What is the richest food source of quercetin? The surprising answer

At over 233 mg per 100 grams, the humble caper is by far the richest food source of quercetin, a powerful flavonoid antioxidant. While many fruits and vegetables contain this beneficial compound, capers offer a concentration that far surpasses most other common options.

Quick Summary

Capers are the richest food source of quercetin, a potent antioxidant. Top vegetable sources include red onions and kale, although content is influenced by growing methods and preparation.

Key Points

• Capers are the Richest Source: Raw capers contain the highest concentration of quercetin of any known food, with over 233 mg per 100 grams.

• Onions Are a Top Vegetable Source: Red onions, especially their outer rings, are the highest vegetable source and offer a highly bioavailable form of quercetin.

• Bioavailability Varies by Source: The body's ability to absorb quercetin depends on the food. For instance, quercetin from onions is better absorbed than from tea or apples.

• Cooking Matters: High-heat cooking, especially boiling, can significantly reduce quercetin content in foods. Raw or lightly cooked options preserve more of the flavonoid.

• Eat the Skin: A large portion of quercetin is concentrated in the skin or peels of fruits like apples. Eating whole, unpeeled fruits maximizes intake.

• Pair with Healthy Fats: To further boost absorption, consider consuming quercetin-rich foods alongside healthy fats, such as olive oil in a salad dressing.

What is Quercetin?

Quercetin is a powerful plant pigment, or flavonoid, known for its strong antioxidant and anti-inflammatory properties. Found naturally in a wide array of fruits and vegetables, this compound plays a significant role in helping the body combat free radicals, which are unstable molecules that can cause cellular damage over time. A diet rich in quercetin is associated with numerous potential health benefits, including supporting cardiovascular health, managing inflammation, and boosting immune function. As the human body cannot produce quercetin, it must be obtained through dietary sources.

The Surprising Champion: Capers

When considering the richest food source of quercetin, most people might guess a common berry or leafy green. However, the top spot is held by capers, the edible flower buds of the caper bush. Raw capers, in particular, can contain an exceptionally high concentration of quercetin, reportedly over 233 mg per 100 grams. Even when pickled, capers maintain a very high content, averaging around 173 mg per 100g. These tiny, salty buds, a staple in Mediterranean cuisine, can be easily incorporated into salads, pasta sauces, or as a garnish for seafood and bagels to provide a significant quercetin boost.

Other High-Quercetin Food Sources

While capers lead the pack, several other foods are excellent sources of this valuable flavonoid. Red onions stand out as the vegetable with the highest quercetin content, particularly in the outer layers and closest to the root. Other strong contenders include:

• Herbs and Leafy Greens: Fresh dill (55.15 mg/100g) and coriander leaves (52.90 mg/100g) are potent sources, along with wild arugula and radicchio. Kale is also recognized as a nutritional powerhouse rich in quercetin.
• Berries and Fruits: Dark berries like cranberries (25.0 mg/100g) and blueberries (14.6 mg/100g) are rich in quercetin. Cherries (17.4 mg/100g), apples with the skin on (approx. 4.4 mg/100g), and tomatoes (especially cherry and organic varieties) are also good choices.
• Beverages: Green and black teas are significant contributors to overall flavonoid intake. Red wine, made from red grapes, also contains a notable amount.
• Other Vegetables: Cooked asparagus, shallots, and broccoli are all part of a quercetin-rich diet.

Factors Affecting Quercetin Content and Bioavailability

Simply consuming a food high in quercetin doesn't guarantee maximum absorption. Several factors can influence how much of the flavonoid your body can use:

• Cooking Methods: Heat can degrade quercetin. Studies show that boiling onions is the least effective method for preserving quercetin, leading to a loss of about 30%. Frying and microwaving appear to be less damaging, and eating many sources raw is ideal.
• Food Part: The concentration of quercetin is often highest in the outer parts and skin of fruits and vegetables. For instance, eating an apple with its skin on provides significantly more quercetin than without.
• Cultivation: The way produce is grown can impact its flavonoid content. One study found that organic tomatoes had up to 79% more quercetin than conventionally grown ones.
• Bioavailability: Quercetin is not very water-soluble, which limits its absorption. Research indicates that the form of quercetin found in onions (a glucoside) is better absorbed than the form in apples and tea (a rutinoside). Some evidence suggests pairing quercetin-rich foods with healthy fats can improve absorption.

