The onion is a universal herb, consumed in all regions of the world. There are several varieties, some of which are particularly rich in antioxidants. The onion is part of the large family of alliums and, like garlic, it is attributed to certain beneficial properties for health.
- Antioxidant power;
- Low in calories;
- Good source of minerals and sulfur compounds;
- Promotes cardiovascular health;
- Contributes to the prevention of certain cancers.
Nutritional and caloric values of onion
Onions are a source of manganese for women, with manganese requirements being higher for men. Manganese acts as a cofactor for several enzymes that facilitate a dozen different metabolic processes.
It also participates in the prevention of damage caused by free radicals.
In addition, onion is a source of vitamin B6. Vitamin B6, also called pyridoxine, is part of coenzymes involved in the metabolism of proteins and fatty acids as well as in the production of neurotransmitters (messengers in nerve impulses).
It also contributes to the production of red blood cells and allows them to carry more oxygen. Pyridoxine is also necessary for the transformation of glycogen into glucose and contributes to the proper functioning of the immune system.
Finally, this vitamin plays a role in the formation of certain components of nerve cells.
Finally, the onion is a source of vitamin C. The role that vitamin C plays in the body goes beyond its antioxidant properties; it also contributes to healthy bones, cartilage, teeth, and gums.
In addition, it protects against infections, promotes the absorption of the iron contained in plants, and accelerates healing.
The benefits of onion
Several prospective and epidemiological studies have shown that high consumption of vegetables and fruits reduces the risk of cardiovascular diseases, certain cancers, and other chronic diseases.
More specifically, studies indicate that the consumption of vegetables from the allium family (onion, garlic, shallot, chives, green onion, leek) could have a protective effect against stomach and intestinal cancers.
Until now, the data are insufficient to establish a link with other types of cancers (such as prostate, breast, esophagus, and lung cancers).
1. Prevention of certain cancers
Some epidemiological studies show the existence of a link between onion consumption and a reduction in the incidence of different types of cancer. First, a synthesis of case-control studies carried out in Italy and Switzerland reveals that the consumption of one to seven portions of onion per week reduces the risk of cancer in the colon, larynx, and ovaries.
Added to this is a lower risk of cancer of the esophagus, oral cavity, and pharynx with an intake of seven or more servings of onion per week.
The same trends are observed for cancers of the brain, stomach, and esophagus (studies carried out in China). Researchers from the Netherlands report an inverse relationship between onion consumption and the incidence of stomach cancer.
Finally, prostate cancer mortality would be reduced thanks to a high onion intake. The results of these observational studies must be interpreted with caution, because they do not take into account several important factors, such as the variety and cooking method of the onions, as well as the precise quantities consumed.
In addition, some studies have failed to significantly demonstrate such protective effects against cancer.
Onion could act at different stages of cancer development. Indeed, studies show that onion extracts can inhibit the mutation processes that trigger cancer. They also reduce the proliferation of cancer cells.
These results come from in vitro and animal studies. The compounds involved and the precise mechanisms of action are becoming better known and research is continuing.
2. Cardiovascular health
Onions contain compounds that act on various cardiovascular risk factors. The majority of studies on the subject have been carried out in vitro or in animals, apart from a few preliminary studies in humans.
Onion is recognized for its ability to reduce platelet aggregation in vitro, an activity that is however 13 times lower than that of garlic. Note that the aggregation of platelets in the blood increases the risk of thrombosis and, by extension, cardiovascular disease.
A recent study found that adding raw onion to the diet of pigs for six weeks did not alter platelet aggregation, but significantly lowered their blood triglyceride levels.
A preliminary study carried out on humans indicated that the consumption of approximately three medium onions (500 g), in a soup, decreased platelet aggregation ex vivo (test carried out using blood drawn from the subjects).
Also in humans, the daily consumption of approximately 220 g of cooked onion for two weeks did not make it possible to observe any positive effects on platelet aggregation.
Some studies have found that onions have less antiplatelet activity after cooking. The antiplatelet activity would be partly attributable to the sulfur compounds and the flavonoids (quercetin) of the onion. These two compounds may act synergistically. The precise modes of action have yet to be determined.
