Onion Nutrition Facts: Complete Guide to Red, Yellow, and White Onions

Onions are nutrient-dense vegetables packed with antioxidants, vitamins, and beneficial plant compounds. Whether you prefer red, yellow, or white varieties, onions offer impressive health benefits including supporting heart health, regulating blood sugar, and potentially reducing cancer risk.

As one of the most widely consumed vegetables worldwide, onions (Allium cepa) belong to the allium family alongside garlic, leeks, and shallots. These bulbous vegetables can be enjoyed raw, cooked, or pickled, making them an incredibly versatile addition to any diet.

This comprehensive guide explores the complete nutritional profile of different onion varieties, their health benefits, and what you should know before adding more onions to your meals.

Complete Nutritional Profile of Onions

Onions are remarkably low in calories while providing essential nutrients. Understanding their nutritional composition helps you make informed dietary choices.

Yellow Onion Nutrition Facts

Yellow onions are the most common variety and offer impressive nutritional value. Per 3.5 ounces (100 grams) of raw yellow onions, you get:

• Calories: 38-40
• Water content: 89-90%
• Protein: 0.8-1.1 grams
• Carbohydrates: 8.6-9.3 grams
• Natural sugars: 5.8-6.2 grams
• Dietary fiber: 1.7-1.9 grams
• Fat: 0.1 grams

Yellow onions contain higher levels of sulfur compounds, giving them a more pungent flavor. They’re rich in antioxidants, particularly quercetin, which becomes more concentrated when cooked.

Red Onion Nutrition Facts

Red onions have a similar macronutrient profile to yellow onions but contain unique antioxidants. Per 3.5 ounces (100 grams) of raw red onions:

• Calories: 37-42
• Protein: 0.9-1.2 grams
• Carbohydrates: 8.3-9.0 grams
• Fiber: 1.5-1.8 grams
• Sugar: 5.5-6.0 grams
• Fat: 0.1 grams

Red onions stand out due to their high anthocyanin content—the same powerful antioxidants found in berries and red wine. These compounds give red onions their distinctive purple-red color and provide enhanced antioxidant protection compared to other varieties.

White Onion Nutrition

White onions have a milder, slightly sweeter taste and comparable nutrition to their colored counterparts:

• Calories: 38-40
• Carbohydrates: 8.5-9.2 grams
• Fiber: 1.6-1.9 grams
• Protein: 0.8-1.0 grams

White onions contain slightly less quercetin than yellow onions but are still nutritious and offer similar health benefits.

Essential Vitamins and Minerals in Onions

All onion varieties provide important micronutrients that support various bodily functions:

Vitamin C

Onions contain approximately 7-12 mg of vitamin C per 100 grams, providing about 8-13% of the daily recommended intake. This essential antioxidant supports immune function, collagen production, and iron absorption.

B Vitamins

Onions offer several B vitamins including:

• Folate (B9): Essential for DNA synthesis and cell division, particularly important during pregnancy
• Vitamin B6 (Pyridoxine): Supports metabolism, brain health, and red blood cell formation
• Thiamine (B1): Helps convert nutrients into energy

Potassium

With approximately 146 mg per 100 grams, onions contribute to your daily potassium needs. This mineral helps regulate blood pressure, supports proper muscle function, and maintains fluid balance.

Manganese

Onions provide trace amounts of manganese, which plays a role in bone formation, wound healing, and metabolism.

Powerful Plant Compounds in Onions

Beyond basic nutrition, onions contain bioactive compounds that contribute significantly to their health benefits.

Quercetin

This flavonoid antioxidant is highly concentrated in onions, particularly yellow and red varieties. Quercetin has been studied for its anti-inflammatory properties and potential to support cardiovascular health by helping maintain healthy blood pressure levels.

Anthocyanins (Red Onions)

Exclusive to red and purple onions, anthocyanins are powerful antioxidants that may help protect cells from oxidative damage. Research suggests these compounds may support heart health and cognitive function.

Organosulfur Compounds

Onions contain various sulfur compounds including:

• Allyl sulfides: May support cardiovascular health
• Thiosulfinates: Possess antimicrobial properties
• Sulfoxides: Contribute to onion’s characteristic flavor and potential health benefits

These sulfur compounds are released when onions are cut or crushed, creating the pungent aroma and causing tears.

Fructooligosaccharides (Prebiotics)

Onions are rich in fructans, a type of prebiotic fiber that feeds beneficial gut bacteria. A healthy gut microbiome supports digestion, immune function, and may influence mood and mental health.

Carbohydrates and Fiber Content

Onions contain approximately 9-10% carbohydrates by weight, consisting of both simple sugars and complex carbohydrates.

Natural Sugars

The natural sweetness of onions comes from glucose, fructose, and sucrose. Sweet onion varieties like Vidalia or Walla Walla contain higher sugar concentrations, making them ideal for caramelizing.

