Tomato vs Onion: Nutrition Comparison
Which is healthier? Compare calories, protein, carbs, and more
Complete side-by-side nutrition comparison per 100g serving | Updated 2026
Which is Healthier?
Onion is generally healthier
Onion comes out ahead in this comparison, winning in 3 out of 5 key nutritional categories. It has more protein (1.1g vs 0.9g), more fiber (1.7g vs 1.2g), less sodium (4mg vs 5mg)making it the better choice for most health goals.
Quick Summary
Fewer Calories
Tomato
18 kcal
More Protein
Onion
1.1g
More Fiber
Onion
1.7g
Less Sugar
Tomato
2.6g
Visual Comparison
Side-by-Side Nutrition Table
Serving Size Comparison
All values above are per 100g. Here's how they compare in common serving sizes:
Tomato
Onion
Diet Compatibility
Tomato
Onion
When to Choose Tomato
- ✓Lower in calories (18 vs 40)
- ✓Lower in carbs (4g vs 9g)
- ✓Less sugar (2.6g vs 4.2g)
Common Uses
When to Choose Onion
- ✓Higher in protein (1.1g vs 0.9g)
- ✓More fiber (1.7g vs 1.2g)
- ✓Lower sodium (4mg vs 5mg)
Common Uses
Tomato vs Onion: Nutritional Analysis
Onion is more calorie-dense at 40 calories per 100g compared to 18 for Tomato, a difference of 22 calories. On the protein front, Onion delivers more with 1.1g per 100g versus 0.9g, which matters for muscle maintenance, satiety, and overall metabolic health. These differences become meaningful when you consider how each food fits into your daily dietary pattern rather than looking at any single nutrient in isolation.
Macronutrient Breakdown
The macronutrient profiles of Tomato and Onion tell different nutritional stories. Tomato provides 4g of carbohydrates, 0.2g of fat, and 1.2g of fiber per 100g, while Onion contains 9g carbs, 0.1g fat, and 1.7g fiber. The higher fiber content in Onion supports digestive health, helps regulate blood sugar after meals, and contributes to longer-lasting satiety. Sugar content also differs: Tomato contains 2.6g while Onion has 4.2g per 100g. Lower sugar options are generally preferable for blood sugar management and dental health.
Key Takeaways
- For weight management: Tomato is the lower-calorie choice at 18 cal/100g, making it more suitable for calorie-controlled diets.
- For muscle building: Onion provides more protein (1.1g/100g), supporting muscle repair and growth.
- For sustained energy: Onion offers more fiber (1.7g/100g), which slows digestion and provides steadier energy release.
- Overall: Neither food is universally "better" than the other. The right choice depends on your specific nutritional goals, meal context, and dietary preferences. Both can play a role in a balanced diet.
Frequently Asked Questions
Which has more calories, Tomato or Onion?
Onion has more calories with 40 kcal per 100g, compared to Tomato with 18 kcal. That's a difference of 22 calories per 100g serving.
Is Tomato healthier than Onion?
Based on our nutritional analysis, Onion is generally the healthier choice, winning in 3 out of 5 key nutritional categories. Onion has 40 calories, 1.1g protein, and 1.7g fiber per 100g. However, the best choice depends on your specific dietary goals.
What is the protein difference between Tomato and Onion?
Onion has more protein with 1.1g per 100g, compared to Tomato with 0.9g. Onion provides 0.2g more protein per 100g serving.
Which is better for weight loss, Tomato or Onion?
For weight loss, Tomato is the better choice with only 18 calories per 100g compared to 40 calories in Onion. Onion also offers 1.7g of fiber per 100g, which helps you feel fuller longer.
Does Tomato or Onion have fewer carbs?
Tomato has fewer carbs with 4g per 100g, compared to Onion with 9g. If you're following a low-carb diet, Tomato is the better option with 5.0g fewer carbohydrates.
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About Our Data
All nutrition data in this comparison is sourced from the USDA FoodData Central, the official food composition database maintained by the U.S. Department of Agriculture. Values are based on 100g servings for accurate comparison.
Health Disclaimer: This comparison is for informational purposes only and is not intended as medical or dietary advice. Nutritional needs vary by individual. The best food choice depends on your personal health goals, dietary requirements, and preferences. Consult a healthcare provider or registered dietitian for personalized nutrition guidance.