All About Onions
Disclaimer: This article is for educational and informational purposes only. While detailed, the article provided is not inclusive of all information on the subject. It is not intended to treat or cure any ailment, condition, or disease. The link to the full journal article and other sources are listed below.
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Facts and Supply
Onions are widely popular in cooking, from sauteing, baking, boiling, and more. The sharp, unique flavor can be mellowed, caramelized, and pickled, making it useful in dishes across many cultures. In botany, onions are in the allium genus; the species is known as the allium cepa L.¹ There are a variety of different types of onions, including red, yellow, white, sweet, and green onions.
Onions are grown primarily in China, India, and the United States (the third largest producer).¹ Within the United States, California is the top harvester of onions with over 52,000 acres in 2022.² The top importer of fresh or chilled onions is Mexico with over 925,000 pounds entering the country in 2023.² The U.S. exported the most fresh or chilled onions to Canada at over 400,000 pounds in 2023.² Currently in 2024, the August Year-to-Date (YTD) for total imports reaches over 965,000 pounds, and for total exports is over 470,000 pounds.²
Nutrient Specifics
Onions contain several vitamins and minerals; different onion species contain varying amounts of nutrients. They are all notable for containing vitamin C, choline, vitamin B5, vitamin B6, potassium, phosphorus, manganese, and calcium among other micronutrients.
Onions are rich in phytonutrients (also referred to as phytochemicals), or unique plant bioactive compounds that serve as the plants’ protection but also function in humans to promote health and wellness once consumed. Examples of phytochemicals found in onions include flavonoids, fructans, and organosulfur compounds:¹
Flavonoids: Onions contain anthocyanin and flavonols (both subclasses of flavonoids) that house the compounds quercetin, kaempferol, and isorhamnetin.¹
Organosulfur compounds: Onions contain organosulfur and sulfoxides compounds such as diallylmonosulfide (DMS), diallyldisulfide (DDS), diallyltrisulfide (DTS), diallyltetrasulfide (DTTS), PRENCSO, MCSO, and more.¹
Fructans: Carbohydrate storage in onions that are polysaccharides, such as fructooligosaccharides.¹
Other phytonutrients found within onions are saponins (which are found within the glycoside category of phytonutrients).¹
Phytonutrient Functions within the Body
The roles of these phytonutrients are pivotal in functions and reactions within the body. Through specific mechanisms, phytonutrients produce responses that can help reduce or eliminate processes, leading to a reduction or inhibition of conditions or diseases. They possess properties that are antioxidants, antibacterial, antiviral, anti-inflammatory, anticarcinogenic, antidiabetic, and more.¹ The categories below describe the functions of onion’s prominent phytochemicals.
Antioxidants
Flavonoids are known to have properties that discourage free radicals such as reactive oxygen species (ROS) from damaging cells, tissues, and organs. Quercetin is known to stop ROS and has metal-chelating properties to stop the production of free radicals.¹ Kaempferol promotes antioxidant enzymes to form and oxidizes low-density lipid protein which protects against atherosclerosis.¹
Antibacterial
Flavonoids possess antibacterial effects by reducing and impeding the functions of bacteria.¹ Quercetin is known to be effective in inhibiting S. aureus, H. pylori, and MRSA.¹ Organosulfur phytonutrients, as well as other onion and garlic properties, demonstrate antibacterial functions.
Antiviral
Flavonoids have properties that inhibit viruses by blocking the production of protein and nucleic acids the viruses rely on.¹ Quercetin and kaempferol can inhibit viruses such as rabies, polio, herpes simplex type I, parainfluenza, and more.¹
Anti Inflammatory
Flavonoids, such as quercetin and kaempferol, play a role in reducing inflammation by acting as anti-inflammatory agents. Quercetin has been found to prevent immunoglobulin formation (promoting inflammation) in vitro.¹
Anticarcinogenic
Organosulfur phytonutrients such as DPS, DPDS, SAMC, DADS, DATS, and methiin can inhibit early and late-stage cancer.¹ Flavonoids, such as quercetin, have been studied for the anticarcinogenic properties they possess through a variety of mechanisms such as inhibiting certain enzymes, halting cell proliferation, and preventing chromosomal damage.¹ Selenium phytonutrients found in onions can also provide anti-cariogenic benefits.¹
Antidiabetic
Flavonoids and organosulfur phytonutrients display antidiabetic effects. Quercetin, among other flavonoids, increases insulin; organosulfur compounds SACS and methiin stimulate insulin production and favor insulin retention.¹
Other Properties
Onions are listed to help with other conditions:
Quercetin and isorhamnetin found in onions can aid in reducing blood pressure, producing anti-hypertensive effects.¹
Organosulfur compounds found in onions produce antithrombotic effects through inhibition of thromboxane.¹
Quercetin and anthocyanin in onions can protect the liver through the prevention of iron overload in liver cells (found in mice studies) and increasing gene expression for protein kinase.¹
Saponins found in onions lower cholesterol by binding to cholesterol molecules to be excreted in feces.¹
Conclusion
Onions are beneficial for humans with the various nutrients harnessed inside. Imported by the thousands, the different types of onions can be used in several ways whether raw, cooked, or pickled. The micronutrients found within are important for wellness, and the phytochemicals play certain roles to produce effects beneficial to the body ranging from antibacterial to anticarcinogenic effects.
Pairing Education with Eating
Want to try a fun dish with onions? Click here for my Pickled Red Onion recipe!
Sources:
1. Pareek, Sunil, et al. "Onion (allium cepa L.)." Fruit and Vegetable Phytochemicals: Chemistry and Human Health, 2nd Edition (2017): 1145-1162.
2. https://www.ers.usda.gov/data-products/vegetables-and-pulses-data/
