than an individual intervention (see Intervention for more information).
Attitudes were assessed by asking respondents to what degree they thought that eating fat is bad or good, unpleasant or pleasant, and nasty or tasty (three items; Cronbach's 
= 0.80). Perceived social support was measured by asking respondents to what degree they expected social support from family members and from friends if they tried to eat less fat (two items; Cronbach's = 0.79). Self-efficacy was measured by asking respondents how difficult or easy they thought it was and how confident they were of being able to eat less fat in certain difficult situations (having a lot of work, being alone, having to buy other products, really wanting to) (five items; Cronbach's = 0.83). Self-assessed fat intake (awareness) was measured by asking respondents to evaluate their fat intake, and by comparing this intake with people of their age and sex (two items; Cronbach's = 0.79). Fat intake of significant others was assessed in the same way as the self-assessment for family members (two items; Cronbach's = 0.76) and for friends (two items; Cronbach's = 0.66). One question was included to measure the subjects' intentions to eat a low-fat diet. Attitudes were measured in relation to `eating fat', whereas `eating less fat' was used as target behavior in all the other items, except for intentions, where `a low-fat diet' was used. This inconsistency in item construction may, for example, lead to an overestimation of positive intentions towards eating a low-fat diet because many people are convinced that they already eat a low-fat diet. All previous items were measured on seven-point scales.
In the post-test questionnaire the same variables were assessed. In addition, the participants were asked about their reactions to the nutrition information letter that they received and whether the nutrition information letter had resulted in changes in opinions about their diets, in their intentions and in their dietary behavior (see Table I for items).
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To assess eating patterns, registered dieticians adapted a 56-item food-frequency questionnaire validated in the Netherlands (Feunekes et al., 1993
) for our Flemish population. Some minor changes were made, adding some typical Flemish food. Respondents could choose whether to report the frequency of consumption of each food item per day, per week or per month with a reference period of the past 4 weeks. From this food-frequency questionnaire, intake of total fat, saturated fat, monounsaturated fat and polyunsaturated fat was computed in grams and as a percentage of total energy intake. For this purpose, a computer program was written by Aben et al. (Aben et al., 1993), in which frequency of consumption for each food item was first calculated per week and then multiplied by a weighted fat factor based on the fat content of food items as reported in the NEVO tables in the Netherlands (Stichting Nederlands Voedingsbestand, 1987). Standardized portion sizes were used in computing fat scores. The validity and reliability of this adapted food-frequency questionnaire were investigated in a small sample of students (n = 45 for validity, n = 90 for reliability). Pearson's product-moment correlation coefficient used to evaluate the linear association between the results of the food frequency questionnaire and a 7-day food diary showed appropriate validity (r = 0.78). Further, test–retest reliability using an interval of 2 weeks showed a Cronbach's coefficient of 0.83 on total fat intake.
Intervention
The intervention was mainly targeted at reducing fat intake. Subjects in the experimental condition received a feedback letter including messages based on their answers to the screening questions. The tailoring procedure developed by Brug et al. (Brug et al., 1998) was followed and the messages included in the Brug et al. (Brug et al., 1998) computer program were used. However, in the present study the letters were constructed manually. The original Brug et al. (Brug et al., 1998) computer program was based on a different food-frequency questionnaire which is less suitable for use among a Flemish population and has not been validated among adolescents. No computer program was written for the present study since we first wanted to establish the potential of family-based tailoring before making this investment. Respondents received feedback about their fat intake as well as about their attitudes, perceived support and self-efficacy in relation to fat reduction. The feedback messages about fat intake included respondents' actual fat consumption expressed in percent of energy from fat, a comparison of this percentage with the Flemish recommendations (preferably 30% and not more than 35% energy from fat) and with the mean scores of the other adolescents, mothers or fathers participating in this study. The messages also included the comparison between the actual consumption and the way in which participants rated their own consumption. A figure was included to visualize personal fat intake levels as compared to the recommendation as well as to the mean fat intake of comparable others (adolescents, mothers or fathers). Further messages were included which addressed different important dietary fat sources in the Flemish diet, for which low-fat alternatives to high-fat choices were suggested.