3. Strong antioxidant power
Antioxidants are compounds that protect body cells from damage caused by free radicals. The latter are very reactive molecules that would be involved in the development of cardiovascular diseases, certain cancers, and other diseases related to aging.
The main classes of onion antioxidants are anthocyanins and flavonols (more specifically quercetin). Anthocyanins give the red color to certain varieties of onion, and flavonols color yellow onions.
It should be noted that these antioxidant compounds mostly lodge in the outer layers of onions. White onions contain few antioxidants compared to yellow and red ones.
Additionally, red onion varieties generally have higher antioxidant content and antioxidant activity than light-colored onion varieties. A study conducted at Cornell University in New York State indicates that Western Yellow, New York Bold, and Northern Red onions have up to eight times the antioxidant activity of other varieties.
Along with tea and apple, onion — especially the yellow one — is a major source of quercetin. Onion quercetin would be absorbed in appreciable quantity in the body, thus resulting in an increase in antioxidant activity in the blood.
This flavonoid and other antioxidant compounds in onions could help reduce the incidence of certain cancers. Moreover, it is now well demonstrated that flavonoids, including quercetin, have a protective action against the oxidation of LDL-cholesterol (“bad” cholesterol).
Thus, a high intake of flavonols and flavones from food is associated with a lower risk of coronary heart disease.
4. Content of sulfur compounds
These substances are so named because they contain one or more sulfur atoms in their chemical structure.
Just like with garlic, sulfur compounds are formed when the onion is cut. At this time, alliin (an inactive, odorless molecule in onion) comes into contact with an enzyme and is transformed into precursor compounds for the odor, flavor, and tear properties of onion.
A series of reactions ensue the end products of which are a complex mixture of sulfur compounds contained in the onion. Some of these compounds would limit the multiplication of cancer cells, in addition to playing a role in the antiplatelet activity attributed to an onion.
These substances have the ability to reduce blood cholesterol in animals and blood coagulation in vitro, two effects sought to better prevent cardiovascular disease. However, the role of these compounds is little known in humans.
6. Excellent source of selenium
Like broccoli and garlic, onions have the ability to accumulate selenium from the soil, which leads to the formation of selenium-containing compounds.
Although it is difficult to quantify their benefits, these substances could contribute to the protective effect of onions against cancer. Research is continuing in this direction.
7. Nutritionist’s word
Do you cry when you cook the onion? Dry those tears… The molecule is responsible for the lachrymal properties of the onion (named thiopropanethial S-oxide) is released when the bulb is undone.
It is very soluble in water. This means that it can be eliminated when the peeled onion is rinsed under water or if it is cooled beforehand.
How to choose the right onion?
The onion is considered both a vegetable and a condiment. It would be native to Asia and belongs to the Amaryllidaceae family. Essential in the kitchen, it has a strong and spicy flavor that you never get tired of.
There are various varieties of onions, the most commonly consumed being the yellow onion and the red onion.
Should the onion be cooked?
Studies have shown that boiling the onion reduces its flavonoid content and thus its antioxidant activity. When the onion is cooked in a soup or a stew, this effect is of less importance, since the cooking water in which these antioxidants are found is consumed.
Conversely, baking or sautéing the onion increases its flavonoid content as the water evaporates, creating a greater concentration of these antioxidants.
The pungent flavor and strong odor of onions vary in intensity, depending on the variety. To a lesser extent, environmental factors surrounding onion cultivation (such as soil quality) also have an impact.
Eventually, the flavor and odor of onions become less strong as the weight of the onion increases. Thus, the larger onions would be less pungent and less fragrant than the smaller ones.
How to prepare onions
In the kitchen, the onion is an essential ingredient that slips easily into small daily dishes. Thanks to its pungent taste and its unique character, it brings flavor and enhances almost all preparations.
Another advantage is that it can be eaten cooked or raw in a salad, which allows you to enjoy it to the fullest.
