ORIGINAL RESEARCH Predictors of undergraduates’ intention to incorporate glycaemic index into dietary behaviour Robyn E. GOODWIN and Barbara A. MULLAN School of Psychology, University of Sydney, Sydney, New South Wales, Australia Abstract Aim: The present study used an extension of the theory of planned behaviour to analyse undergraduates’ intention to perform behaviour related to the glycaemic index of food. The extended model incorporated measures of past behaviour and pre-existing knowledge about glycaemic index. Methods: Seventy-two participants read an academic journal article about glycaemic index and completed ques- tionnaires measuring predictor components of the theory of planned behaviour model. Results: Subjective norm and attitude were generally observed to be the best predictors of intention. Pre-existing knowledge about glycaemic index and attitude towards restrained eating were generally found to be poor predictors of intention. Past behaviour exhibited a positive relationship with intention. Conclusions: Interventions that focus on dietary behaviour related to the glycaemic index of food should involve individuals who have relationships of influence with the target demographic, such as friends and family, and will need to address modifying ingrained patterns of behaviour. Key words: behavioural intention, diet, glycaemic index, health promotion, nutrition education, theory of planned behaviour. INTRODUCTION A recently popularised avenue of dietary research investi- gates the glycaemic index (GI) of food. GI is a property of carbohydrates that pertains to its digestive properties and effect on blood-sugar levels. 1 In the past, GI has been inves- tigated in terms of possible implications for diabetes suffer- ers. However, the extent to which everyday consumers consider the GI properties of food when forming their behavioural intentions has not been investigated. Diabetes is a lifestyle disease—the fastest growing chronic disease in Australia—and an estimated one in four adults has diabetes or an impaired glucose metabolism. 2 The majority of research and interventions focus on ‘at risk’ categories of people; however, diabetes is a symptom of pervasive lifestyle factors that result from industrialisation and modernisation of society. Replacing a high with a low-GI diet can reduce the risk of diabetes. 3 In the interests of preventive nutrition, it is imperative that the determinants of desirable dietary behav- iour be studied within the general public, and specifically among younger adults whose eating habits are a lifetime investment. In an overview of global trends in lifestyle, science and technology, Aranceta 4 investigated key themes and strategies for future community nutrition. In terms of preventive nutri- tion, GI is highlighted as central to reforming popular under- standing of what constitutes a healthy diet. In addition, dietary approaches to preventing diabetes that use the GI concept have been strongly recommended. 5 In order to com- prehensively implement GI as a key dietary consideration within society, younger people’s dietary patterns must be investigated as an imperative concern in order to effect long- term and widespread change. Several social cognition models are available for studying health behaviour. The most widely implemented of these is the theory of planned behaviour (TPB), 6,7 which is an exten- sion of the theory of reasoned action (TRA). Fishbein 8 devel- oped the TRA on the premise that attitudes serve to guide behaviour 9 and suggested that the main cause of voli- tional behaviour is an individual’s intention to perform the behaviour. Ajzen and Fishbein posit two determinants of these behavioural intentions. 10 The first is the individual’s attitude that is shaped by the collection of beliefs held by him or her, towards performing the behaviour. The second determinant of behavioural intention is that of subjective norm, which is R.E. Goodwin, BPsych(Hons), Former Student B.A. Mullan, PhD, Lecturer Correspondence: R. Goodwin, The Australian School of Business, School of Organisation and Management, University of New South Wales, Sydney, NSW 2052, Australia. Email: robyng@student.unsw.edu.au Accepted November 2008 Nutrition & Dietetics 2009; 66: 54–59 DOI: 10.1111/j.1747-0080.2008.01318.x © 2009 The Authors Journal compilation © 2009 Dietitians Association of Australia 54