As a member of the Allium family of vegetables, onions share some nutritional benefits with garlic and leeks, which are also members of this Allium family. Other allium vegetables include chives, shallots, and scallions. At WHFoods, our minimum recommended daily intake level for allium vegetables is one-third serving per day. Our outstanding recommended intake is two-thirds serving per day. For onions, one-third of a serving would be one-third cup chopped and cooked. For leeks, this same serving size would apply. For garlic, one-third of a serving would be 2 cloves. To achieve outstanding daily intake, you would simply double these amounts. Our World's Healthiest Foods Meal Plan is a great place to start if you want to see how easy it is to bring onions into your weekly meals in an amazingly delicious way. Our World's Healthiest Foods Meal Plan averages one half cup of onions per day - an amount which exceeds our minimum recommended amount for all allium vegetables combined! And you will find onions being included on every single day of our World's Healthiest Foods Meal Plan.
While onions rank in our WHFoods rating system as a very good source of biotin and a good source of manganese, vitamin B6, copper, vitamin C, fiber, phosphorus, potassium, folate, and vitamin B1, this richness in conventional nutrients is accompanied by their unique phytonutrient content. While a good number of the unique phytonutrients found in onions are sulfur-containing, many are not. The chart below shows onion phytonutrients that are receiving special attention in today's health research:
|Flavonoids||Organic Acids||Sulfur-Containing Compounds|
|fisetin||ferulic acid||dimethyltrisulfide (DMTS)|
|quercetin||protocatechuic acid||S-1-propenyl-1-cysteine sulfoxide (PRENCSO)|
|kaempferol||myristic acid||DMS (diallyl monosulfide)|
|isorhamnetin||DDS (diallyl disulfide)|
|S-methyl-L-cysteine sulfoxide (MCSO)|
Even within this limited chart showing a dozen or so phytonutrients, there are health benefits that stretch across most of our body's organ systems, including our cardiovascular system, endocrine system, digestive system, immune and inflammatory systems, and musculoskeletal system. Of special interest in the health research has been the risk-reducing impact of onion intake on the cardiovascular system.
The health benefits of onion phytonutrients are not yet as well researched as the health benefits of its fellow allium vegetable, garlic. But we suspect that contributions of onion will become better recognized as health research on this beloved allium vegetable moves forward.
Unlike the research on garlic and its cardiovascular benefits, research specifically focused on onion has mostly been conducted on animals rather than humans. In these animal studies, there is some form of onion extract used to test potential health benefits. Interestingly, however, researchers have tried to look specifically at different types of onion extracts (for example, extracts from red versus yellow versus white onions) as well as extracts from cooked versus raw onions. In these animal studies, there is evidence that onion's sulfur compounds may work in an anti-clotting capacity and help prevent the unwanted clumping together of blood platelet cells. There is also evidence showing that sulfur compounds in onion can lower blood levels of cholesterol and triglycerides, and also improve cell membrane function in red blood cells.
Perhaps the most fascinating recent studies in this area involve a group of messaging molecules called oxylipins. Oxylipins are routinely made in the body from polyunsaturated fatty acids. Their very name comes from their origin: "oxy + lipid" can roughly be translated as "fats that have undergone oxidation." Normally, you might jump to the conclusion that oxidized forms of fat are a bad thing. Sometimes this conclusion would be true—for example, when an excessive amount of fat-related tissue along our blood vessel walls becomes oxidized. But in other circumstances, oxidized forms of fat can play a helpful role in our metabolism, and oxylipins can be a great example here.
Some oxylipins fall into the category of what are called the "omega-3 oxylipins." These oxylipins are made from omega-3 fatty acids like alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Consumption of onions has been shown to increase the levels of omega-3 oxylipins in the liver, and this increase in omega-3 oxylipins may help explain the ability of onions to help regulate proper blood fat levels as well as blood levels of cholesterol. We expect to see much more work in this area of onion intake and oxylipin changes. There is a good likelihood that these oxylipin changes may not only be related to our cardiovascular health but also to our ability to maintain good blood sugar regulation and to lower certain obesity-related risks as well.