Dietary Fiber

With about 1.7-1.9 grams of fiber per 100 grams, onions provide both soluble and insoluble fiber. Soluble fiber helps regulate blood sugar and cholesterol levels, while insoluble fiber promotes digestive health.

Net Carbs

For those monitoring carbohydrate intake, the net carbs (total carbs minus fiber) in onions are approximately 7-7.5 grams per 100 grams, making them relatively low-carb vegetable option.

Evidence-Based Health Benefits of Onions

Scientific research has identified numerous potential health benefits associated with regular onion consumption.

Blood Sugar Management

Studies indicate that onions may help regulate blood sugar levels. The sulfur compounds and quercetin in onions appear to have blood sugar-modulating effects.

Research involving people with type 2 diabetes found that consuming 100 grams of raw onion daily resulted in significant reductions in fasting blood sugar levels. The chromium content in onions may also support insulin function.

However, individuals with diabetes should consult their healthcare provider before making significant dietary changes, as onions should complement, not replace, prescribed treatments.

Heart Health Support

Onions contain multiple compounds that may benefit cardiovascular health:

• Quercetin: May help maintain healthy blood pressure levels and reduce inflammation in blood vessels
• Organosulfur compounds: May help reduce blood lipid levels
• Antioxidants: Protect against oxidative stress that can damage blood vessels

Regular consumption of allium vegetables, including onions, has been associated with better cardiovascular health markers in observational studies.

Bone Density and Strength

Research suggests onions may support bone health, particularly in older adults and postmenopausal women who face increased osteoporosis risk.

A large observational study found that women over 50 who consumed onions regularly had greater bone density compared to those who rarely ate them. Onions appear to reduce oxidative stress and may help minimize bone mineral loss.

Antioxidant Protection

Onions rank highly among vegetables for antioxidant content. These antioxidants help neutralize harmful free radicals that contribute to aging and chronic disease.

Red onions provide the highest antioxidant levels due to their anthocyanin content, followed by yellow and white varieties. The antioxidant capacity remains significant even after cooking, though raw onions generally retain more antioxidants.

Cancer Risk Reduction

Population studies have observed associations between higher intake of allium vegetables and reduced risk of certain cancers, particularly stomach and colorectal cancers.

The sulfur compounds and flavonoids in onions possess properties that may help protect cells. However, it’s important to note that eating onions should be part of an overall healthy lifestyle rather than viewed as a specific cancer prevention strategy.

Antimicrobial Properties

Onions have demonstrated antibacterial and antifungal effects in laboratory studies. The sulfur compounds, particularly thiosulfinates, show activity against various harmful microorganisms including certain strains of bacteria and fungi.

Digestive Health

The prebiotic fiber in onions supports digestive health by nourishing beneficial gut bacteria. These bacteria produce short-chain fatty acids that support colon health and may reduce inflammation in the digestive tract.

Anti-Inflammatory Effects

Chronic inflammation contributes to many health conditions. The quercetin and other antioxidants in onions possess anti-inflammatory properties that may help reduce inflammatory markers in the body.

Comparing Red, Yellow, and White Onions

While all onion varieties offer health benefits, each has unique characteristics:

Red Onions

• Highest antioxidant content due to anthocyanins
• Milder, slightly sweet flavor—ideal for raw consumption
• Best for salads, sandwiches, and garnishes
• Most colorful option with distinctive purple-red hue

Yellow Onions

• Highest quercetin levels, especially when cooked
• Strong, pungent flavor that mellows with cooking
• Most versatile for cooking—excellent for caramelizing
• Longer shelf life than other varieties

White Onions

• Milder flavor with slight sharpness
• Crisp texture—popular in Mexican cuisine
• Good for both raw and cooked applications
• Slightly less quercetin than yellow onions

How Cooking Affects Onion Nutrition

Cooking methods significantly impact onion nutrition and health benefits.

Raw Onions

Raw onions retain maximum vitamin C and certain antioxidants. However, some people find raw onions difficult to digest, and the strong flavor can be overwhelming.

Cooked Onions

While cooking reduces some heat-sensitive nutrients like vitamin C, it offers benefits:

• Increases bioavailability of certain antioxidants like quercetin
• Easier to digest for many people
• Reduces the pungent compounds that cause eye irritation and breath odor
• Creates different beneficial compounds through chemical changes

Best Cooking Methods

Research indicates that baking and grilling preserve the most antioxidants. Sautéing and roasting also maintain good nutrient levels. Boiling causes the most nutrient loss as vitamins leach into cooking water.

Potential Side Effects and Considerations

While onions are beneficial for most people, some individuals should exercise caution.

