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Onion

Vegetable

Onion

A low-calorie, nutrient-dense root vegetable known for its pungent flavor and high antioxidant content.

Onions are pungent, layered root vegetables widely used as a flavor base in cooking. They are low in calories and rich in antioxidants and prebiotic fiber.

low-calorie flavor-enhancing vegetable

Typical serving · 110g

Common varieties · yellow onion, red onion, white onion, sweet onion, shallot +1 more

85health

Overall context score across nutrition, safety, and diet fit

At a glance

Quick facts

Simple indicators based on nutrition, processing, and diet fit.

Low calorieLow carbLow glycemicWeight lossDiabetes-friendlyGut health

The story

What makes it unique

Onions are low-energy, high-water vegetables containing fructans (prebiotic fiber) and the antioxidant quercetin. They digest slowly due to fiber content, providing moderate satiety with minimal caloric load. As a raw whole food, they retain their full phytonutrient profile without processing degradation.

Varieties: yellow onion · red onion · white onion · sweet onion · shallot · scallion

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Per 100g

Nutrition breakdown

Macro balance and key metrics at a glance.

Energy

40kcal

Density 0.40 kcal/g

Protein

1.1g

Carbs

9.3g

Fat

0.1g

Fiber

1.7g

Sugar

4.2 g

Sodium

4 mg

Potassium

146 mg

Glycemic index

15

Glycemic load

1

Water content

89%

Standout compounds

Nutrient highlights

  • Quercetin

    high

    Potent anti-inflammatory and antioxidant properties

  • Fructans

    high

    Prebiotic fiber that feeds beneficial gut bacteria

  • Vitamin C

    moderate

    Supports immune function and collagen synthesis

  • Folate

    moderate

    Essential for cell division and DNA synthesis

Wellness map

Health scores & processing

Weight loss
90
Satiety
65
Blood sugar
95
Gut health
75
Heart health
80
Fitness
50
Processing
100

NOVA processing scale

1
Min
2
3
4
Ultra

minimally processed · Whole food

Raw whole onions are unprocessed agricultural products.

Diet compatibility

  • Weight loss
  • Muscle gain
  • Diabetes
  • Gut health
  • Low carb
  • High protein
  • Heart health

Relative standing

Food rankings

Qualitative ranks compared to similar whole foods.

  • Satietygood
  • Blood sugarexcellent
  • Nutrient densitygood
  • Fitness fuelmoderate
  • Processing qualityexcellent

Eat with confidence

Food safety profile

Onions are generally very safe. Removing the outer papery skin eliminates most surface pesticide residue and soil contamination. Cooking eliminates common microbial risks.

95safety

Evidence confidence 90%

  • Pesticideslow
  • Antibioticslow
  • Heavy metalslow
  • Contaminationlow

Watch for

  • soilborne bacteria

Safer choices

Organic onions if concerned about systemic pesticide uptake, though conventional is low risk.

Prep tips

Rinse under running water and peel the outer skin before consuming raw or cooked.

Minimal; outer layers provide protection from pesticide exposure.

Deep dive

Health analysis

How this food may fit different goals and preparation choices.

  1. Weight loss

    Extremely low energy density allows for high volume eating with minimal calories, making it an excellent weight loss food.

  2. Blood sugar

    Very low glycemic index and load. The fiber content slows carbohydrate absorption, preventing blood sugar spikes.

  3. Fitness & energy

    Not a primary fuel source due to low calories and carbs, but useful for flavoring meals without adding macros.

  4. Gut health

    Rich in inulin and fructo-oligosaccharides that promote beneficial gut bacteria, though high FODMAP content can cause digestive distress in sensitive individuals.

  5. Processing quality

    Whole raw onions are completely unprocessed, retaining maximum nutrient density and antioxidant capacity.

  6. Food safety

    Very low risk. The outer skin protects the edible layers from most pesticides and contaminants.

  7. Common mistakes

    Overcooking onions in large amounts of oil or butter drastically increases the calorie density of the final dish.

  8. Best preparation

    Raw in salads for maximum quercetin retention, or lightly sautéed in water or minimal oil to preserve nutrients while softening pungency.

Practical guide

Best use cases

When and how this food fits real eating patterns.

  • Flavor base for low-calorie cooking

    Sautéing onions with garlic and spices creates a rich flavor foundation without relying on heavy sauces.

  • High-volume salad addition

    Adding raw diced onions to salads increases flavor and food volume with negligible calories.

  • Prebiotic gut health boost

    Consuming raw onions feeds beneficial gut bacteria, supporting microbiome diversity.

Balance sheet

Pros & cons

Upsides

  • Very low in calories and energy density
  • Rich in the antioxidant quercetin
  • Excellent source of prebiotic fiber for gut health
  • Minimal impact on blood sugar levels
  • Adds intense flavor to dishes without fat or sodium

Trade-offs

  • High in FODMAPs, triggering IBS symptoms in sensitive individuals
  • Can cause bad breath and body odor
  • Pungency can be overwhelming when raw
  • Digestive discomfort like gas and bloating is common

Fit check

Who is it for?

