Year

2012

Degree Name

Doctor of Philosophy

Department

School of Health Sciences

Abstract

One of the big challenges facing evidence-based nutrition is the apparent discord between the study of whole foods and of their constituent nutrients. Fish and long chain omega-3 polyunsaturated fatty acids (LC n-3 PUFA) are a case in point where questions lie as to the relative value of the food versus a key nutrient. Likewise, little research considers the effectiveness of dietary advice, in addition to the efficacy on health outcomes, of consuming whole foods versus nutrients, and numerous methodological challenges exist for exposing both factors. Finally, there is a paucity of biomarkers that reflect health rather than disease. An emerging biomarker of health is adiponectin, which has been associated with both fish and LC n-3 PUFA consumption; however there is little research comparing their effects on adiponectin levels. The central hypothesis of this thesis is that consuming fish may be more beneficial to health than supplements of LC n-3 PUFA, however, behavioural issues may impede the effectiveness of advice targeting habitual fish consumption.

In this thesis, methodological issues relating to fish consumption were addressed and adiponectin was considered as a biomarker of health. Data from a 12 month clinical trial involving consumption of fish and LC n-3 PUFA supplements was analysed, and a separate study comparing fish with LC n-3 PUFA supplements was conducted. It was first necessary to ensure methods were available to accurately measure fish and LC n-3 PUFA consumption. Because of the popularity of canned fish products in Australia, a database of the percentage fish in canned products was developed and validated. Dietary data collected over the duration of a 12 month clinical trial was converted to an updated Australian food composition database via a defined strategy to allow for measurement of LC n-3 PUFA intake.

Dietary methodology was applied to investigate changes in fish and LC n-3 PUFA consumption over the duration of the 12 month clinical trial and to assess compliance to intake recommendations (effectiveness of dietary advice). Fish consumption was highest at the three month time point of the trial and compliance to intake recommendations was higher for supplements than for fish. To further investigate why these patterns of consumption were seen, a study in the social research domain was conducted. Six semi-structured focus group interviews were then held to compare perceptions of fish and LC n-3 PUFA consumption in participants of the trial and control individuals from the host institution. A number of barriers to fish consumption were identified, including price, preferences of family members and availability of fish. In comparison, whilst a preference for natural alternatives to LC n-3 PUFA supplements and enriched foods was expressed, these products were perceived as a more convenient way of increasing LC n-3 PUFA consumption than fish. Participation in a clinical trial incorporating dietary advice did not appear to substantially influence perceptions of fish and LC n-3 PUFA.

The findings of this first set of studies were then used to design a six week clinical trial to compare the impact of consuming fish and LC n-3 PUFA supplements on total and high molecular weight (HMW) adiponectin levels in overweight humans. Fish consumption was found to result in a favourable increase in HMW adiponectin levels, whilst LC n-3 PUFA supplement consumption did not. This finding was made in the absence of confounding dietary or genetic factors.

This thesis provided early evidence that consuming fish may be more beneficial to health than LC n-3 PUFA supplements. It provided proof-of-concept that fish is more efficacious than LC n-3 PUFA supplement consumption in improving adiponectin levels. This research supports the value of focusing nutrition research and advice on whole foods in preference to single nutrients. However, investigation into the comparative effectiveness of advice to consume fish and LC n-3 PUFA supplements suggests that fish intake at the levels studied in this thesis may not be achievable through dietary advice alone. Future research might well identify strategies for increasing fish consumption to the level that positive effects can be achieved.

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