Year

2012

Degree Name

Doctor of Philosophy

Department

School of Health Sciences

Abstract

The position of any food in the diet is the focus of much debate, yet food is central to health. As obesity and its related co-morbidities continue to compromise health status, there is a need to evaluate the position of core foods consumed by affected populations. Dairy products are a core food group which may have an important role in terms of obesity. New research suggests a significant role for gut function in the aetiology of obesity, so there may also be some value in considering the effect of dairy foods on gut health. From a negative perspective, it has been suggested that dairy products are associated with adverse metabolic health effects and can cause symptom exacerbation in gut related problems such as Crohn’s disease (CD). Both overweight and CD are increasingly prevalent and share an underlying inflammatory pathogenesis which may be related to gut health. From a dietetic practice perspective, the setting for this thesis, gaining knowledge on the position of dairy foods in these disease contexts may help to ensure that affected individuals do not unnecessarily avoid an important core food group delivering key nutrients in the diet. With this in mind, the thesis hypothesises that the position of dairy foods in the diet is complex, defined by health-disease contexts and subject to consumer behaviour.

To address the central hypothesis this research aimed to study the impact of dairy products from two health perspectives: overweight and CD. Specific objectives were to (1) evaluate associations between participants’ intake of dairy products and metabolic profiles/dietary outcomes in a 12 month weight loss trial (2) identify the association between CD patients’ intake of dairy products on CD symptoms and pathogenesis, and (3) explore the impact of dietetic education on consumer’s perceptions of dairy products. In this way some of the perceptions of diary food consumption in this context could the examined and ways to integrate dairy foods appropriately in the diet could be considered.

For analysis of dietary intake patterns, data were made available from a 12 month dietary randomized controlled weight loss trial [the ‘Smart’ study; ACTRN12608000425392]. Participants had received diet advice that included reduced fat dairy foods. Mean baseline and 3 month dairy product intake was calculated. A systematic approach to estimating dairy food intake was developed to measure dietary outcomes related to consumption of this food group. The association between milk fat consumption and adverse baseline metabolic profiles was assessed using values for validated biomarkers of milk fat intake and metabolic outcome measures. When instructed to consume reduced fat dairy products, male RCT participants reduced their overall intake of dairy products from 377.63±62.3g to 357.3±46.7g/day. In contrast females increased their consumption of carbohydrate from dairy products to the extent that a significant reduction in kilojoule intake from dairy products was no longer evident (p=0.054). Both sexes failed to meet recommended dairy product intakes (of 2-3 servings per day). Biomarkers of milk fat intake were not associated with adverse metabolic profiles and may be associated with favorable effects in the case of umbilicus circumference (r=-.291, p=.018), hip circumference (r=-.285, p=-.021) and body mass index (r=-.287, p=.018) after controlling for potential confounders. This study found that recommending reduced fat dairy products in the weight loss context may be problematic, especially for men, and indeed the need to change to these products may be questionable.

To examine the impact of dairy food consumption on Crohn’s disease, clinical data from an Auckland CD cohort were made available. Associations between self-reported effects of dairy product consumption on CD symptoms were evaluated. A nutrigenomic case-control study was also conducted to assess the influence of genetically determined lactase persistence on CD risk. Dairy product intake was found to have little influence on self-reported CD symptoms in an Auckland population. The nutrigenomic casecontrol study indicated that genetically determined lactase persistence increased the risk of CD in this population (OR=1.61, 95% CI=1.03-2.51), highlighting another potential issue for providing advice on dairy food consumption.

To examine consumer perceptions, six semi-structured focus groups were conducted with the RCT participants and compared to a control group of non-RCT University of Wollongong staff to evaluate consumer perceptions of dairy products and the impact of dietetic intervention on shaping these perceptions using the theory of planned behaviour as an interpretive framework. Non-RCT participants perceived dairy foods as weight inducing and were sceptical of functional dairy products. A lack of time/ability to decipher dairy food labels was also discussed. In contrast trial participants discussed several health benefits related to dairy foods, practised label reading and were confident to incorporate dairy foods into their diet. Nutrition education provided as a result of weight loss trial participation, influenced behavioural and control beliefs but not normative beliefs relating to dairy products. This has significant implications for practice in terms of approaches to providing guidance on dairy food consumption.

Put together these studies challenged previously held beliefs that dairy foods may be detrimental to metabolic health (in overweight people) and in CD, specifically. The results point to the need to take care when making statements for the general public and to consider particular disease and behavioural aspects when advising individuals. The importance of nutrition education to influence current beliefs/dietary outcomes in relation to this food group was illustrated, in addition to the need to consider nutrigenomic effects to gain a complete understanding of the complex and varied role of dairy foods in these disease contexts.

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