In human studies, most of the cardiovascular benefits related to onions have not been connected with onions themselves, but with onion-containing diets. This difference is an important one, because in general, it has been difficult for researchers to estimate exactly how much onion study participants have consumed. Onions (like garlic, leeks, chives, and scallion) are often included in relatively small amounts and scattered through a meal plan in the form of sauces, soups, and other combination foods. This "scattered presence" of onions in onion-containing diets has made it difficult for researchers to pinpoint what degree of cardiovascular risk reduction is associated with what level of onion intake.
Before leaving the topic of onion intake and cardio support, it is important to point out the outstanding antioxidant and anti-inflammatory richness of onions. We've seen recent studies attesting to antioxidant benefits in all types of onions including red, yellow, and white. Since chronic oxidative stress and chronic inflammation inside of our blood vessels (especially our arteries) is linked to increased risk of several cardiovascular diseases (for example, atherosclerosis), the proven health benefits of onions for this body system make good sense to us. We have also given this category of onion health benefits (antioxidant and anti-inflammatory) its own special section below.
At the very outset, it is worth remembering that onions are a good source of vitamin C and the mineral manganese, two "conventional" nutrients that play a key role in our body's antioxidant support. With respect to vitamin C, we are talking not only about better protection of genetic materials like RNA and DNA but also protection of many cell structures. Additionally, vitamin C helps Phase 1 ("mixed function oxidase") enzymes in our body's detoxification system function properly because it helps keep metal cofactors for those enzymes in place. With respect to manganese, we are talking about another set of important antioxidant benefits. Heading up this set of benefits would be proper functioning of the enzyme superoxide dismutase (SOD) in a form that requires manganese (abbreviated MnSOD). MnSOD is one of the key enzymes in our mitochondria, cell components that are critical for oxygen-based energy production. Good antioxidant protection in our mitochondria is quite critical since these cell components are so vigorously engaged in oxygen metabolism and can trigger problems unless functioning safely.
However, it's equally important—and perhaps even more important—to recognize the unique antioxidant and anti-inflammatory phytonutrients provided by onions. Perhaps most famous here are the quercetin flavonoids (and quercetin glycosides) that are so plentiful in onions (and especially red onions). Also well studied here are the anthocyanin flavonoids that give red onions their wonderful color. Yet studies also show that yellow and white onions can also be concentrated sources of antioxidant and anti-inflammatory phytonutrients. At the beginning of this Health Benefits section, you will find a chart showing key flavonoids, organic acids, and sulfur-containing compounds in onions. Virtually all of these nutrients have been shown to have antioxidant and anti-inflammatory properties and to be contained in most varieties of onions, including yellow and white varieties. (With the anthocyanin flavonoids, it is a different story, since these flavonoids are only concentrated in red or purple onion varieties.)
While still mostly researched in the lab or in animal studies, some of the unique anti-inflammatory phytonutrients found in onion are especially worth noting. For example, onionin A, a sulfur-containing compound so clearly named after the onion, is a unique anti-inflammatory moledule that is found in the bulb portion (or root) of the onion plant. Onionin A has been shown to inhibit the activity of macrophages, specialized white blood cells that play a key role in our body's immune defense system. Since one of the defense strategies employed by these white blood cells can involve the triggering of large-scale inflammatory responses, overactivity on their part can sometimes be a harmful event if these large-scale responses are not needed. In other words, it is sometimes very helpful to prevent this overactivity. In lab and animal studies, onionin A from the root portion of the onion appears to provide exactly this kind of help.
Most researchers would point to quercetin as the hallmark flavonoid antioxidant and anti-inflammatory substance in onions. The quercetin content of onions is especially well-studied in the case of red onions, which appear to be richer in this compound that either white or yellow varieties. In animal studies, the potential value of quercetin from onions has been especially thought provoking, and you can find more details about this potential value in the final topic ("Other Potential Health Benefits from Onion') addressed in this Health Benefits section.
Several servings of onion each week may be sufficient to statistically lower your risk of some types of cancer. For colorectal, laryngeal, and ovarian cancer, between 1–7 servings of onion per week may provide you with risk reduction. But for decreased risk of oral and esophageal cancer, you are likely to need multiple servings of onions per day. In general, it has been quite difficult for cancer researchers to arrive at strong, indisputable links between cancer risk and levels of allium vegetable intake because it isn't easy for study participants to estimate exactly how many servings of allium vegetables they consumed. Onions, garlic, leeks, chives, scallion, and other allium vegetables are often included in relatively small amounts in sauces, soups, and other combination foods, and in this sense they can become "hidden" in a meal and more difficult to quantify. Overall, we would describe this area of onion health benefits as one in which there are still some significant "research gaps."
