La onion It's one of those humble vegetables that are always in the kitchen and, without making much noise, can be used in a sofrito, a comforting soup, a fresh salad, or a A sauce that makes all the differenceBehind that powerful aroma that sometimes makes us cry, lies a food packed with vitamins, minerals and plant compounds that are very interesting for health.
Beyond its reputation for making us tear up, the onion is a true nutritional and gastronomic treasureIt provides antioxidants like quercetin, prebiotic fiber to nourish the gut, sulfur compounds with antibacterial and anti-inflammatory effects, and a good number of micronutrients that support the heart, bones, and immune system. Furthermore, there are many types of onions and different ways to cook themand each of them modifies its flavor, texture and, in part, its properties.
Nutritional value and composition of onions
Onions are a food Very low in calories but nutrient-dense, ideal to include daily in a balanced diet without worrying too much about the energy it provides.
For every 100 grams of fresh onion we find approximately 38-44 kcal, 1,2 g of protein, 0,25 g of fat, 8-9 g of carbohydrates and 1,6 g of fiberThese numbers already give us a clue: it provides practically no fat, has some vegetable protein, a certain carbohydrate content and a not insignificant amount of fiber.
In terms of vitamins, onions stand out for their content of vitamin C, B vitamins (especially B6 and folate) and small amounts of vitamins A and EVitamin C contributes to the proper functioning of the immune system, to the formation of collagen and to protection against oxidative damage, while B6 and folic acid are key for energy metabolism and the nervous system.
In terms of minerals, onions provide an interesting combination of calcium, potassium, phosphorus, magnesium, manganese and traces of iron, copper, iodine, zinc and other trace elementsCalcium and phosphorus are involved in maintaining strong bones and teeth, potassium helps regulate blood pressure, and manganese and other minerals are involved in antioxidant and metabolic processes.
One of its strengths is the presence of volatile sulfur compounds and bioactive substances such as quercetin, alliin, glucoquinine, anthocyanins (in red onions), saponins and fructooligosaccharidesThese components, although they do not provide calories, are responsible for many of the benefits of onions on the heart, immune system, blood sugar, and intestines.
Special compounds in onions and why they make us cry
If there's one thing everyone associates with onions, it's that When we cut it, tears spring to our eyes.This is because, when their cells are broken, they release volatile sulfur essences which react by forming small amounts of irritating substances; one of these compounds quickly transforms into sulfuric acid upon contact with the aqueous film of the eye, causing tearing.
Among these compounds, one volatile substance stands out called Alilo, with properties bactericides and fungicidesThese types of sulfur molecules partly explain why onions are known as a traditional remedy for mild respiratory ailments and certain infections.
In addition, onions contain glucoquinine, popularly known as "plant insulin"for its ability to help lower blood sugar levelsAlthough it does not replace medical treatment in any way, its presence makes onions especially interesting in the diets of people with diabetes or insulin resistance.
Another key family are the antioxidant flavonoids such as quercetin, fisetin, lutein, and zeaxanthinPurple onions also contain anthocyanins, pigments that, in addition to providing that striking purple hue, help combat oxidative stress and may be protective against cardiovascular diseases and some types of cancer.
Finally, onions are rich in prebiotic fibers such as inulin and fructooligosaccharides, a type of carbohydrate that our body does not digest, but which feeds the beneficial bacteria in the gut, promoting a healthy microbiota.
Main health benefits of onions
The sum of its nutrients and bioactive compounds gives the onion a good repertoire of benefits backed by science and traditional experienceLet's look at them in a little more detail.
1. An ally of the heart and circulation
Thanks to its content in antioxidants, quercetin, saponins and sulfur compoundsOnions can contribute to caring for the cardiovascular system from several angles.
On the one hand, it helps to reduce LDL ("bad") cholesterol and triglyceridesThis promotes lower intestinal absorption and greater elimination through feces. This is useful for reduce the risk of atherosclerosis, heart attack and other heart problems.
On the other hand, its anti-inflammatory and vasodilatory compounds contribute to the relaxation of blood vessels and improvement of circulationQuercetin, in sufficient doses, has shown the ability to lower blood pressure in people with mild or moderate hypertension.
In addition, onions can help to prevent the formation of blood clotsThis also contributes to protecting the heart and circulatory system. All of this aligns well with recommendations to regularly include onions in the diet as part of a healthy lifestyle. cardioprotective eating pattern.
2. Antioxidant and anti-inflammatory effect
Onions contain more than 25 types of flavonoid antioxidants, especially concentrated in the outermost layers of the bulb. These compounds help to neutralize free radicals and reduce oxidative damage which, in the long term, is associated with chronic diseases such as cancer, diabetes, cardiovascular diseases and cognitive decline.
