They may make us cry but onions are actually good for us, and researchers in China are beginning to explain why…
Levels of plasma total cholesterol (TC) correlate directly with the risk of coronary heart disease, one of the biggest killers worldwide. Previous studies have shown that onion favourably modifies TC levels, but the underlying mechanism is not understood.
Hau Yin Chung, Zhen Yu Chen and co-workers studied the effect of dietary onion powder with the protein expression of key receptors and enzymes involved in cholesterol metabolism. Results demonstrated that onion decreased plasma TC in a dose-dependent manner, accompanied by enhanced excretion of fecal sterols.
Expression analysis demonstrated an upregulation in the expression of liver X receptor-alpha (LXRα), a protein which activates the production of cholesterol-7α-hydroxylase (CYP7A1). CYP7A1 is a rate-limiting enzyme in the conversion of cholesterol to bile acids and is responsible for the elimination of excessive cholesterol in the liver. This study shows that it is the upregulation of CYP7A1 which is most likely to explain the decreased plasma TC and enhanced fecal sterol excretion.
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