What's New and Beneficial About Onions

• Sofrito sauce—typically associated with Spanish cuisine but actually used in a variety of cuisines worldwide—has been the topic of a recent study that provides some fascinating new information about onions. The four sauce ingredients in this study represented some of our very favorite foods: extra virgin olive oil, garlic, onions, and tomatoes. In this study, several methods for preparation of the sofrito sauce were investigated, but one of the consistent study findings was the ability of onion to help increase the bioavailability of lycopene (a well-studied, health-promoting carotenoid) from the tomatoes. The authors speculated that the sulfur-compounds in the onions may have been involved in a chemical reaction (electron transfer) that helped increase the availability of the lycopene. We feature many recipes on our website that include both onions and tomatoes—including frittatas, soups, salads, and entrees. You can use our Recipe Assistant to search for and look over all of them.
• The flavonoids in onion tend to be more concentrated in the outer layers of the flesh. To maximize your health benefits, peel off as little of the fleshy, edible portion as possible when removing the onion's outermost paper layer. Even a small amount of "overpeeling" can result in unwanted loss of flavonoids. For example, a red onion can lose about 20% of its quercetin and almost 75% of its anthocyanins if it is "overpeeled."
• Recent research is prompting health researchers to consider a potential set of new connections between onion intake, blood fat levels, and overall handling of cholesterol and fats by the liver. This research involves a group of messaging molecules called oxylipins. Oxylipins are routinely made in the body from polyunsaturated fatty acids, and they include what are called the "omega-3 oxylipins" made from omega-3 fatty acids like alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). Very broadly speaking, oxylipins can be grouped into categories like HODE, HEPE, HETE, or HOTrE. 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. Although decreased risk of oxidative stress and chronic inflammation in the blood vessels has previously been shown to be a welcomed result of onion intake, this recent research on oxylipins may lead to a better understanding of onions and their unique health benefits.
• The total polyphenol content of onions is much higher than many people expect. (Polyphenols are one of the largest categories of phytonutrients in food. This category includes all flavonoids as well as tannins.) The total polyphenol content of onion is not only higher than its fellow allium vegetables, garlic and leeks, but also higher than tomatoes, carrots, and red bell pepper. In the French diet, only six vegetables (artichoke heart, parsley, Brussels sprouts, shallot, broccoli, and celery) have a higher polyphenol content than onion. Since the French diet has been of special interest to researchers in terms of disease prevention, onion's strong polyphenol contribution will very likely lead to follow-up studies that pay closer attention to this unique allium vegetable.
• Within the polyphenol category, onions are also surprisingly high in flavonoids. For example, on an ounce-for-ounce basis, onions rank in the top 10 of commonly eaten vegetables in their quercetin content. The flavonoid content of onions can vary widely, depending on the exact variety and growing conditions. Although the average onion is likely to contain less than 100 milligrams of quercetin per 3-1/2 ounces, some onions do provide this amount. And while 100 milligrams may not sound like a lot, in the United States, moderate vegetable eaters average only twice this amount for all flavonoids (not just quercetin) from all vegetables per day. We are also happy to report that there is a new flavonoid on the block, and that flavonoid is called fisetin. Of course, fisetin has always been a component of foods—it just hasn't been well-studied by scientists until very recently. Onions turn out to be a great vegetable choice for obtaining fisetin. (The most concentrated food options here appear to be fruits, especially strawberries). What we like about this new information on onions and fisetin is the reassurance that it gives us about the uniqueness of onions as a source of flavonoids.
• If you are slicing or dicing onions and not planning to use them until the next day, make sure to place them in the refrigerator in a closed container for increased safety. We've seen a recent study showing potential growth of E. coli 0157:H7 and Salmonella enterica in diced yellow onions that were kept non-refrigerated for a period of 1 or more days. However, refrigeration of the chopped yellow onions (at a temperature of 39°F/4°C) was found to prevent growth of both bacteria. In general, we always recommend the use of chopped fresh vegetables during recipe preparation rather than chopping vegetables "ahead of time" and storing them in chopped form. With fresh vegetables, chopping is considered as a type of "wounding stress" when looked upon in terms of food chemistry. Especially at room temperature, chopping can result in metabolic changes including increased respiration rate and loss of certain nutrients—for example, vitamin C.
• For a great example of a well-balanced diet that includes onions every day of the week, look no further than our World's Healthiest Foods Meal Plan. On some days, you will find onions being included in two different recipes, and not only are they included, but we have included them in such a way as to bring out the very best in our World's Healthiest Foods Meal Plan Recipes. You will also find both red and yellow onions being included in our World's Healthiest Foods Meal Plan in a way that perfects the flavors and textures in our World's Healthiest Foods Meal Plan Recipes - as well as the appearance of those recipes when served.