An overall take-away from the research at this point in its progression: we believe it makes sense to err on the high side if you want to obtain the full potential cancer-related benefits of onion. For example, while a few slivers of sliced onion on a tossed salad can definitely be a good thing—and tasty as well—they are probably not enough to provide you with the cancer-related onion benefits you are seeking. At WHFoods, we consider 1 cup of cooked, chopped onion to be equivalent to one serving. Our outstanding recommended level of allium vegetable intake is two-thirds of a cup per day. If you were going to obtain this entire outstanding recommended level from onions alone, you would need to consume two-thirds of a cup of onion per day. (Of course, there are other outstanding allium vegetables that can help you meet this recommended intake level for allium vegetables, including garlic and leeks.) Still, whenever you believe that onion might make a tasty addition to a soup, sauce, salad, or entrée, consider adding the equivalent of one whole medium-sized onion, rather than some far smaller portion. And for a great example of a well-balanced diet that includes onions every day of the week in a serving equivalent of two-thirds of a cup, take a look at our 7-Day Menu. You will also find both red and yellow onions included in our 7-Day Menu in a way that perfects the flavors and textures in the recipes, as well as the appearance of the recipes when served.
In animal studies, onions have shown potential for improvement of blood sugar balance, even though it is not yet clear about the carry over of these benefits for humans who are seeking better blood sugar balance from their diet. Most of the animal studies have been conducted on laboratory rats, and most have used onion juice or onion extract as the form of onion tested. Future research is needed to clarify onion's potential for helping lower blood sugar and improving blood sugar control, especially in persons with blood sugar problems. However, one exciting new line of evidence in this area involves the impact of quercetin from onion on skeletal muscle, mitochondrial metabolism, and insulin sensitivity. The configuration of events hypothesized by researchers is as follows: first, it is possible that the impact of quercetin initially takes place at a genetic level, or more specifically, on the way in which gene activities are regulated. Here the focus has been on a molecule called peroxisome proliferation activated-receptor gamma coactivator 1 alpha (or Pcg-1α). Through their impact on Pcg-1α, components in onion may be able to improve mitochondrial function in skeletal muscle, thereby improving events related to healthy mitochondrial function, including insulin sensitivity and glucose tolerance. There is also a very likely connection here to risk of obesity, since skeletal muscle metabolism, mitochondrial metabolism, insulin sensitivity, glucose tolerance, and risk of obesity are closely related in health research.
While not as well researched as garlic in terms of antibacterial benefits, onion has nevertheless been shown to help prevent bacterial infection. Along with its sulfur-containing compounds, the flavonoid quercetin contained in onion helps provide these antibacterial benefits. We've seen studies showing antibacterial activity of onion in relationship to the bacteria Streptococcus mutans and Streptococcus sobrinus. (These bacteria are commonly involved in the production of tooth cavities). Antibacterial benefits have also been shown in the area of gum (periodontal) disease bacteria, including Porphyromonas gingivalis and Prevotella intermedia. Interestingly, in one study, fresh, chopped, uncooked onion had antibacterial effects on these potentially unwanted gum bacteria, but non-fresh, uncooked onion (raw onion that was chopped and then left to sit for 2 days at room temperature) did not demonstrate these same antibacterial properties nor did fresh onion that was grated and then steamed for 10 minutes. While it is not possible to draw broad conclusions from a single lab study, these findings suggest that length of storage (for onion that has been chopped but not cooked) and duration of heat exposure (in this case involving exposure to steam for 10 full minutes) can affect some of onion's health benefits. For these reasons, special care may be needed in the storage, handling, and cooking of this allium vegetable.
While we may not usually think about them in this way, onions are a food of astonishing diversity. They are enjoyed in virtually all parts of the world—and so much so that you will find countries in Asia (including China and India), Southeast Asia (including Indonesia and Myanmar), the Middle East (like Turkey and Iran), South America (Brazil), and Russia all being included among the major onion-producing countries of the world. But even this level of diversity fails to tell the full story, since the top onion-consuming countries in the world are also found in North America (the United States), Northern Africa (Libya and Algeria), and Europe (the United Kingdom and France).