The anthocyanins from red onions have been shown, in population studies, to be related to a lower risk of heart disease and certain types of cancerThey also help protect the skin against oxidative damage that accelerates premature aging.
Quercetin and other flavonoids in onions exert a powerful anti-inflammatory effectby modulating the body's response and helping to reduce markers of systemic inflammation. This effect is relevant in chronic inflammatory diseases, metabolic disorders, and vascular health.
3. Protection against certain types of cancer
Vegetables of the genus Allium, such as onions, garlic, or leeks, have been associated with a lower risk of developing some cancersespecially of the digestive system and organs such as ovaries or lungs.
Compounds such as the following have been identified in onions: Cebionin A, which contains sulfur and which, in laboratory studies, has shown ability to slow tumor development and the spread of cancer cells ovarian and lung.
In addition to this, quercetin and fisetinflavonoids with the capacity to inhibit tumor growth, induce apoptosis (programmed cell death), and reduce oxidative stress which favors mutations.
It is worth emphasizing that onions alone are not an "anti-cancer drug," but be part of a diet rich in vegetables, fruits and minimally processed foods Yes, it is a global strategy that helps reduce the risk of these diseases.
4. Blood sugar control and diabetes support
Onions are a good ally for those who need control blood glucose, such as people with type 2 diabetes or prediabetes.
On one hand, his Fiber (including inulin) slows down the absorption of carbohydrates from the diet, smoothing out glucose spikes after meals. On the other hand, quercetin and several sulfur compounds with hypoglycemic action They influence insulin sensitivity and glucose metabolism in organs such as the liver, muscle, or adipose tissue.
Its content should also be mentioned in glucoquinine, the so-called plant insulinwhich helps to reduce blood glucose, especially when onions are consumed raw and regularly, always as part of a dietary plan prescribed by a health professional.
5. Onions and gut health
Onions provide an interesting mix of soluble fiber, insoluble fiber and prebiotic inulinThese components feed the beneficial gut microbiota, especially bacteria such as Lactobacillus and Bifidobacteriumwhich play a fundamental role in digestive and immune health.
When fermented by bacteria in the colon, the prebiotics in onions give rise to short-chain fatty acids (acetate, propionate, and butyrate)compounds that help strengthen the intestinal mucosa, reduce local inflammation and improve the integrity of the digestive barrier.
In addition, the fiber in onions It increases stool volume and stimulates transithelping to prevent constipation in the context of a diet rich in water and other vegetables. Indirectly, a healthy gut microbiota also promotes a improved absorption of minerals such as calcium and magnesium, relevant to bone health.
6. Immune system booster and antibacterial action
Combining vitamin C, antioxidants, sulfur compounds and prebiotic fiber This makes onions a good support for the immune system.
On one hand, vitamin C and flavonoids help to protect defense cells from oxidative damage and promote a more effective immune response. Furthermore, the improvement of the gut microbiota directly impacts the maturation and function of immune cellssince a large part of the immune system is located in the gut.
The sulfur compounds in onions have been shown antibacterial action against pathogens such as Escherichia coli, Staphylococcus aureus or Bacillus cereusAmong others. Quercetin extracted from onion skin can even damage the cell membrane of certain bacteria and hinder their proliferation.
That is why, traditionally, onions have been used in Home remedies for flu, colds, and bronchitis, both in the form of syrups and infusions or simply by placing half an onion next to the bed to relieve nighttime congestion (although this last practice has more popular support than scientific evidence).
7. Bone health and osteoporosis prevention
Although we usually associate bone health with milk and dairy products, onions also contribute their bit thanks to their antioxidants, sulfur compounds, and the ability to modulate inflammation.
Studies in middle-aged and postmenopausal women have observed that a Regular consumption of onions is associated with higher bone mineral density and with a lower risk of hip fracture compared to those who barely consume it.
Onions are believed to contribute to reduce oxidative stress and bone lossand that, combined with a diet rich in calcium, vitamin D and physical activity, can help prevent osteoporosis or slow its progression.
8. Helps with flu, colds, and respiratory issues
From folk wisdom to some modern studies, the onion has been used as natural remedy to relieve cough, mucus and cold symptoms.
Taken in the form of teas, homemade syrups, or even as an infusion of the peelsOnions have a mild expectorant effect, helping to thin secretions and aiding in their expulsion, which can relieve mild bronchitis, colds, or flu.
Its antiseptic and anti-inflammatory action, linked to sulfur compounds and quercetin, supports this traditional use of “ally against colds”always as a complement and not as a substitute for medical treatment when necessary.