Great match

  • low-calorie flavor enhancement
  • high-volume eating
  • blood sugar management
  • prebiotic gut support

Consider alternatives

  • low-FODMAP diets
  • people with severe IBS
  • high-protein meal plans

Side by side

How it compares

Open the full head-to-head analysis for nutrition, safety, and practical tradeoffs.

  • Onion

    This food

    Onion

    VS90% alike
    Garlic

    Compare with

    Garlic

    Garlic offers more micronutrients per gram but is eaten in smaller amounts; onions provide better volume and satiety for weight loss.

    Garlic provides concentrated flavor and micronutrients, while onions offer lower calorie density and better meal volume for weight loss.

    Onion vs Garlic
  • Onion

    This food

    Onion

    VS85% alike
    Shallot

    Compare with

    Shallot

    Shallots are sweeter and denser in calories; onions are lower in calories and better for strict weight loss.

    Shallots offer a milder, sweeter flavor, but onions are lower in calories and carbs, making them better for weight loss and blood sugar control.

    Onion vs Shallot
  • Onion

    This food

    Onion

    VS80% alike
    Leek

    Compare with

    Leek

    Leeks are milder and have slightly more fiber, but onions are lower in calories and carbs.

    Leeks provide a subtler flavor and slightly more fiber, while onions are lower in calories and more versatile for everyday cooking.

    Onion vs Leek
  • Onion

    This food

    Onion

    VS80% alike
    Scallion

    Compare with

    Scallion

    Scallions are lower in carbs and calories per 100g, making them slightly better for strict low-carb diets, but onions offer more volume.

    Scallions are lower in carbs and calories per gram, but onions provide more satiety and a stronger flavor base for cooked dishes.

    Onion vs Scallion
  • Onion

    This food

    Onion

    VS60% alike
    Bell Pepper

    Compare with

    Bell Pepper

    Bell peppers provide vastly more vitamin C, while onions offer stronger prebiotic benefits and a lower glycemic impact.

    Bell peppers are sweeter and higher in vitamin C, while onions are lower in sugar and better for gut health due to prebiotic fiber.

    Onion vs Bell Pepper
  • Onion

    This food

    Onion

    VS55% alike
    Carrot

    Compare with

    Carrot

    Carrots are higher in sugar and vitamin A, while onions are lower in carbs and better for blood sugar control.

    Carrots provide more vitamin A and natural sweetness, but onions are significantly lower in carbs and sugar for blood sugar management.

    Onion vs Carrot
  • Onion

    This food

    Onion

    VS50% alike
    Celery

    Compare with

    Celery

    Celery is lower in calories and carbs, but onions provide significantly more flavor and antioxidant value.

    Celery is lower in calories, but onions deliver much stronger flavor and higher levels of beneficial antioxidants like quercetin.

    Onion vs Celery
  • Onion

    This food

    Onion

    VS50% alike
    Tomato

    Compare with

    Tomato

    Tomatoes are richer in potassium and vitamin C, while onions are lower in sugar and higher in prebiotic fiber.

    Tomatoes offer more vitamin C and potassium, while onions provide fewer sugars and more prebiotic fiber for gut health.

    Onion vs Tomato
  • Onion

    This food

    Onion

    VS45% alike
    Turnip

    Compare with

    Turnip

    Turnips offer more vitamin C and potassium, but onions provide more flavor and a lower glycemic load.

    Turnips are higher in vitamin C, but onions are lower in calories and carbs, making them a better choice for weight loss and blood sugar control.

    Onion vs Turnip
  • Onion

    This food

    Onion

    VS45% alike
    Radish

    Compare with

    Radish

    Radishes are lower in calories and carbs, but onions provide a much stronger flavor base and more prebiotic fiber.

    Radishes are lower in calories and great for raw snacking, while onions offer more prebiotic fiber and a much stronger flavor impact in cooked meals.

    Onion vs Radish

Common questions

FAQ

Answers aligned with how people search for this food.

  • Are onions good for weight loss?

    Yes, onions are very low in calories and high in water and fiber, which helps increase meal volume and satiety without excess calories.

  • Do onions raise blood sugar?

    No, onions have a very low glycemic index and glycemic load, meaning they have minimal impact on blood sugar levels.

  • Are onions keto-friendly?

    Yes, while they contain carbs, the net carbs are low enough to fit into a ketogenic diet when consumed in typical serving sizes.

  • Are onions good for gut health?

    Onions contain prebiotic fiber (fructans) that feeds beneficial gut bacteria, but they are high in FODMAPs and can cause bloating in people with IBS.

  • What is the healthiest way to eat onions?

    Eating onions raw maximizes their antioxidant and vitamin C content, but lightly cooking them makes them easier to digest for some people.

  • Which onion is the healthiest?

    Red onions generally contain the highest levels of antioxidants, particularly quercetin and anthocyanins, compared to white or yellow varieties.

  • Can diabetics eat onions?

    Yes, onions are safe and beneficial for diabetics due to their low glycemic index and fiber content that helps regulate blood sugar.

  • Why do onions make you cry?

    Cutting onions breaks their cells, releasing enzymes that create syn-propanethial-S-oxide, a gas that irritates the eyes and triggers tears.

Transparency

Data confidence

Estimated confidence for nutrition data, interpretation, safety notes, and comparisons.

95

Nutrition data

90

Health analysis

95

Food safety

90

Comparisons