Digestive Discomfort

Onions contain FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols)—carbohydrates that some people cannot properly digest. This can cause:

• Bloating and gas
• Abdominal cramping
• Diarrhea
• General digestive upset

People with irritable bowel syndrome (IBS) or FODMAP sensitivity may need to limit or avoid onions. If considering a low-FODMAP diet, consult a registered dietitian to ensure nutritional adequacy.

Onion Intolerance and Allergy

True onion allergies are uncommon, but intolerance to raw onions is relatively frequent. Symptoms may include:

• Skin reactions (hives, itching, redness)
• Digestive symptoms (heartburn, nausea, upset stomach)
• Oral allergy syndrome (tingling or swelling in the mouth)

Some individuals react to touching onions even without consuming them. If you suspect an onion allergy, consult an allergist for proper testing.

Eye and Nasal Irritation

When onions are cut, they release syn-propanethial-S-oxide, a volatile sulfur compound that causes:

• Tearing and eye irritation
• Temporary burning sensation
• Nasal irritation

To minimize irritation, try chilling onions before cutting, using a sharp knife, cutting under running water, or leaving the root end intact until last.

Breath and Body Odor

The sulfur compounds in onions can cause temporary bad breath and, when consumed in large quantities, may affect body odor. These effects are temporary and can be minimized by consuming fresh herbs like parsley or mint.

Medication Interactions

Onions may interact with certain medications, particularly blood thinners, as they contain compounds with mild anticoagulant properties. If you take medications regularly, discuss your onion consumption with your healthcare provider.

Safety for Pets

Onions are toxic to many animals including dogs, cats, horses, and birds. The sulfur compounds can damage red blood cells in animals, causing hemolytic anemia. Keep onions and onion-containing foods away from pets.

How to Incorporate More Onions Into Your Diet

Here are practical ways to increase onion consumption:

Raw Applications

• Add thin slices to salads and sandwiches
• Include diced red onions in salsas and guacamole
• Make pickled onions for burgers and tacos
• Use as a garnish for soups and grain bowls

Cooked Preparations

• Caramelize yellow onions for deep, sweet flavor
• Roast onions with other vegetables
• Add to stir-fries, soups, and stews
• Grill onion slices as a side dish
• Blend into sauces and dips

Storage Tips

Proper storage extends onion shelf life:

• Store whole onions in a cool, dry, dark place with good air circulation
• Avoid storing with potatoes, which release moisture and gases
• Keep cut onions in airtight containers in the refrigerator for up to 7 days
• Red onions generally have shorter shelf life than yellow or white varieties

Frequently Asked Questions About Onion Nutrition

Which onion variety is healthiest?

Red onions generally contain the highest levels of antioxidants due to their anthocyanin content, followed by yellow onions with high quercetin levels. However, all onion varieties offer significant health benefits, and the best choice depends on your culinary needs and taste preferences.

Do onions lose nutrients when cooked?

Cooking reduces some nutrients like vitamin C but increases the bioavailability of antioxidants like quercetin. Baking and grilling preserve nutrients better than boiling. Both raw and cooked onions offer health benefits.

How many onions should you eat daily?

There’s no specific requirement, but studies showing health benefits often use 50-100 grams (about half a medium onion) daily. Include onions as part of a varied diet rich in different vegetables.

Are onions good for weight loss?

Onions are low in calories (38-42 per 100g) and contain fiber, making them a weight-loss-friendly food. However, they should be part of an overall calorie-controlled, nutrient-dense diet rather than considered a specific weight-loss food.

Can diabetics eat onions?

Yes, research suggests onions may actually help regulate blood sugar levels. However, individuals with diabetes should monitor their response and consult their healthcare provider about dietary changes.

The Bottom Line

Onions are nutritional powerhouses that deserve a regular place in your diet. Whether you choose red, yellow, or white varieties, you’ll benefit from their impressive array of vitamins, minerals, antioxidants, and beneficial plant compounds.

With only 38-42 calories per 100 grams, onions provide significant nutrition with minimal caloric cost. They offer potential benefits for blood sugar regulation, bone health, heart health, and may help reduce the risk of certain chronic diseases.

While some people may experience digestive discomfort or intolerance, most individuals can safely enjoy onions in various forms. Both raw and cooked onions provide health benefits, so choose preparation methods that suit your preferences and digestive tolerance.

By incorporating different onion varieties into your meals, you’ll add flavor, nutrition, and potential health benefits to your daily diet. As with all foods, onions are most beneficial when consumed as part of a balanced, varied diet rich in fruits, vegetables, whole grains, and lean proteins.

Sources:

• USDA FoodData Central – National Nutrient Database
• PubMed Central – National Institutes of Health
• World Health Organization – Nutrition Resources
• NIH Office of Dietary Supplements
• ScienceDirect – Peer-Reviewed Research