Different types of onions and their uses in cooking
In the market we don't just find a generic onion; there are multiple varieties with different flavors, colors and textures that fit better in some recipes or others.
The white onion, the most common type, is very versatile for stir-fries, stews, omelets, sauces and soupsWhen cooked slowly, its natural sugars caramelize and it becomes a sweet and aromatic base for countless dishes.
La purple OnionWith its intense color and slightly spicier flavor, it's ideal for salads, pickled dishes, guacamole and fresh sauceswhere it adds both flavor and a vibrant touch of color. Furthermore, it is rich in anthocyanins, which adds to its antioxidant properties.
La Figueres onionTypical of Catalonia, it is characterized by its crispy texture and mild, slightly sweet flavor. It is perfect for Consume raw in salads, with tomato, with cheese or sausagesor even in sandwiches and toast.
The spring onions or green onions They are widely used in Asian, Mexican, and Mediterranean cuisine. Their green stem and small bulb are highly valued for decorate dishes, finish stir-fries, prepare quick stir-fries, or add a fresh touch to soups and Rice dishes.
Los calçots, a variety closely linked to Catalan tradition, resemble a thick spring onion and are eaten grilled over charcoal and served with romesco sauce in the famous calçotades, a proper gastronomic festival.
The sweet onions (like Vidalia or similar varieties) have a particularly mild, almost honeyed flavor, and are used in salads, savory tarts, candied fruits and recipes that seek natural sweetness without the itching dominating.
Finally, the shallots or scallions These are small, thin onions with a more delicate texture and a mild, fragrant flavor. They are ideal for fine sauces, vinaigrettes, reductions and French or haute cuisine dishes where a touch of onion is desired without it being aggressive.
Ways to consume onions and how they influence their properties
The way we cook onions not only changes their flavor and texture, it can also partially modify its nutritional propertiesThe interesting thing is to combine different techniques throughout the week.
Raw onion
Eat the onion raw, either in salads, vegetable carpaccios, fresh sauces or as a side dishIt allows for the maximum use of heat-sensitive compounds, such as some antioxidants and glucoquinine.
Quercetin and certain sulfur compounds are found especially concentrated and stable in raw onionsThis translates into greater antioxidant and anti-inflammatory potential. It's the best way to fully enjoy its benefits. protective capacity against free radicals and its vasodilatory effect.
Cooked onion
When we cook onions, especially over low heat and for a reasonable amount of time, transformations occur that can improve the bioavailability of some compounds and make it more digestible for those who do not tolerate raw onions well.
Cooking alters sulfur compounds, but it can also facilitate the absorption of certain antioxidantsIn addition, the texture becomes softer and sweeter, which makes it more pleasant to the palate and easier to digest for sensitive stomachs.
Fried onion
Frying onions, whether for a sofrito, to serve them crispy, or as the base of a sauce, involves adding oil and intense heat, which significantly changes both the nutritional and organoleptic profile.
On the one hand, it increases the calorie content of the dish by adding fat; on the other hand, frying makes the The onion's natural sugars partially caramelizeintensifying its flavor and providing that slightly crispy and golden texture that is so appealing.
To minimize nutritional losses and avoid bad quality fats, it is advisable Use oils with a high smoke point (such as extra virgin olive oil over moderate heat) and remove excess fat with absorbent paper if you are looking for a lighter preparation.
Caramelized onion
Caramelized onions are obtained by cooking them very slowly over low heat until the sugars concentrate and they turn a deep golden color. It can be made with just the onion or with a small amount of sugar.
This process concentrates flavors and creates a sweet, honeyed and very aromatic onionPerfect for accompanying meats, cheeses, hamburgers, savory tarts, or toast. Despite losing some heat-sensitive vitamins, it still retains... antioxidants and some of their sulfur compoundsas well as gaining in gastronomic complexity.
Tips for getting the most out of onions
If we want to get the most out of this vegetable, it's worth keeping a few things in mind. tips for buying, storing and cooking that help preserve their nutrients.
Choosing and properly storing onions
When buying, it's important to choose firm bulbs, heavy for their size, without sprouts, bruises or soft spots and with the skin dry and well-adhered. These details are a sign of freshness and good preservation.
Once home, it's best to store them in a cool, dry, ventilated and dark placeAvoid humidity and direct sunlight. Do not stack them too high to allow for air circulation and prevent mold growth.
Organic vs. conventional onions
Whenever budget and availability allow, one can opt for organically grown onionswhich they usually present lower presence of pesticide residues and, in some cases, slight differences in certain phytochemical compounds.