Further, for respondents with low self-efficacy expectations, suggestions were given on how to deal with high-risk situations such as the presence of high-fat foods in the home (avoiding such situations by making low-fat shopping lists), being alone (suggestions on low-fat alternatives for meals for one) and lack of time for food preparation (recipes for easy to cook low-fat alternatives). Finally, all subjects who reported a positive intention to reduce their fat intake were advised to convert these plans into direct action in the week(s) to come, preferably in the next week. No attempts were made to stimulate positive family influence, e.g. by including recommendations to share the results with other family members.
Subjects in the control condition received a general nutrition education letter (Brug et al., 1998). This letter included information about the importance of a healthy diet, and gave general information about dietary fat reduction, the health risks of a high-fat diet were stressed, the mean population intake (40% energy) was compared with the recommendations (30% energy), and further information was given about reducing fat in milk and dairy products, butter, meat, sauce, snacks, sweets and chocolate.
Analyses
In order to assess possible response bias, t-tests were carried out to look at differences in mean fat scores between subjects within families who dropped out and subjects who completed the baseline and the post-test questionnaires. 
2 tests and t-tests were conducted to study differences in family members' reactions to the feedback letters for the tailored and the non-tailored groups. Repeated measures MANOVAs were used to test for significant changes over time in fat intake and determinants between the tailored and non-tailored groups. Time was used as a within-subjects variable, condition as a between-subjects variable.
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Results |
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Dropout analysis
A significant difference was found between dropouts (mean = 16.0%) and the research sample (mean = 14.3%) for intake of monounsaturated fats [t(158) = 2.29, P < 0.05] at baseline, with a higher intake among dropouts. No differences were found for total fat [t(158) = 1.14, NS], saturated fat [t(158) = 0.15, NS] and polyunsaturated fat [t(158) = 0.57, NS].
Participants' reactions to the tailored letters
Table I
shows the respondents' reactions to the feedback letters. Both groups rated the information in their feedback letters as interesting and comprehensible, with mean scores between +1 and +2 on a seven-point scale from –3 (very low) to +3 (very high). Respondents in the experimental condition thought that the letters were more personally relevant (mean = +0.9 in experimental and mean = +0.2 in control condition) and contained more information that was new to them (mean = +0.6 in experimental and mean = –0.1 in control condition). However, the subjects who received the general feedback reported that they gave more credence to the letters (mean = +1.6) than the subjects in the tailored feedback group (mean = +1.2). Further, a significant difference of about 15% was found between the two groups in reading and keeping the letter, in favor of the experimental condition. The majority of the subjects in the experimental group discussed the letter with others (80%), compared to only 46% of the subjects in the control group. Finally, 69% of the subjects who received the tailored intervention reported that they changed their opinion about their diet and intended to change their diet in the future, compared with 32% in the control group. Differences in reported behavior change are somewhat smaller though still significant, with 46% of the subjects in the tailored feedback condition reporting that they had changed their diet, compared with one-quarter in the general feedback condition.
Differences in impact between baseline and post-test for fat intake
Table II shows the results of the repeated measures MANOVA for total fat, saturated fat, monounsaturated fat and polyunsaturated fat. The analyses of variance for total fat and saturated fat showed a significant time effect and a significant interaction effect for all family members together. The time effect reports a significant decrease in total and saturated fat scores for both conditions. The significant interaction between time and condition shows that the decrease in energy from total fat and energy from saturated fat in the tailored feedback group was significantly larger in the experimental condition compared to the general feedback group. Tuckey post hoc tests do not reach significance for differences between family members. However, analyzing these effects separately for mothers, fathers and adolescents shows that the significant interaction between time and condition only applies to mothers, which suggests that only mothers benefit from the tailored intervention. This significant interaction effect may be partly due to the mean total fat scores increasing between baseline and post-test for mothers in the control condition. For fathers and adolescents, only significant time effects were found. This means that both the tailored and the general feedback intervention is effective in reducing energy percentages of total and saturated fat in fathers and adolescents. Fat reduction in the experimental condition was also greater for fathers and adolescents, but a lack of sufficient statistical power may have been responsible for the absence of a significant interaction effect. A similar pattern was found for monounsaturated fat, with the exception that no overall significant interaction effect was found between time and condition. No significant effects were found for polyunsaturated fat.