Savor the raw onion
- Rather than sweet, Spanish, or Bermuda onions, Vidalia and Walla-Walla onions are often eaten raw, in salads, hamburgers, etc. Onions of some red varieties are also sweet, but not all of them;
- Slice a sweet onion and soak it for fifteen minutes in iced water. Drain, dry, and add salt, chopped parsley, and sumac powder (sold in Oriental grocery stores). Let stand for 15 minutes and serve;
- Soak onion slices with salt for an hour. Rinse, drain, and serve with finely chopped dill leaves;
- Serve onion rings with sliced tomatoes, feta, and black olives. Drizzle with oil and garnish with basil. Or serve them with peeled slices of orange, on lettuce, endive, or escarole leaves, all drizzled with a vinaigrette.
- Yellow onions are the most pungent of all. They are suitable for long cooking (stews, beef bourguignon) and for the preparation of stocks or stocks. In this case, we can leave them on their skin in order to give color to the broth. Onion studded with cloves is a classic in stews, broths, and more;
- Pearl onions are delicious and cooked in butter with green peas and mint. Or glazed: fry them in butter with a pinch of sugar;
- Confit onions by slicing them and browning them in a pan in melted butter. Add sugar, red wine, thyme, salt, and pepper, and simmer for about twenty minutes. Serve with grilled meat, liver, or chicken hearts;
- Stuff Spanish onions by first cutting them to three-quarters of their height and blanching them. Empty them, keeping a layer of about 1 cm. Chop the removed parts, cook them in butter, then mix them with blanched spinach, rice, or semolina. Garnish the onions and braise them in the oven for about an hour. Towards the end of cooking, add a little grated parmesan and brown. You can also stuff them with crushed garlic, oil, and parsley, or with sauerkraut and bread crumbs;
- In a pie, a soufflé, or a quiche: brown them in butter and cool them before continuing the preparation. Add bacon bits or sausage rings, if desired;
- Onion soup au gratin is prepared by sautéing thinly sliced onions in butter until nicely browned, but not burnt. We add beef or chicken broth and cook in the oven for half an hour. Put pieces of toasted bread on the broth and sprinkle with grated Parmesan cheese, then return to the oven for ten minutes. If desired, add a drop of cognac or sherry before serving. Or replace half the meat broth with cider;
- Classics of Indian cuisine, onion bhaji (khanda bhaji) is served as a starter or at tea time. Just finely chop onions and let them marinate for an hour with a little sugar and salt. When they have drained well, mix the preparation, including the liquid, with chickpea flour and chili, then form balls that are deep-fried. Serve with chutney;
- To marinate them, put the onions to soak in salted water for 12 to 24 hours. Drain, pat dry, and put in jars with mustard or dill seeds. Cover with hot vinegar, close, and keep for a few weeks before serving.
Fried onion, a good idea?
If you eat fried onion rings at a restaurant, it will be difficult to respect the dietary recommendations concerning the maximum fat per day, since these rings already contain 30 g.
As for the amount of onion hidden in it, it rarely reaches the equivalent of a portion of vegetables.
Onion contraindications and allergies
There are few contraindications to the consumption of onions nor any particularly well-known allergy. However, in people with sensitive intestines and victims of irritable bowel syndrome (IBS), the onion can cause unpleasant digestive symptoms.
In this case, consumption should be limited or adapted to personal digestive tolerance.
Irritable bowel syndrome
Irritable bowel syndrome is characterized by various disorders of the digestive system, including abdominal pain, flatulence, and changes in bowel habits. This disorder can also manifest as gastroesophageal reflux or dyspepsia.
Some people with this syndrome may experience an intolerance to various foods. Fermentable foods, such as onions, garlic, and other vegetables from the Alliaceae family are also incriminated.
The simple fact of limiting or avoiding their consumption is often enough to alleviate the symptoms. When the symptoms are mild, or during so-called “remission” periods, it is sometimes possible to gradually reintegrate these foods, always respecting individual tolerance (to find out more about this functional disorder, see the sheet Bowel syndrome irritable).
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