Given this remarkable diversity, it is also not surprising that onions can be classified in so many different ways. In the grocery store, perhaps the most common classification system is by color. It is easy to recognize the difference between reds and yellows and whites (at least when considering the root portion of the onions (bulbs).
By contrast, the color green is typically used not to describe the root/bulb portion of the plant. Instead, "green onion" is a term usually used to refer to the stalk portion of the plant. However, this term is often used quite loosely, and it can gloss over some interesting underlying differences that can take place in the world of "green onions." Many varieties of onions that will eventually form a large bulb can be harvested quite early in the growth process so that the large bulb has not had time to form. Sometimes you will find early harvested onions being sold as "green onions." Other varieties of onions either form a very small bulb regardless of their age, or they even never form a bulb at all.
You may also find these varieties being sold in the grocery as "green onions." When varieties only form a very small bulb or no bulb at all, they are typically also described as "bunching onions" as well as "scallions." Different plant experts use this term "scallions" in different ways, however, and some experts only use the word "scallion" if the onion variety is non-bulb-forming. All of the varieties referred to above fall into the same scientific genus/species of Allium cepa. In addition, most of the varieties referred to above fall into the subspecies Allium cepa var cepa.
Two further important notes about "green onions." First, they are not always green! Apache onions, for example, are scallions with bright green stalks and very small vibrant purple/red bulb portions. Second, "green onions" also include one species not described above, namely Allium fistulosum. Green onions in this group are often referred to either as Welsh onions or Japanese bunching onions.
Shallots (Allium cepa var. ascalonicum), as you will find them in the grocery, are sometimes confused with garlic. That's because the dried bulb portion of the plant is what you typically see on display, and this variety of onion forms a cluster of small bulbs instead of one single bulb. So this dried cluster of bulbs can look like a bulb of garlic with its collection of cloves. Still, as you can see from their science name, shallots belong to the exact same genus and species of plant (Allium cepa) as all of the onions described above.
Onions can also be classified according to differences in taste. The basic dividing line here is between strong flavored and mild/sweet. As a very general rule, the softer varieties of onion are milder and sweeter in taste and the harder varieties are more pungent and strongly flavored. This distinction between strong/pungent and mild/sweet can sometimes overshadow distinctions involving color. For example, you may hear the term "sweet onions" being used to differentiate these varieties from either yellow or red or white onions.
Taste differences in onions may sometimes be related to day length. In the United States, for example, "long-day" onions commonly grown in Washington, Illinois, and New York often include well-known (and much loved) sweet varieties. "Intermediate-day" onions grown in Northern California and Colorado also include many sweet varieties. "Short-day" onions more common to southern California, southern Texas, and southern Georgia tend to have fewer representatives in the sweetness category, but there are also plenty of exceptions. For example, the pungency of onions is not only related to day length but also to many other factors including the mildness of the climate and the mineral content of the soil. In some areas with heavy annual rainfall, for example, sulfur can be leached out of the soil in amounts conducive to the creation of sweet onions. One famous example here are Vidalia onions grown in the southern half of Georgia.
You may also hear onions being referred to as "early bulb" or "late bulb." Like this terminology suggests, the varieties involved differ in their speed of bulb formation.
Onions varieties can differ in their perishability, and this perishability is not always predictable based on color, taste, or other easily-detected differences. For example, we have come across research studies on one variety of red onions called "Breme" onions that are only grown on a 25-acre plot of land in northwestern Italy and that are only distributed locally, partially due to their delicate nature. Of course, most of the onions that you will find in the supermarket are not highly perishable in this same way and do not need to be used right away unless they are cut open. For cut, chopped, and diced onions, we always recommend refrigeration in a covered container and use the next day, or two days later at the most.
As you can see from all of the examples above, geography, climate, and timing can make for important differences in the life of an onion, and these types of impacts may be particularly true for sweet onions. It is perhaps for this reason that some sweet onions are very closely linked to a very limited season of harvest. Maui Sweet Onions are known for their peak season between April and June, Vidalia onions for their peak season between April and late August, and Walla Walla Sweets for their peak season between mid-June and mid-August.
Specific varieties of red onions that you might find at a farmer's market or in a supermarket include Redwing, Red River, Red Zeppelin, Red Creole, Southern Belle Red, Red Grano, Red Granex, and California Early Red. Yellow varieties include Yellow Sweet Spanish, Fiesta, Stockton Yellow Globe, Highlander, Copra, and Texas Legend. White varieties include Sterling, Texas Early White, and Ringmaster White Spanish.