Comparison of Common Quercetin Sources

Food Source	Approximate Quercetin Content (mg/100g)	Notes on Content and Preparation
Capers (raw)	233.8	Highest concentration; often brined, so check sodium intake.
Dill (fresh)	79.0	A potent herb, best consumed fresh to retain content.
Coriander leaves (raw)	52.9	Rich in the raw form; used widely as an herb.
Fennel leaves	46.8	Significant source, also potent when fresh.
Onions (yellow/red)	45.0	Content highest in outer rings; better absorbed from onions than tea.
Chili pepper	32.6	Adds a spicy kick and a dose of flavonoids.
Spinach	27.2	Another great leafy green option.
Cranberries	25.0	Excellent berry source; also available frozen.
Kale	22.6	A well-known nutritional powerhouse.
Cherry	17.4	Good fruit source with other antioxidants.
Blueberries	14.6	Small but mighty; also rich in other phytochemicals.
Asparagus	14.0	Content may be higher when cooked.
Broccoli	13.7	A classic cruciferous vegetable source.

Incorporating More Quercetin into Your Diet

Increasing your daily quercetin intake doesn't require drastic diet changes, but rather mindful choices about preparation and consumption. Here are some simple strategies:

• Use Capers Often: Add a tablespoon of rinsed capers to salads, pasta, or fish dishes to add a tangy flavor and a significant quercetin boost.
• Eat Your Onions Raw: Add slices of red onion to sandwiches, wraps, and salads. For a milder taste, soak the slices in lemon juice and salt for 10 minutes.
• Prioritize Skins and Peels: When eating fruits like apples, pears, and grapes, consume them with the skin on, as the pigment-rich skin contains a high concentration of flavonoids.
• Enjoy Berries Daily: Add a handful of blueberries, cranberries, or raspberries to your breakfast yogurt, oatmeal, or smoothies. Frozen berries are just as effective and available year-round.
• Switch Your Brew: Replace a cup of coffee with a cup of green or black tea, which can contribute to your daily quercetin intake.
• Massage Your Kale: To make raw kale more palatable in salads, simply massage the leaves with a little olive oil and lemon juice to soften them up.
• Add Fresh Herbs: Incorporate fresh dill, coriander, and oregano into your cooking to sprinkle extra quercetin into your meals.

Conclusion

While many plant-based foods offer a healthy dose of quercetin, capers are the undisputed richest food source. For those looking to maximize their intake of this powerful flavonoid, incorporating capers and other top-tier foods like red onions, dill, and various berries into meals can be highly effective. Understanding the nuances of preparation and bioavailability—such as preferring raw or lightly cooked methods and eating skins—can further enhance the benefits. Ultimately, a varied diet rich in colorful, whole plant foods remains the best approach to ensuring a consistent and diverse supply of beneficial antioxidants like quercetin. For more detailed nutritional information on food sources, the USDA FoodData Central database is an authoritative resource for researchers and health enthusiasts alike.

Frequently Asked Questions

Which food has the highest concentration of quercetin?

Capers have the highest concentration of quercetin, with over 233 mg per 100 grams in their raw form.

Is it better to get quercetin from food or supplements?

Getting quercetin from whole foods is generally recommended, as it provides additional vitamins, minerals, and other phytochemicals that work together synergistically. However, some supplements are specially formulated to increase absorption.

How does cooking affect the quercetin content in food?

Cooking can reduce the quercetin content, with boiling being the least effective method for retention. For example, boiling onions can result in a 30% loss of flavonoids. Eating foods raw or lightly cooked is preferable.

Is quercetin better absorbed from some foods than others?

Yes, studies have shown that the quercetin found in onions is more bioavailable and better absorbed than the quercetin in tea or apples. Absorption is also enhanced when consumed with dietary fat.

What are some other common foods rich in quercetin besides capers?

Besides capers, other excellent sources include red onions, kale, bell peppers, fresh herbs like dill and coriander, berries (cranberries, blueberries), apples (with the skin), and green and black teas.

Does eating an apple with the skin on increase my quercetin intake?

Yes, a significant amount of quercetin in an apple is concentrated in its skin. Eating the apple unpeeled will give you a higher dose of the antioxidant.

Can I increase my quercetin intake by drinking tea?

Yes, both green and black tea are good sources of quercetin. Though the quercetin form in tea is less bioavailable than that in onions, it still contributes to overall intake.

How can I easily add more quercetin to my meals?

Easily add more quercetin by sprinkling capers over salads, using red onions in wraps, snacking on berries, and including fresh herbs like dill or coriander in your recipes.