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Differences in impact of interventions on determinants of fat intake
Table III
shows the results of the repeated measures MANOVA for the determinants of fat intake included in our study as well as for the different fat intake perception scales.
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In general, only a few significant effects were found. Significant differences between the tailored and general feedback group (interaction effects) were present for all family members for perceptions of personal fat intake (awareness) and for parents for perceptions of fat intake levels of family members (family perception). The significant interaction effect shows that subjects who received the tailored intervention evaluated their fat intake as higher at post-test than subjects who did not receive information about their own fat intake. As only 10 subjects (two adolescents, three fathers and five mothers, or 7% of the total population) were told that their fat intake was in agreement with the recommendations, it is a positive result that subjects rate their fat intake higher at post-test, which means that in general subjects were more aware of their own fat intake. A significant interaction effect for the perception of friends' fat intake was only found for adolescents.
A significant time effect was found for intention in relation to dietary change. Further, a significant interaction effect was found for attitudes towards fat intake, but in the opposite direction. Subjects, but especially parents, in the tailored feedback group show more positive attitudes towards eating fat over time (or less positive attitudes towards the target behavior), in contrast to parents in the general feedback group who report an increase in negative attitudes towards eating fat. No significant interaction effect was found for self-efficacy. The condition effect found for parents is due to lower baseline self-efficacy scores for parents in the tailored feedback condition. The condition effect found for family perception shows higher scores on family perception of fat intake in the experimental condition. No significant effects were found for social support.
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Discussion |
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The aim of the present study was to determine whether tailored information would result in a greater reduction in fat intake in families than non-tailored information. The data showed that the tailored intervention was more effective than the non-tailored intervention in reducing total and saturated fat intake when all family members were included. However, follow-up analyses of individual family members revealed that only mothers benefit from the tailored intervention. For fathers and adolescents, both the tailored and non-tailored intervention resulted in a significant decrease in total and saturated fat scores. In a recent review of the literature, Brug et al. (Brug et al., 1999
) reported evidence for an additional impact on fat reduction of tailored feedback as compared to general nutrition information. The present study provides evidence that the impact differs between family members.
The program evaluation data show that respondents who received tailored feedback more often read the letter completely, kept it, discussed it with others and perceived the information to be more personally relevant and new. This is in line with earlier findings on tailored feedback. Better appreciation and use is a prerequisite for a higher impact of these materials. Further, also in line with earlier studies, respondents judged tailored feedback to be less credible, probably because of the discrepancy between their self-assessed fat intake and their actual fat score reported in the letters (Brug et al., 1998). These findings suggest that, as expected (Campbell et al., 1994; Skinner et al., 1994; Brug et al., 1998), our tailored intervention led to more attention, involvement and cognitive processing than the non-tailored intervention.
Tailored feedback resulted in stronger awareness of personal fat intake and of fat intake of family members. Since awareness of personal risk behavior has been identified as an important prerequisite for behavior change motivation (Weinstein, 1988), we consider that the tailoring effect on awareness also points to the conclusion that family-based tailored fat feedback is superior to general information about fat reduction.
The fact that a higher tailoring impact was found among mothers may have several explanations. First, mothers often have a special position within the family unit with regard to food. Mothers are often seen as `gatekeepers' controlling the food, being responsible for menu-planning, shopping and cooking (Sallis and Nader, 1988; Pill and Parry, 1989). Previous studies found that mothers are highly motivated to eat less fat, they have the intention to cook and eat a low-fat diet, they have most knowledge about the fat content of foods, they have most positive attitudes, but they are not able to succeed in changing their children's and husband's food habits on their own (Backett, 1992; Andersen et al., 1995; De Bourdeaudhuij and Van Oost, 1998b). A recent study indeed showed that tailored fat feedback is especially effective among people who are already motivated to change (Brug and Van Assema, 1999).
