Onions are a popular vegetable under the plant genus allium and are related to many other plants including garlic, leek, and shallots. It is shown that this vegetable has been used for thousands of years as an essential nutritional food source in many cultures.
The origin of this plant is believed by many to be from central Asia, where its popularity allowed it to spread throughout the world. There is another belief that the plant could have originated from the middle east. Although its exact origin is unknown, what is known is its popularity and how extensively it was used throughout the years as a main component for people’s dietary lifestyle. There is some evidence showing that onions were cultivated for consumption at least 5000 years ago in China and Egypt, though they are believed to have been grown for even longer.
In Europe during the middle ages, onions played a significant part of the people’s diet. Onions were valued as they added flavour and nutrition to meals and were easy to store, fast growing, and used to treat conditions such as colds and headaches. Not only were onions a important staple in European diet, they were also used as a method of payment instead of money and were even given as gifts during weddings. When American settlers arrived the first plant that they brought with them and grew was the onion due to its nutritional value. During this time it was also discovered that American natives ate a type of wild onion as part of their diet. The importance of onions is not just limited to its use as a meal source. Various cultures believed that this vegetable contained special properties. The Egyptians viewed onions as a symbol of eternity. They displayed onions in paintings and used them in the burial process of the pharaohs.
Onions range from having a milder, sweet taste to the strong, pungent flavour they are commonly known for, depending on the variety as well as the growing conditions and time of harvest. Yellow onions have the richest flavour making them the most versatile. They are also the most common onion produced with about 87% of onions grown in the United States being the yellow onion variety. The second most popular onion produced in the US is the red onion which accounts for 8% of onion production, with the remaining onion production being the white onion.
One of the biggest factors that determines the flavour and intensity of the onion is the season it is grown and picked. Spring/summer onions are grown from March to August, depending on where they are grown. The characteristics of spring/summer onions generally consists of a sweeter to milder flavour, thinner and lighter coloured skin, smaller size, and greater water content. These onions have a shorter shelf life due to their water content and are more susceptible to bruising. The specialty sweet onions that are available are under the spring/summer growing season. Fall/winter onions are available from August to May with characteristics that generally include thicker and darker coloured skin, less water content, larger size, and with flavours that range from mild to pungent. Due to their lower water content, fall/winter onions have a longer shelf life.
Red onions have a milder onion flavour at first harvest but gain a slightly pungent taste during second harvest and can become sharp and spicy, with a moderate to very pungent flavour. White onions have two harvest time periods, with the first harvest having a moderately pungent flavour with little very aftertaste. The second harvest may either be moderately pungent or may develop a very strong pungent taste. They have very little aftertaste when compared to both red and yellow varieties during their last harvest.
Yellow onions also range in flavour depending on their harvest time. During first harvest, they tend to be crisp and juicy with a mild flavour that has a slightly sweet ending with little to no aftertaste. The second harvest is still considered to be crisp and juicy but they develop a mild to slightly pungent flavour with a faint aftertaste. It is the last harvest that contains a strong pungent flavour with a mild aftertaste due to the high sulphur content. In addition, there are special onion varieties under the three main onion types that are produced for being sweeter or having an even stronger onion flavour.
Onions are a good source of many nutrients. They are a good source of vitamins, with 160 grams of onions having 0.1 mg of vitamin B1 (thiamin), 0.2 mg vitamin B6, 6 mcg biotin, 30 mcg folate, and 11.8 mg vitamin C. In mineral content, they are a good source of copper with 0.1 mg, manganese with 0.21 mg, phosphorus with 46 mg, and potassium with 234 mg. Onions also contain 2.7 grams of fibre and are a good source of protein, with 1.8 grams.
Some of its greatest and more well-known benefits come from its flavonoids and sulphur compounds. Onions are very high in flavonoids, in particular the flavonoid quercetin. Quercetin is a flavonoid that is responsible for giving plants their colour and provides many health benefits. It is able to help reduce cholesterol, fight and prevent cancer, reduce blood pressure, help with arthritis, and reduce chances of atherosclerosis. Consuming quercetin in onions is able to provide better function and protection from oxidative stress than even a purified supplemental form.
Each of the onion varieties contain different nutritional properties, with their flavonoid content being the biggest separation. Red onions have the highest amount of flavonoid, followed by yellow onions and then white onions. White onions contain a much lower amount of flavonoid than yellow onions. Red onions contain two unique components that are not present in other varieties; the flavonoid anthocyanin and the carotenoid lycopene, which give red onions their colour.
