The love-hate relationship of onions

A look at the health benefits of onions from farm to plate

Green and leafy is what comes to mind when you think of healthy vegetables with onions being at the bottom of the favourite vegetable list. They are one of those vegetables that you either love or hate. They’re either eaten caramelised, piled on a hot dog or picked off a pizza (along with the pineapple).

Don’t be put off by their stink or ‘astringency’. Onions are a good source of vitamin C, potassium, fibre, folic acid, calcium and iron1.

Fact: onions grown in higher temperatures have a stronger smell. The flavour is also effected by the variety and the environment of the onion2.

Once picked from the farm, onions are dried in ventilated bins3, usually for two to six months with the variety influencing the drying duration4.

basket of onions

There are many types of onions, but the ones you know best will be the white onion and the red onion, often incorrectly referred to as the ‘spanish’ onion.

The darker pigments, like that of the red onion, are produced by flavonoids2. The darker the onion, the more flavonoids it contains.

You may have heard of flavonoids before. They are also found in red wine and chocolate. Flavonoids have been shown to improve blood pressure, vascular function and serum lipid levels, reducing overall risk factors for cardiovascular disease5.

When cooking with onions, take care not to peel too many outer layers off, just enough to remove the papery skin. This is because quercetin and anthocyanin (types of flavonoids) are concentrated in the outer layers. You want to keep the goodness in and over peeling reduces these flavonoids by 20% and 75% 6. Quercetin is also damaged by heat7 so keep the cooking temperature low, like in a soup where the quercetin can be imparted into the water, preserving the health benefits7.

chopped onions.jpg

The quercetin in the onion peel is highly bioavailable (easy for your body to access) and more easily absorbed due to the fibre in the vegetable’s flesh when compared to consuming onion powders and extracts8.

Do you to love whole, fresh onions now? Add some zesty onion slices to your salads and stir-fries to take advantage of their antioxidant goodness. Just brush your teeth afterwards to avoid dreaded onion-breath…

Do you love or hate onions? How do you eat them?
Share your thoughts in the comment box below.


*Any information provided by Food Hermetica is a guide only and should not replace medical advice. Reader discretion is advised.

*Food Hermetica is not affiliated with or endorse any external links found within this post. Information provided by an external link is the responsibility of the external site owner.

*Questions, compliments or complaints? Food Hermetica welcomes all constructive feedback and will endeavor to maintain a high standard of informative reporting.

  1. Onions Australia. (2015a). Benefits of onions [website]. .Retrieved from
  1. Brewster, J., L. (2008). Onions and other vegetable alliums. (2nd ed.). Wallingford, Oxfordshire: CABI.
  1. Hickey, M. (2005). AGFACTS: Onion growing. NSW Department of Primary Industries,1(22). Retrieved from assets/pdf_file/0017/126305/Onion-growing-Agfact-H8.1.22.pdf
  1. Onions Australia. (2015b). Facts & info [website]. Retrieved from /aboutonions/ facts-and-info.html
  1. Toh, J., Tan, V., Lim, P., & Chong, M. (2013). Flavonoids from fruit and vegetables: a focus on cardiovascular risk factors. Current Atherosclerosis Reports, 15(12), 1-7. doi: 10.1007/s1183-013-0368-y
  1. The George Mateljan Foundation. (2015). What’s new and beneficial about onions. Retrieved from friendly=1&tname=foodspice&dbid=45
  1. Nemeth, K., & Piskula, M., K. (2007). Food content, processing, absorption and metabolism of onion flavonoids. Critical Reviews in Food Science and Nutrition, 47(4), 397-409. doi:10.1080/10 408390600846291
  1. Kashino, Y., Murota, K., Matsuda, N., Tomotake, M., Hamano, T., Mukai, R & Terao, J. (2015). Effect of processed onions on the plasma concentration of quercetin in rats and humans. Journal of Food Science, 80(11), 2597-2602. doi: 10.1111/1750-3841.13079

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