Secondly, the general nutrition education letter used in our research also included a large amount of information on fat content, fat standards, mean population intake and health risks, and provided subjects with low-fat alternatives to high-fat food choices. Moreover, these general information letters were addressed to the family members personally. It could be that the difference between the two interventions was not large enough for subjects with less interest in and less knowledge of nutrition at baseline (i.e. the fathers and adolescents in the sample).
Previous studies showed the potential of multiple tailored interventions. In these interventions subjects receive more than one tailored letter in which further recommendations for behavior change are made within a time span of one to several months. Even if the letters in the multiple tailored condition contained roughly the same information as the letters in the single tailoring condition, it was shown for nutrition as well as for other health behavior that the effect of multiple tailoring exceeded that of single tailored feedback letters (Brug et al., 1998; Dijkstra et al., 1999). It may be possible that multiple tailoring is needed to show an additional effect of tailoring on top of general nutrition information for fathers and adolescents. Another possibility is that the tailoring procedure must be made more comprehensive and detailed, focusing especially on family determinants of fat intake next to the individual determinants included in the present study. In previous research we found that general family characteristics such as family cohesion and adaptability, as well as more specific family interactions concerning food choices such as decision-making, communication and establishing food rules, have an important impact on health behavior and more specifically on food choice (De Bourdeaudhuij and Van Oost, 1998a,b). Modifying these family interactions might have a powerful effect in changing food habits. Including family-related messages in the tailored feedback letters could possibly influence these family interactions around food. Depending on the answers family members give to family-related questionnaires, guidelines could be given, e.g. to establish clear food rules within the family (e.g. French fries once a week, chocolate only at the weekend, etc.), to make shopping lists with all family members including at least 50% low-fat foods, to make agreements that each family member may choose a low-fat dish and that everybody would eat at least a part of it without complaining, etc. We are aware that including these family components in nutrition education will be very difficult, although we believe that this might be a way to improve family-based tailored diet feedback in the future.
Only a few significant effects were found on attitudes, perceived social influences and self-efficacy expectations towards a change in fat intake between and within study conditions. This may seem surprising as it is generally accepted that attitudes, social influences and self-efficacy are strong predictors of behavior and intention (De Vries et al., 1988). Part of this lack of effect may have been caused by the way the determinants were assessed in the questionnaire. Self-efficacy, for example, was questioned in relation to being able to eat less fat. If the intervention helped to increase self-efficacy, which in turn resulted in a lower fat intake at post-test, the perceived ability to further decrease fat intake at post-test could indeed be as low as the baseline level. Nevertheless, the intention to eat a low-fat diet had increased in the tailored as well as the non-tailored condition. This suggests that our intervention succeeded in decreasing fat intake and in increasing the intention to eat a low-fat diet without affecting the determinants of intention and behavior. This is not in line with the presumed uni-linearity of social cognitive models such as the Theory of Planned Behavior (Ajzen and Madden, 1986). We would expect that determinants change first, followed by changes in intention and behavior. In the past, numerous studies supported the Theory of Planned Behavior for food choice and dietary behavior, although mostly using cross-sectional data (Conner and Norman, 1996). Some authors argue that determinants are only rational considerations after behavior has occurred or changed instead of causal factors determining behavior (Bennett and Murphy, 1997). This may be one explanation for the results of the present study. Another explanation may lie in the fact that previous studies revealed that large proportions of populations have misconceptions about personal dietary intake levels (Lloyd et al., 1993; Brug et al., 1997; Lechner et al., 1998). It could be argued that this misconception of personal fat intake is important in several ways. First, people who think they already eat a low-fat diet will not make efforts to decrease their fat intake and they will consider nutrition education interventions not to be applicable to them. Secondly, it has been argued that among subjects who are unrealistic about their fat intake levels, determinants such as attitudes, social influences and self-efficacy are not associated with fat intake because these determinants reflect what people think they eat and not what they actually eat (Brug et al., 1994; Lechner et al., 1998). This could possibly be an additional explanation for the lack of intervention effects on determinants of fat intake we found in the present study.