WHFoods Recommendations

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.

This chart graphically details the %DV that a serving of Onions provides for each of the nutrients of which it is a good, very good, or excellent source according to our Food Rating System. Additional information about the amount of these nutrients provided by Onions can be found in the Food Rating System Chart. A link that takes you to the In-Depth Nutritional Profile for Onions, featuring information over 80 nutrients, can be found under the Food Rating System Chart.

• Health Benefits
• Description
• History
• How to Select and Store
• Tips for Preparing and Cooking
• How to Enjoy
• Nutritional Profile
• References

Health Benefits

Onions Are Rich in Conventional Nutrients As Well As Unique Phytonutrients

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)
		onionin A

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.

Cardiovascular Benefits of Onions

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.

Antioxidant and Anti-Inflammatory Benefits of Onions

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.

Potential Cancer Protection From Onions

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.

Other Potential Health Benefits From Onions

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.

Description

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.

History

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.

How to Select and Store

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 sealed container in the refrigerator where they will keep for about one week. All onions should be stored away from potatoes, since moisture and ethylene gas from the potatoes can cause them to spoil more readily.

Store cut raw onions by placing in a sealed container. Use them within a day or two at the most to prevent loss of quality. Cooked onions will best maintain their taste in an airtight container where they can be kept for a few days. They should not be placed in a metal storage container because this method can cause discoloration. Although peeled and chopped onions can be frozen (without first being blanched), this practice may cause them to lose some of their flavor.

Tips for Preparing and Cooking

Cut onions into 1/4-inch slices to cook them evenly and quickly.

While many people love to eat onions, they sometimes dread cutting them since this process can cause the eyes to water profusely. The substance that triggers this reaction is a special gas that has been named lachrymatory factor (LF). (The full chemical name for this gas is propanethial S-oxide, and it is made from a naturally occurring compound in onion called 1-propenyl-L-cysteine sulphoxide.) Recent research has shown that LF gas is not produced through activity of onion's alliinase enzyme, but rather through the activity of a special enzyme named lachrymatory-factor synthase. Interestingly, even though lachrymatory-factor synthase is the enzyme responsible for production of LF gas, the alliinase enzyme must still be present in order for LF gas production to occur.

If cutting onions irritates your eyes, there are a few tricks that you can try. Use a very sharp knife and always cut the onions while standing - in that way your eyes can be further away from the onions. Consider cutting onions by an open window. If you chill the onions for an hour or so before cutting, you may be able to slow down the onion's metabolism and thereby lessen the rate of LF gas production. Cutting onions under cold, running water is another possible step. If none of these options work, you might also consider wearing safety glasses or goggles.

The Nutrient-Rich Way of Cooking Onions

Although onions are most often used as a seasoning, we want to share with you how to enjoy them as a healthy side dish. For great flavor and nutrition we recommend Healthy Sautéeing sliced onions.

Healthy Sauté - similar to Quick Boiling and Quick Steaming, our other recommended cooking methods - follows three basic cooking guidelines that are generally associated in food science research with improved nutrient retention. These three guidelines are: (1) minimal necessary heat exposure; (2) minimal necessary cooking duration; (3) minimal necessary food surface contact with cooking liquid.

Heat 2 TBS vegetable or chicken broth over medium heat in a stainless steel skillet. When broth begins to steam, add onions and cover for 3 minutes. The onions will release a small amount of liquid. Uncover, add another 2 TBS broth, and continue to stir for 4 minutes, leaving the lid off. Toss with our Mediterranean Dressing and top with your favorite optional ingredients. For details see, 7-Minute Healthy Sautéed Onions.

How to Enjoy

A Few Quick Serving Ideas

• Combine chopped onions, tomatoes, avocado, and jalapeno for an all-in-one guacamole salsa dip.
• To perk up plain rice, top with green onions (scallions) and sesame seeds.
• Healthy Sauteed chopped onions can enhance the flavor or almost any vegetable dish.
• Enjoy a classic Italian salad—sliced onions, tomatoes, and mozzarella cheese drizzled with olive oil.

WHFoods Recipes that Feature Onions

• 5 Spice Onion Soup
• 7-Minute Healthy Sautéed Onions

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.