As mentioned earlier in the Description section, onions are a remarkable food in terms of their worldwide geography, and this feature of onions is quickly visible in their history. Most researchers point to Central Asia as the original birthplace of onions; included in this area would be the present-day countries of Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan, and Afghanistan. Along with the countries of Northern Africa—including Algeria, Morocco, and Egypt—these Central Asian countries still serve as one of the largest onion-growing regions in the world. However, joining these countries as major onion producers have been countries like Myanmar and South Korea in southeast Asia, as well as Brazil in South America and the United States in North America. In fact, today it has become somewhat difficult to find a widely adopted cuisine that does not feature onions in some form or other.
Within the United States, California is by far the largest onion-producing state, followed by Washington, Oregon, Texas, and Georgia. At the same time, however, onions are now grown commercially in over 15 different states. And while far more onions are consumed per capita in the countries of Libya, Albania, Tajikistan, Uzbekistan, and Algeria than in the United States, the U.S. still ranks in the world's Top 10 onion-consuming countries, and in some surveys, onions rank as the third most consumed vegetables in terms of volume, following tomatoes and potatoes. (Here it would be important to note, however, that consumption of these vegetables does not necessarily mean that they have been consumed in their fresh, whole food form.) Research estimate suggest that in the U.S., the average per capita intake of onions in all forms is about 25 pounds per year, or roughly ½ pound per week.
On a worldwide basis, the top onion-producing countries in the world include China, India, the United States, Iran, Turkey, Egypt, Pakistan, Bangladesh, Indonesia, Myanmar, Russia, and Brazil.
Choose onions that are clean, well shaped, have no opening at the neck, and feature crisp, dry outer skins. Avoid those that are sprouting or have signs of mold. In addition, onions of inferior quality often have soft spots, moisture at their neck, and dark patches, which may all be indications of decay. As conventionally grown onions are often irradiated to prevent them from sprouting, purchase organically grown varieties whenever possible to avoid onions that have undergone this process. When purchasing scallions, look for those that have green, fresh-looking tops that appear crisp yet tender. The base should be whitish in color for two or three inches. Avoid those that have wilted or yellowed tops.
At WHFoods, we encourage the purchase of certified organically grown foods, and onions are no exception. Repeated research studies on organic foods as a group show that your likelihood of exposure to contaminants such as pesticides and heavy metals can be greatly reduced through the purchased of certified organic foods, including onions. In many cases, you may be able to find a local organic grower who sells onions but has not applied for formal organic certification either through the U.S. Department of Agriculture (USDA) or through a state agency. (Examples of states offering state-certified organic foods include California, New York, Oregon, Vermont, and Washington.) However, if you are shopping in a large supermarket, your most reliable source of organically grown onions is very likely to be onions that display the USDA organic logo.
Onions should be stored in a well ventilated space at room temperature, away from heat and bright light. With the exception of green onions, do not refrigerate onions. Place them in a wire hanging basket or a perforated bowl with a raised base so that air can circulate underneath. The length of storage varies with the type of onion. Those that are more pungent in flavor, such as yellow onions, should keep for about a month if stored properly. They will keep longer than those with a sweeter taste, such as white onions, since the compounds that confer their sharp taste help to preserve them. Scallions should be stored in a plastic bag in the refrigerator where they will keep for about one week. All onions should be stored away from potatoes, as they will absorb their moisture and ethylene gas, causing them to spoil more readily.
Store cut onions by placing in a sealed container; use them within a day or two at the very most since they tend to oxidize and lose their nutrient content rather quickly. Cooked onions will best maintain their taste in an airtight container where they can be kept for a few days; they should never be placed in a metal storage container as this may cause them to discolor. Although peeled and chopped onions can be frozen (without first being blanched), this process will cause them to lose some of their flavor.
If you'd like even more recipes and ways to prepare onions the Nutrient-Rich Way, you may want to explore The World's Healthiest Foods book.
Onions, chopped, cooked
|biotin||7.98 mcg||27||5.2||very good|
|vitamin B6||0.27 mg||16||3.1||good|
|vitamin C||10.92 mg||15||2.8||good|
|vitamin B1||0.09 mg||8||1.5||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%