There are several important limitations to note in interpreting this study. First, the response rate was low and it therefore remains uncertain whether the results can be generalized to the Belgian population of families as a whole. However, reported fat scores and intentions to change were comparable with population means. A selection bias still remains possible favoring families, e.g. with specific family interaction patterns. Secondly, the total sample size is low, mainly due to the difficulties in recruitment and to the only partly computerized tailoring procedure we used. In the future, the use of a completely computer-generated procedure will make it possible to study larger samples and to include comprehensive and detailed tailoring. With larger samples, analyses may also be executed at the family level, e.g. using a multi-level approach. The sample size might also be responsible for the lack of significant interaction effects in fathers and adolescents. The present study only investigated the short-term impact of the interventions. It therefore remains uncertain whether the effects found were sustained in the longer run. In the method section, an inconsistency in item construction was reported, in which attitudes were measured towards `eating fat', whereas `eating less fat' was used as target behavior in all other items, except for intentions where `a low-fat diet' was used. This inconsistency may, for example, lead to an overestimation of positive intentions towards eating a low-fat diet because many people are convinced they already eat a low-fat diet. This inconsistency could have been prevented. A further limitation of the present study is in the use of self-reports to assess tailoring effects (Brug et al., 1999). More objective criteria such as cholesterol levels or other blood parameters would give more verifiable results. Further, the present study did not provide information about possible additional effects of family-based tailoring to individually tailored fat feedback. Finally, it has to be noted that the total fat intake at baseline for the general feedback condition was substantially less than the total fat intake at baseline for the tailored feedback condition and is even less than the fat intake at post-test for the tailored feedback condition. As this difference was not significant, baseline fat intake levels were not included as a covariate in the analyses. However, we are aware that the effectiveness of tailored or standardized nutrition education is possibly dependent upon baseline fat intake level, which may have affected the results.
Despite these limitations, this study has several implications for nutrition education practice and research. An intervention aimed at fat reduction in which four family members simultaneously receive a single nutrition education letter at home has shown an impact on fat intake. However, differences in fat reduction between family members receiving general or tailored nutrition education letters were smaller than expected and only valid for mothers. It is possible that the `family effect' (several family members at a time) is stronger than the `tailoring effect'. However, it was not within the scope of this study to investigate the difference in impact between a family-based and individual-based intervention. Further research is needed, including both conditions: tailoring versus standardized nutrition education directed to a single family member versus more than one family member. Further research also has to clarify why mothers benefit from tailored feedback. In the future, it remains to be proven that tailored interventions at the family level are more effective than standardized interventions and than interventions focusing on a single person. If few differences remain between the two methods and the two units of intervention, the cheaper, more time-efficient and more feasible method would be the one to go for.
However, the tailoring effect on dietary fat awareness suggests that personal feedback on fat intake, together with personalized information about important fat sources and suggestions on how to cut back on fat, has considerable potential. The use of general information focusing on fat reduction and/or determinants of fat intake may run the risk of being ineffective, particularly because many individuals are convinced that the messages do not apply to them personally. They wrongly perceive their fat intake and that of their family members to be low already and therefore do not perceive any need to change. Tailored advice has the potential to communicate this personal need to change.
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Acknowledgments |
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The authors would like to thank Nathalie Stroobant, Bieke Byttebier and Gert Scheerder for their contribution in data gathering and tailoring feedback letters, and Paulette Van Oost for supervising the project. This study was financially supported by the University of Ghent and the Belgian Society against Cancer.
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References |
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Received on June 21, 1999; accepted on February 23, 2000
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