In any case, whether they are organic or not, it is advisable Wash the onion well before peeling itto prevent any possible traces of soil or substances from the shell from passing inside with the knife or hands.
Cooking techniques to preserve nutrients
If we want to preserve as many heat-sensitive antioxidants as possible, such as vitamin C or some quercetin, it's best to opt for gentle and not excessively long cooking times, such as steaming, short stir-fries, or low-temperature baking.
It also helps to combine raw and cooked onion Throughout the day: in salads, as a topping for hot dishes or in fresh side dishes, and in soups, stews or stir-fries to take advantage of their flavor and texture.
Recipe ideas featuring onions as the main ingredient
Theory is all well and good, but where onions truly shine is in practice. Here are some examples. classic recipes and some slightly more original ones in which this vegetable shines with its own light.
French-style onion soup
French onion soup is a spoon dish comforting, full of flavor and very easy to prepare, perfect for cold days.
It is made by slowly caramelizing. sliced onions with butter or oil until they are nicely browned, then add garlic, a little flour to thicken it, meat or vegetable stock and, if desired, white wineAfter a gentle boil, it is served au gratin in the oven with slices of toasted bread and melted cheese on top.
Savory onion and cheese tart
Another great way to make onions the star of the show is to prepare a savory onion tart with a shortcrust pastry baseThe result is perfect for a casual dinner or to take to a meal with friends.
Caramelize the onions in a pan with olive oil until very tender and golden brown, let them cool slightly and mix with beaten eggs, liquid cream or evaporated milk and a good amount of grated cheese (Gruyere, Cheddar, or a mixture). Everything is poured over the dough spread in a mold and baked until set and golden brown.
Onion chutney
Onion chutney is a sweet and sour preserve ideal for to accompany meats, cheeses, hamburgers or sandwichesand adds a different touch to any cheese board.
To prepare it, they are cooked slowly. Sliced red onions with apple, brown sugar, vinegar, ginger, mustard and cumin seeds, cinnamon, salt and pepperAfter prolonged cooking over low heat, the mixture thickens and is stored in jars, where it can be store for several weeks in the fridge.
Onion peel tea
A simple and traditional recipe is the tea made with onion peels, which are used instead of being thrown away.
Simply wash the skins of two onions thoroughly, boil a liter of water, remove from the heat, add the peels, and let it steep for a few minutes. Strain and drink while still warm. This tea has been traditionally used as support to relieve coughs and minor respiratory discomfort.
Preserved or pickled onions
Pickled onions are a delicious way to add Add acidic and crunchy touches to tacos, salads, sandwiches, or meat dishes.
It is prepared by mixing vinegar (for example, apple cider vinegar), salt, sugar, and thin slices of red onion in a jar. After resting for a while in the refrigerator, the onion becomes an even more vibrant color and acquires a highly addictive acidic and slightly sweet flavor.
Red onion and lemon salad
For lovers of fresh and bold flavors, a salad of red onion with lemon wedges, garlic, sugar, olive oil, salt, pepper and parsley It's an ideal side dish for grilled fish, meats or baked dishes.
The citrusy note of the lemon and the light sweetness balance the spicy touch of the onion, giving a a very aromatic and digestive blend.
Onion: fruit or vegetable?
Although it may seem like an anecdotal question, it is worth clarifying that the onion is the bulb of the Allium cepa plant and is clearly classified as vegetable.
From a botanical point of view, fruits are the parts of the plant that contain the seeds and help in its dispersal, something that does not happen in the case of the onion, whose edible part is precisely that underground bulb where it accumulates reserves.
Contraindications and people who should take precautions
Despite its many benefits, onions don't agree with everyone equally, and there are cases in which it is advisable to moderate its consumption or avoid it.
People with onion allergy or intolerance They should eliminate it from their diet and always consult a health professional if they suspect adverse reactions after consuming it.
Those who suffer irritable bowel syndrome, gastritis, gastroesophageal reflux, or tend to have a lot of gas People may experience digestive discomfort, bloating, heartburn, or abdominal pain when eating onions, especially raw ones. In these cases, it's best to cook them thoroughly, reduce the amount, or, if necessary, avoid them altogether.
Beyond these specific situations, for the rest of the healthy population, onions can be a regular part of the diet, always within the framework of a a varied diet and a healthy lifestyle.
With all its nutritional benefits, its positive effects on the heart, gut, immunity and bones, and the amount of recipes and cooking techniques in which she can shineThe onion is confirmed as a pantry staple vegetable that deserves to be on the table every day, whether raw, caramelized, in soup, pickled, or as the base of almost any savory dish that comes to mind.