Nutritional Profile

The outstanding polyphenol content of onions (including their rich concentration of flavonoid polyphenols) is probably the most overlooked nutrient category of this allium vegetable. Among the flavonoids, onions also provide a particularly large amount of quercetin. A wide variety of allyl sulfides are found in onion, including the four major diallyl sulfides: DMS (diallyl monosulfide), DDS (diallyl disulfide), DTS (diallyl trisulfide), and DTTS (diallyl tetrasulfide). Also present are a wide variety of sulfoxides, including (+) S-methyl-L-cysteine sulfoxide (MCSO), (+)-S-(1-propenyl)-L-cysteine sulfoxide (PRENCSO), S-methyl-l-cysteine sulfoxide, S-propyl-l-cysteine sulfoxide, and S-propenyl-l-cysteine sulfoxide.

Onions are a very good source of biotin. They are also a good source of manganese, vitamin B6, copper, vitamin C, dietary fiber, phosphorus, potassium, folate and vitamin B1.

Introduction to Food Rating System Chart

In order to better help you identify foods that feature a high concentration of nutrients for the calories they contain, we created a Food Rating System. This system allows us to highlight the foods that are especially rich in particular nutrients. The following chart shows the nutrients for which this food is either an excellent, very good, or good source (below the chart you will find a table that explains these qualifications). If a nutrient is not listed in the chart, it does not necessarily mean that the food doesn't contain it. It simply means that the nutrient is not provided in a sufficient amount or concentration to meet our rating criteria. (To view this food's in-depth nutritional profile that includes values for dozens of nutrients - not just the ones rated as excellent, very good, or good - please use the link below the chart.) To read this chart accurately, you'll need to glance up in the top left corner where you will find the name of the food and the serving size we used to calculate the food's nutrient composition. This serving size will tell you how much of the food you need to eat to obtain the amount of nutrients found in the chart. Now, returning to the chart itself, you can look next to the nutrient name in order to find the nutrient amount it offers, the percent Daily Value (DV%) that this amount represents, the nutrient density that we calculated for this food and nutrient, and the rating we established in our rating system. For most of our nutrient ratings, we adopted the government standards for food labeling that are found in the U.S. Food and Drug Administration's "Reference Values for Nutrition Labeling." Read more background information and details of our rating system.

In-Depth Nutritional Profile

In addition to the nutrients highlighted in our ratings chart, here is an in-depth nutritional profile for Onions. This profile includes information on a full array of nutrients, including carbohydrates, sugar, soluble and insoluble fiber, sodium, vitamins, minerals, fatty acids, amino acids and more.

