Abstract
Dietitians assess intake and motivational readiness to change (Stages of Change) so as to provide counseling. However, studies of stage distribution in the population rely on survey instruments based on self-assessed intake rather than on dietitian-assessed intake. The purpose of this study is to describe a stages of change classification system based on an interview and to describe stage distribution in young adults. In addition, we compared servings defined by dietary interview for fruits, vegetables, or grains to a person's self-assessed intake. Two hundred thirteen young adults (age 18-24 years) were recruited by telephone from random lists in 8 states stratified by gender and college status. Subjects described self-assessed number of servings for one food group and then completed a dietary interview for the food group, defining servings using Food Guide Pyramid portions. Stages of change was assessed in the interview using Food Guide Pyramid recommendations as criteria for action. Servings were normalized by square root transformation prior to analysis of variance and t tests. Sensitivity and specificity compared self-assessed servings to servings determined by dietary interview. Differences between self-assessed number of servings and dietary interview defined servings were calculated to quantify error in self-assessment. We found median intake was 2.5 servings fruit, 3.5 servings vegetables, and 5.5 servings grains. Self-assessed servings differed by stages of change overall (F = 8.7 fruit, 7.2 grains, P <= .001; F = 2.6 vegetables, P <= .05) and comparing preaction to postaction stages (t = 4 fruits, 4.9 grains, P <= .001; t = 2.3 vegetables, P <= .01). Sixty-three to sixty-eight percent of subjects were in action or maintenance for fruits and vegetables and 50% for grains. Sensitivity and specificity were high for fruit (84, 80), moderate for vegetables (68, 67), and inconsistent for grains (32, 90). Most subjects (70%) assessed their fruit intake within 1 serving compared to interview assessment, but mean error was 1.6 servings vegetables, and 2.8 servings grains. Stages of change classification based on a dietary interview may be useful for assessing motivational readiness to meet specific dietary targets. The interview is particularly important for grains because of the pervasive difficulties in self-assessment of intake for this food group in young adults. Self-assessment of intake appears relatively accurate for fruit and marginal for vegetables.
CONSUMPTION OF fruits, vegetables, and grains strongly relates to a decreased risk of developing chronic diseases. 1,2 The 2000 edition of the Dietary Guidelines for Americans places great importance on increasing consumption of foods from plant origins. 3 However, the typical American diet includes too few grain products, vegetables, and fruits. 4-9 Young adults between the ages of 18 and 24 are at a critical stage of development because they are making the transition from parental control of food intake to being responsible for their own food intake. 10-12 Food habits adopted during the young adult years have long-term effects on health throughout life and are the habits that will be taught to the next generation of children. However, young adults, like older adults, consume too few foods of plant origin. 7,13-17
Newer models for promoting behavior change such as the Stages of Change Model 18 show promise. Although the model has been used in interventions for increasing the consumption of fruits and vegetables in adults, 19-21 studies have only recently applied this model to young adults. 22 One problem in applying the model to dietary habits of young adults is their lack of awareness of their intake. Stages of change classification requires a clear definition of the target behavior, self-assessment of whether or not one has met the target, and either assessment of how long the target has been met or motivational readiness to change to meet the target. 23 If people are optimistically biased in self-assessment, this could lead to classification in the action or maintenance stage even though the person fails to meet the target behavior. 24-27
Compounding errors in self-assessment are errors associated with different methods of dietary assessment. For example, food frequency instruments tend to underestimate or overestimate servings of fruits and vegetables in proportion to the number of questions used to assess intake. 28 In addition, subjects often err in portion size estimation and misclassify foods, such as fruit drinks for fruit juices. 29,30 Although dietary recalls assess a previous day's intake fairly accurately, 31 and portion sizes as well as food items such as fruit drinks can be clarified in probes, a single interview is unreliable due to day-to-day variability. 32,33 One solution commonly used in clinical settings is the dietary interview where a recall is used as a starting point in determining usual eating patterns. 34 Dietary interviews provide an opportunity to define a target behavior for stage classification independent from self-assessment bias. The dietary interview method has been used in assessing stages of change for dairy product consumption in adult women, 35 and a food frequency questionnaire combined with an interview was used for assessing fruit, vegetable, and grain consumption in adults in Singapore. 25 However, interviewer-assisted staging has not been used for young adults. In addition, this study is the only one in which fruit and vegetable intakes were assessed separately for young adults. Most researchers, including Ling and Horwath, 25 combine fruits and vegetables, which could cause problems with stage classification if these food groups are perceived differently. 36 This study used a clinical approach along with a dietary interview to determine fruit, vegetable, or grain consumption, which formed the basis for assessment of stage of motivational readiness to consume recommended amounts of the target food group. Although appropriate in clinical settings, the dietary interview method is not relevant for community interventions where individual interviews are prohibitive and self-assessment is the only option for stage classification. 23 The purpose of the study was to (1) describe stages of change for fruits, vegetables, and grains in young adults based on interviewer-assisted staging and (2) validate use of self-assessed intake for stages of change classification by comparing self-assessed intake to a dietary interview that assessed number of servings of these foods.