Scientists unearth secret health properties of onions

They may make people cry, but scientists have finally discovered why red onions are good for the heart after unearthing their health properties.

Researchers proved for the first time how the vegetable's effects can reduce heart disease by retaining "good cholesterol" and removing "bad cholesterol" from the body.

Chinese researchers bought a basketful of red onions from their local market and began studying the onions' health properties after feeding them to hamsters. The 36 male hamsters were randomly divided into three groups and fed a high-cholesterol control diet or the two experimental diets supplemented with either 1 per cent onion powder (OP-1) or 5 per cent onion powder (OP-5) for a period of 8 weeks. The powder was derived from boiling the onions before filtering and spray-drying the extract.

The team found the groups who were fed the onion-powdered diet saw their levels of "bad cholesterol" (low-density lipoprotein or LDL) drop, while simultaneously managing to retain high levels of "good cholesterol" (high-density lipoprotein or HDL). At weeks 4 and 8, cholesterol levels of the OP-5 group decreased by 11.2 per cent and 20.3 per cent compared with the control group. Although cholesterol levels were lower in the OP-1 group, they were not statistically different from the control hamsters.

The scientists' work features in the first issue of the new Royal Society of Chemistry journal, Food and Function. 

Red onions are a popular ingredient to salads, marinades, salsas and roasts and the sweet flavour of Italian red onions means they are often used to make marmalades, thanks to their extra juiciness. Although it has been shown that the onion possesses various biological activities, such as being an antibiotic and antidiabetic, the chemistry of onions has been the subject of many investigations. 

Lead researcher Zhen Yu Chen, from the Chinese University of Hong Kong, said: "Despite extensive research on onions, little is known of how their consumption interacts with human genes and proteins involved in cholesterol metabolism within the body. Our study was therefore undertaken to characterise the interaction of onions with enzymes in an attempt to explore the underlying cholesterol-lowering mechanism.

"This study was the first of its kind to investigate the interaction of red onions with biological functions. Results demonstrated that the onions decreased cholesterol levels in a does-dependant manner. The results support the claim that the regular consumption of onions reduces the risk of coronary heart disease."

Notes for editors:

• HDL and LDL are two of the five major groups of lipoproteins which, in order of size, are chylomicrons, VLDL, IDL, LDL and HDL. In healthy individuals, about 30 per cent of blood cholesterol is carried by HDL.

References

Hypocholesterolemic activity of onion is mediated by enhancing excretion of fecal sterols in hamsters 
Lei Guan, Hau Yin Chung, Yalun Su, Rui Jiao, Cheng Peng and Zhen Yu Chen
Food & Function, 2010, Advance Article
DOI: 10.1039/C0FO00036A