Carbs in Onion: Exact Counts by Variety & Dietary Impact

A medium raw onion (110g) contains approximately 10.3g total carbohydrates, including 1.9g dietary fiber and 4.7g natural sugars. This makes onions a moderate-carb vegetable that fits within most balanced diets when consumed in typical culinary portions.

Understanding the carbohydrate composition of onions helps home cooks and health-conscious eaters make informed decisions about this kitchen staple. While onions add incredible flavor to dishes worldwide, their carb content matters for those managing diabetes, following low-carb diets, or tracking nutritional intake precisely.

Onion Carbohydrate Breakdown by Variety

Not all onions are nutritionally identical. The carbohydrate content varies slightly between common varieties based on water content and natural sugar concentration. The USDA FoodData Central database provides the most reliable measurements for raw onions:

Onion Type	Carbs per 100g	Fiber Content	Sugars	Net Carbs*
Yellow Onion (raw)	9.34g	1.7g	4.24g	7.64g
Red Onion (raw)	9.53g	1.8g	4.41g	7.73g
White Onion (raw)	8.97g	1.6g	4.03g	7.37g
Green Onions (raw)	6.96g	2.6g	2.79g	4.36g
Shallot (raw)	15.94g	3.1g	7.87g	12.84g

*Net carbs = Total carbs minus fiber. Source: USDA FoodData Central

How Cooking Changes Onion Carbohydrates

Many home cooks wonder whether cooking affects onion carb content. The cooking process concentrates carbohydrates as water evaporates, but doesn't significantly alter the total carb count per serving:

• Sautéed onions: 1 cup (160g) contains approximately 14.9g total carbs (more concentrated due to reduced volume)
• Caramelized onions: The natural sugars undergo the Maillard reaction, but total carbohydrate content remains similar to raw (about 9-10g per 100g)
• Roasted onions: Minimal change in carb composition, though some sugars may caramelize on the surface

When tracking carbohydrates for medical or dietary reasons, remember that cooking reduces volume but not total carbohydrate content. A cup of raw chopped onions (160g) contains about 15g carbs, while that same cup of cooked onions represents significantly more raw onion material.

Practical Dietary Considerations

For most people, the carbohydrate content in onions presents no concern. However, specific dietary contexts require attention to onion portions:

Keto and Low-Carb Diets

Onions contain moderate carbohydrates that can challenge strict ketogenic diets (typically limited to 20-50g net carbs daily). Consider these practical approaches:

• Use green onions instead of bulb onions (nearly 40% fewer net carbs)
• Limited to 2-3 tablespoons of finely diced onion per serving when following strict keto
• Substitute with asafoetida (hing) for onion flavor in Indian cuisine with minimal carbs
• Save your carb budget for onions in dishes where flavor impact justifies the carb count

Diabetes Management

While onions contain carbohydrates, they also provide chromium and sulfur compounds that may support blood sugar regulation. The American Diabetes Association considers onions a non-starchy vegetable suitable for diabetes meal plans when consumed in standard culinary portions (typically 1/4 to 1/2 cup per serving).

Understanding Fructans in Onions

Onions contain fructans, a type of carbohydrate that functions as prebiotic fiber. While technically counted in total carbohydrates, fructans provide only partial caloric value as humans lack the enzyme to fully break them down. This explains why some people experience digestive discomfort from onions despite their moderate carb count.

Maximizing Flavor While Managing Carbs

Professional chefs use several techniques to extract maximum onion flavor while minimizing carbohydrate impact:

1. Infusion method: Simmer onion slices in cooking liquid, then remove before serving to capture flavor without the bulk
2. Layering technique: Use small amounts of high-quality onions at multiple cooking stages rather than one large addition
3. Varietal selection: Choose stronger-flavored varieties like red onions where smaller quantities deliver equivalent flavor impact
4. Combination approach: Blend onions with lower-carb aromatics like celery and bell peppers to distribute flavor impact

These professional techniques allow home cooks to maintain rich flavor profiles while managing carbohydrate intake effectively.

Common Misconceptions About Onion Carbs

Several myths persist about onion carbohydrates that deserve clarification:

• Myth: Cooking significantly reduces onion carbs
  Fact: Cooking concentrates carbs as water evaporates but doesn't destroy carbohydrates
• Myth: All onion varieties have identical carb content
  Fact: Shallots contain nearly 70% more carbs than white onions per equivalent weight
• Myth: Onion carbs cause significant blood sugar spikes
  Fact: The glycemic load of a typical onion serving is low due to fiber content and small portion sizes used

How many carbs are in a medium onion?

A medium raw onion (approximately 110g) contains about 10.3g total carbohydrates, including 1.9g dietary fiber and 4.7g natural sugars.

Are onions suitable for a keto diet?

Onions can fit into a keto diet in limited quantities. A standard serving (1-2 tablespoons of diced onion) contains 1-2g net carbs. For strict keto, consider using green onions which have nearly 40% fewer net carbs than bulb onions.

Do cooked onions have more carbs than raw onions?

Cooked onions have more concentrated carbs per volume because water evaporates during cooking, but the total carb content remains similar. A cup of cooked onions represents more raw onion material than a cup of raw chopped onions.

Which onion variety has the lowest carbohydrate content?

Green onions (scallions) have the lowest carbohydrate content among common onion varieties, with approximately 6.96g total carbs per 100g compared to 8.97-9.53g for bulb onions. White onions also have slightly fewer carbs than yellow or red varieties.

How do onions affect blood sugar levels?

Onions have a minimal impact on blood sugar due to their fiber content and typical small serving sizes. The American Diabetes Association classifies onions as a non-starchy vegetable suitable for diabetes meal plans when consumed in standard culinary portions (1/4 to 1/2 cup).