Onions, chopped, cooked (Note: "--" indicates data unavailable)
1.00 cup (210.00 g)	GI: low
BASIC MACRONUTRIENTS AND CALORIES
nutrient	amount	DRI/DV (%)
Protein	2.86 g	6
Carbohydrates	21.31 g	9
Fat - total	0.40 g	1
Dietary Fiber	2.94 g	11
Calories	92.40	5
MACRONUTRIENT AND CALORIE DETAIL
nutrient	amount	DRI/DV (%)
Carbohydrate:
Starch	-- g
Total Sugars	9.93 g
Monosaccharides	7.62 g
Fructose	3.02 g
Glucose	4.60 g
Galactose	0.00 g
Disaccharides	2.31 g
Lactose	0.00 g
Maltose	0.00 g
Sucrose	2.31 g
Soluble Fiber	1.05 g
Insoluble Fiber	1.89 g
Other Carbohydrates	8.44 g
Fat:
Monounsaturated Fat	0.06 g
Polyunsaturated Fat	0.15 g
Saturated Fat	0.07 g
Trans Fat	0.00 g
Calories from Fat	3.59
Calories from Saturated Fat	0.59
Calories from Trans Fat	0.00
Cholesterol	0.00 mg
Water	184.51 g
MICRONUTRIENTS
nutrient	amount	DRI/DV (%)
Vitamins
Water-Soluble Vitamins
B-Complex Vitamins
Vitamin B1	0.09 mg	8
Vitamin B2	0.05 mg	4
Vitamin B3	0.35 mg	2
Vitamin B3 (Niacin Equivalents)	1.05 mg
Vitamin B6	0.27 mg	16
Vitamin B12	0.00 mcg	0
Biotin	7.98 mcg	27
Choline	14.28 mg	3
Folate	31.50 mcg	8
Folate (DFE)	31.50 mcg
Folate (food)	31.50 mcg
Pantothenic Acid	0.24 mg	5
Vitamin C	10.92 mg	15
Fat-Soluble Vitamins
Vitamin A (Retinoids and Carotenoids)
Vitamin A International Units (IU)	4.20 IU
Vitamin A mcg Retinol Activity Equivalents (RAE)	0.21 mcg (RAE)	0
Vitamin A mcg Retinol Equivalents (RE)	0.42 mcg (RE)
Retinol mcg Retinol Equivalents (RE)	0.00 mcg (RE)
Carotenoid mcg Retinol Equivalents (RE)	0.42 mcg (RE)
Alpha-Carotene	0.00 mcg
Beta-Carotene	2.10 mcg
Beta-Carotene Equivalents	2.10 mcg
Cryptoxanthin	0.00 mcg
Lutein and Zeaxanthin	8.40 mcg
Lycopene	0.00 mcg
Vitamin D
Vitamin D International Units (IU)	0.00 IU	0
Vitamin D mcg	0.00 mcg
Vitamin E
Vitamin E mg Alpha-Tocopherol Equivalents (ATE)	0.04 mg (ATE)	0
Vitamin E International Units (IU)	0.06 IU
Vitamin E mg	0.04 mg
Vitamin K	1.05 mcg	1
Minerals
nutrient	amount	DRI/DV (%)
Boron	-- mcg
Calcium	46.20 mg	5
Chloride	12.60 mg
Chromium	-- mcg	--
Copper	0.14 mg	16
Fluoride	-- mg	--
Iodine	4.20 mcg	3
Iron	0.50 mg	3
Magnesium	23.10 mg	6
Manganese	0.32 mg	14
Molybdenum	-- mcg	--
Phosphorus	73.50 mg	11
Potassium	348.60 mg	7
Selenium	1.26 mcg	2
Sodium	6.30 mg	0
Zinc	0.44 mg	4
INDIVIDUAL FATTY ACIDS
nutrient	amount	DRI/DV (%)
Omega-3 Fatty Acids	0.01 g	0
Omega-6 Fatty Acids	0.15 g
Monounsaturated Fats
14:1 Myristoleic	0.00 g
15:1 Pentadecenoic	0.00 g
16:1 Palmitol	0.00 g
17:1 Heptadecenoic	0.00 g
18:1 Oleic	0.06 g
20:1 Eicosenoic	0.00 g
22:1 Erucic	0.00 g
24:1 Nervonic	0.00 g
Polyunsaturated Fatty Acids
18:2 Linoleic	0.15 g
18:2 Conjugated Linoleic (CLA)	-- g
18:3 Linolenic	0.01 g
18:4 Stearidonic	0.00 g
20:3 Eicosatrienoic	0.00 g
20:4 Arachidonic	0.00 g
20:5 Eicosapentaenoic (EPA)	0.00 g
22:5 Docosapentaenoic (DPA)	0.00 g
22:6 Docosahexaenoic (DHA)	0.00 g
Saturated Fatty Acids
4:0 Butyric	0.00 g
6:0 Caproic	0.00 g
8:0 Caprylic	0.00 g
10:0 Capric	0.00 g
12:0 Lauric	0.00 g
14:0 Myristic	0.00 g
15:0 Pentadecanoic	0.00 g
16:0 Palmitic	0.06 g
17:0 Margaric	0.00 g
18:0 Stearic	0.00 g
20:0 Arachidic	0.00 g
22:0 Behenate	0.00 g
24:0 Lignoceric	0.00 g
INDIVIDUAL AMINO ACIDS
nutrient	amount	DRI/DV (%)
Alanine	0.08 g
Arginine	0.38 g
Aspartic Acid	0.16 g
Cysteine	0.05 g
Glutamic Acid	0.46 g
Glycine	0.12 g
Histidine	0.05 g
Isoleucine	0.10 g
Leucine	0.10 g
Lysine	0.14 g
Methionine	0.02 g
Phenylalanine	0.07 g
Proline	0.09 g
Serine	0.08 g
Threonine	0.07 g
Tryptophan	0.04 g
Tyrosine	0.07 g
Valine	0.07 g
OTHER COMPONENTS
nutrient	amount	DRI/DV (%)
Ash	0.92 g
Organic Acids (Total)	-- g
Acetic Acid	-- g
Citric Acid	-- g
Lactic Acid	-- g
Malic Acid	-- g
Taurine	-- g
Sugar Alcohols (Total)	-- g
Glycerol	-- g
Inositol	-- g
Mannitol	-- g
Sorbitol	-- g
Xylitol	-- g
Artificial Sweeteners (Total)	-- mg
Aspartame	-- mg
Saccharin	-- mg
Alcohol	0.00 g
Caffeine	0.00 mg
Note: The nutrient profiles provided in this website are derived from The Food Processor, Version 10.12.0, ESHA Research, Salem, Oregon, USA. Among the 50,000+ food items in the master database and 163 nutritional components per item, specific nutrient values were frequently missing from any particular food item. We chose the designation "--" to represent those nutrients for which no value was included in this version of the database.

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