Onions contain the flavonoid quercetin which acts as both an anti-inflammatory and as an antioxidant. This flavonoid has shown the ability to relax airways muscles helping in relieving asthma symptoms. Its antioxidant properties not only strengthens the immune system by removing free radicals but also by reducing allergic reaction by stopping the body from producing histamines. Histamines are part of the immune system that plays a role in making people sneeze, cry, and itch when having an allergic reaction.
Quercetin helps our arteries by allowing our blood to flow efficiently by preventing blockages due to plaque buildup, which reduces risk of heart attack and stroke. The absorption of this flavonoid is twice as high in onions than in tea and three times more than in apples. Both tea and apples are known for their high quercetin content. Out of the onion varieties, red contains the highest amount of quercetin and white onions the least amount of quercetin and other antioxidants.
Onions are high in sulphur content, which play a role in their unique taste and odour. Cutting onions causes its sulphur acids and enzymes to react which results in the production of the sulphur compound propanethiol S-oxide. It is due to the propanethiol S-oxide reacting to the water in our eyes that causes us to tear up when cutting the onions. Not all onions will cause the eyes to water, as certain onions contain less sulphur. Yellow has the greatest sulphur content while white tends to contain much less. The sulphur content is an important part of the health properties that onions provide. The sulphur contains anti inflammatory properties due to their ability in inhibiting the body’s macrophage cells.
Onions have shown to contain powerful anticancer properties, with increased intake resulting in higher benefits. A moderate intake, 1-2 onions per week, had the results of preventing colorectal, laryngeal, renal cell, and ovarian cancer. High onion consumption, almost daily, was further shown to help prevent cancer that occurs in the mouth, kidney, esophagus, and breasts. Even higher amounts, daily consumption, of the vegetable is shown to have even more potent ability in preventing almost all types of cancer.
The more potent onions have been shown to be able to reduce unwanted platelet activity. High platelet activity causes unwanted blood clotting, increasing the chance of heart attack, atherosclerosis, and stroke. In addition, they provide more benefits for a healthy heart as they are have shown to act as a natural blood thinner due to the sulphur. The components in onions cause an increase in the amount of the messaging molecule oxylipin, which helps in regulating the body’s blood fat level and its level of cholesterol.
Onions provide good benefits to our digestion system with its fibre content, which helps prevent the spiking of glucose levels and allows unwanted waste to be removed from the system. They are also unique in their fibre content as onions contain a special fibre called oligofructose. Oligofructose helps promote the good bacteria in our system and have shown to help prevent and treat types of diarrhea.
Another health benefit of onions is their effect on lowering glucose levels. Onions have been shown to reduce fasting blood glucose levels and help against hyperglycemia (high blood sugar levels) when taken in a dose dependent manner. This means there is a direct connection between the amount of onions eaten and their effect. In this case, the more onions that are consumed, the greater the benefit in being able to reduce fasting glucose levels and helping prevent against hyperglycemia. A couple of ways onions have this ability is due to the presence of chromium and sulphur. The chromium is able to assists the body’s ability to regulate glucose levels while sulphur is able to trigger increased insulin production. Onion’s ability to lower glucose levels is beneficial in helping to control and prevent high blood glucose levels in conditions such as diabetes or those with uncontrolled glucose levels.
There are some things a person need to be mindful of when consuming onions. One of them is that a high concentration of their flavonoids are present in the outer layers of skin. A person needs to be careful that they only take off the outer layer they need to, or they miss out on a large portion of the flavonoid content. Eating large amounts or rapidly increasing the amount of green onions can interfere with blood thinning drugs due to their high vitamin K amount. Vitamin K is an essential vitamin that plays an important role in bone health and blood clotting. It’s role in blood clotting prevents us from bleeding but it is also what may cause it to interfere with blood thinners, particularly when consumed in large amounts.
Onions should be as fresh as possible to get their maximum benefits. Proper storage is needed for onions as even though they can keep for a long time, spoilable is possible. This is especially true for chopped onions which spoil much faster. Slowing down the spoilage is simply storing them in the fridge, with chopped onions being placed in a closed container when in the fridge.
It is due to the many health benefits of onions that they have been used throughout the years as a source of medicine. They have been used to treat or help protect against conditions such as colds, high blood pressure, heart attacks, stroke, joint problems, and illnesses, along with many other health complications. Even now many people include onion as part of their meals to ward off or prevent many health problems.
Onions are an amazing vegetable that provides plenty of health benefits with their unique sulphur content, powerful flavonoids, and good vitamin and mineral content, along with other beneficial properties. A moderate consumption will give a good amount of these benefits with greater consumption even more potent properties. With their unique flavour, onions are an easy to use vegetable that can be used in a wide variety of recipes to get beneficial properties for a healthy lifestyle.
