The Effect of a Mediterranean diet versus low-fat diet on inflammation and adiposity: an intermediate analysis of the AUSMED heart trial for secondary prevention of coronary heart disease

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the Department of Rehabilitation, Nutrition and Sport, School of Allied Health, College of Science, Health and Engineering, La Trobe University, Victoria.

Thesis with publications.

Inflammation, which is exacerbated by obesity, is a pathophysiological cause of coronary heart disease (CHD). The Mediterranean diet (MedDiet) is recognised to prevent CHD, in part, via antiinflammatory properties, however, diet efficacy via this mechanism is unclear in patients who have developed CHD. This thesis reports intermediate outcomes in pilot study participants from the AUStralian MEDiterranean Diet (AUSMED) Heart Trial, a randomised controlled trial testing the cardiovascular health benefits of MedDiet versus low-fat diet after a coronary event. The main aims were to test the effect of 6-month ad libitum MedDiet intervention on markers of inflammation, adiposity, dietary inflammatory index (DII), and MedDiet adherence in a multi-ethnic CHD cohort. Participants (62±9 years, 83 percent male, BMI 30.0±5.1kg per m2 ) were randomised to the MedDiet (n=34) or low-fat diet (n=31). Dietitian-led interviews were held at 0-, 3- and 6-months for dietary counselling, measurement of anthropometry and body composition and collection of blood samples for pathology analyses. Dietary intake was assessed via validated MedDiet adherence questionnaire and 7-day food diaries, with DII subsequently determined. Participants adhered well to the MedDiet and this led to improved diet quality and a significantly more anti-inflammatory DII score compared with low-fat diet participants after 6-months. Despite dietary changes, the MedDiet did not significantly improve inflammatory markers (C-reactive protein, interleukin-6, tumour necrosis factor-α or adiponectin), anthropometry, body composition or visceral fat compared with the low-fat diet. This lack of effect likely relates to small sample size in a medically-treated cohort. A clinically significant impact on inflammation in CHD patients may require a larger sample, adjunct exercise intervention and or caloric restriction. This is the first demonstration in Australia that dietetic promotion of MedDiet principles would lead to greater improvements in diet quality compared to current low-fat diet recommendations in cardiac patients, which in turn could more effectively impact CHD risk markers.

This thesis was a recipient of the Nancy Millis Award for theses of exceptional merit.