Year

2012

Degree Name

Doctor of Philosophy

Department

School of Health Sciences

Abstract

Functional foods may have a role to play in either preventing or treating obesity. Both preventive and treatment studies were carried out in this project. The preventive study was carried out in rats fed a high-fat diet (HFD) adding low dose (LD), medium dose (MD) and high dose (HD) of Oats (O) and Shiitake mushroom (M) containing 2g/kg, 6g/kg and 18g/kg beta-glucans (LD-O, MD-O, HD-O and LD-M, MD-M, HD-M) compared to HFD control group for 6 weeks. The treatment study was carried out in obese rats induced by HFD for 8 weeks followed by adding Shiitake mushroom powder containing 6g/kg, 12g/kg and 18g/kg beta-glucans in the diets as low, medium and high doses.

The interesting findings of this study overall are, the diets with a Shiitake mushroom appeared to be stronger lowering plasma lipid than the diets with enriched oats which include their beneficial effect in lowering weight.

The results showed that both oats and Shiitake mushroom enriched diets had significantly higher faecal fat exclusion compared to the HFD; while Shiitake mushroom enriched diet had lower levels of plasma triacylglycerol (TAG) level, total fat mass deposition and body weight gain compared to oat enriched diets. The HD-M group had the highest amount of faecal fat exclusion among all groups. In comparison to HFD, the HD-M diet prevented the increase in plasma TAG, fat deposition and body fat index and also resulted in decreased energy efficiency. Negative correlations were found between the amount of Shiitake mushroom supplementation and body weight gain, plasma TAG, and total fat masses.

This study demonstrated that lowering of plasma TAG and prevention of BWG using a Shiitake mushroom enriched diet was also possibly influenced by eritadenine content in Shiitake mushroom. We found that the HD-M group significantly increased liver weight per 100 g body weight and liver TAG compared with rats fed the LD-M and MD-M diets but it was not significantly different from rats fed the HFD. The rats in the HD-M group showed the highest incidence of hepatic ballooning, resulting from decreased ratio of liver phosphatidylcholine (PC) to phosphatidylethanolamine (PE), which can probably be attributed to eritadenine contained in Shiitake mushrooms. This decrease ratio of PC to PE has been associated with increase membrane permeability and hence promoting influx of lipoproteins into the liver.

Unlike the prevention study, the treatment study showed no significant effects. The Shiitake mushroom did not accomplish the dietary treatment effect on existing obesity.

In conclusion, this study revealed that a Shiitake mushroom enriched diet was more powerful in preventing high-fat diet induced obesity than oats enriched diet through the increased fat faecal exclusion; however, increased TAG in liver can be an issue when ingesting a high dose of Shiitake mushroom. But, the addition of choline chloride to the diet may help to prevent this side effect. This warrants further investigation. The treatment study showed that shiitake mushroom enriched diet was not sufficient to reverse obesity. This information may provide significant information assisting the use of Shiitake mushrooms and oats as functional foods for the prevention of obesity.

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.