Fruit and vegetables : factors affecting their consumption
The purpose of this thesis was to study food choice motivations in relation to fruit and vegetable consumption. To this end, four studies were undertaken. The first was a systematic review of the literature investigating factors affecting the food choice decisions of adults in relation to fruit and vegetable consumption. The second study examined the different health and lifestyle factors, which affect fruit and vegetable consumption in women. Participants were drawn from the UK Women's Cohort Study (UKWCS), and were all females, aged 35-69 years (n = 35,367). These women provided health and lifestyle information including a 217-item food frequency questionnaire. The strongest predictors of a high level of fruit and vegetable consumption found in the logistic regression model were: being a vegetarian or vegan, taking vitamin or mineral supplements, being married, having an A-level or degree level of education and belonging to a higher socio-economic group. The third study explored the priorities of high consumers of fruit and vegetables compared to lower consumers, within 998 women from the UKWCS, using the Food Choice Questionnaire. In a multiple linear regression model the strongest motivations affecting specifically fruit and vegetable intake were health and natural content. This study also investigated the relationships between food choice motivations and the process of behaviour change, using the Stages of Change (SOC) ModeL The SOC evaluation showed significant associations with portions of fruit and vegetables consumed, and the findings showed that women classified in differing phases of SOC model have different food choice motivations. The final study assessed the variability and validity of plasma nutrient levels as biomarkers of fruit and vegetable intake. Participants were 54 non-smoking women recruited from the UKWCS. Two methods, the food frequency questionnaire and the 4-day food diary were employed to assess fruit and vegetable intakes. The results implied that the practice of using plasma biomarkers simply as a proxy measure of dietary intake is not valid and emphasise that plasma biomarkers are not simply a reflection of dietary intake but also of a number of physiological processes. Overall, the findings demonstrated: that health promotion interventions to increase fruit and vegetable consumption should primarily be targeted at people who smoke, live alone and are of a lower education level and socio-economic status; that higher consumers of fruit and vegetables tend to be more motivated by health concerns and the natural content of the food, and less motivated by convenience and familiarity issues, than the lower consumers of fruit and vegetables; that people classified in different Stages of Change have differing food choice motivations and finally; that plasma antioxidant levels are not biochemical markers of accurate dietary intakes, at either the food or nutrient level, however they may give a more complete assessment of diet when used in conjunction with traditional dietary assessment methods.