Onion Glycemic Index
Low GI · The honest verdict
Gentle on blood sugar
Glycemic index
10
per source
Glycemic load
1
Low GL
This food's glycemic index is 10, which is Low GI.
Onions have one of the lowest glycemic indices of any vegetable, and their prebiotic fiber (fructooligosaccharides) may support gut health and slow carbohydrate absorption. A typical cooking portion has a negligible effect on blood sugar. This is general nutrition information, not medical advice; people with diabetes should consult their care team.
GI numbers vary by source, ripeness, and how a food is prepared. This is general nutrition information — not medical advice. If you manage diabetes, confirm specifics with your care team.
Key facts
Onions contain fructooligosaccharides — prebiotic fibers that resist digestion, feeding gut bacteria and contributing to their very low glycemic index.
The University of Sydney GI Database lists raw onions at a glycemic index of approximately 10 — one of the lowest of any vegetable tested.
Onions are a good source of quercetin, a flavonoid antioxidant that has been studied for potential benefits in metabolic health.
What's actually inside
Per 100 g, with your typical serving noted as 1/2 cup chopped (80 g), raw. The carb family is what moves blood sugar — fiber is the number that softens the spike.
Total carbs
7.5g
Net carbs
6g
total carbs minus fiber
Fiber
1.5g
slows the glucose rise
- Sugars
- 3.4g
- Protein
- 0.7g
- Calories
- 32kcal
Notable nutrients
- Vitamin C7 mg
- Vitamin B60.1 mg
- Folate15 mcg
- Potassium117 mg
- Quercetin (flavonoid)~19 mg
Is it a smart choice for blood sugar?
GI is only half the story — portion (glycemic load) and what you eat it with decide the real-world effect. Here's the honest read.
The verdict
Blood-sugar friendly — low GI and rich in prebiotic fiber
Onions have one of the lowest glycemic indices of any vegetable, and their prebiotic fiber (fructooligosaccharides) may support gut health and slow carbohydrate absorption. A typical cooking portion has a negligible effect on blood sugar. This is general nutrition information, not medical advice; people with diabetes should consult their care team.
Portion guidance
A half-cup to one cup of raw or cooked onion — a realistic culinary portion — contains 6–12 grams of total carbs but a very low glycemic load. Caramelized onions concentrate sugars and increase volume eaten, so portions in that form are worth noting, though they remain a lower-GI choice overall.
This is general nutrition information, not personal medical advice. Blood sugar responses are individual — if you have diabetes or prediabetes, your care team can tell you how this fits your plan.
How to keep the spike small
The same food can land differently depending on how it's cooked and what it's eaten with. Use these levers to your advantage.
Eating raw
Lowers the spikeRaw onion retains its pungent sulfur compounds and full fiber content, keeping digestion slow and the glucose response minimal.
Caramelizing
Raises GILong, slow cooking breaks down fructooligosaccharides into simpler sugars and concentrates carbohydrates as water evaporates — caramelized onions are sweeter and have a somewhat higher glycemic impact per gram than raw. Still low-GI in reasonable amounts.
Light sauteing or roasting
Little effectBrief cooking softens texture without significantly altering the carbohydrate or fiber structure — the glycemic impact remains very close to raw onion.
Pairing tip
Onions are typically used as a flavor base rather than a standalone serving, so their glycemic contribution to a dish is usually small. Add them raw to salads with olive oil and lemon, or sauté lightly with lean proteins and non-starchy vegetables for a well-rounded low-GI plate.
Why GI numbers vary
The glycemic index of onions is consistently reported as very low across major GI databases — the University of Sydney database lists raw onions at around 10, and other sources confirm values in the single digits to low teens. The slightly sweet flavor comes from fructose and fructooligosaccharides rather than glucose-spiking starches, which explains why the GI is so low despite the presence of natural sugars.
Not medical advice. This page is general nutrition information about Onion. It isn't a diagnosis or a treatment plan. If you have diabetes, prediabetes, or another condition affecting blood sugar, confirm any dietary decisions with your doctor or care team.
❓Frequently Asked Questions
Onions have a glycemic index of approximately 10, one of the lowest of any vegetable. Despite their mild sweetness (from fructose and fructooligosaccharides), they raise blood sugar very slowly. The glycemic load for a typical half-cup serving is around 1 — meaning the absolute effect on blood glucose is minimal. Different onion types (white, yellow, red) are all similarly low-GI.
Generally, yes. Onions are a low-GI, prebiotic-rich vegetable with a very low glycemic load per serving. Their quercetin content is also an active area of nutrition research for metabolic health. Most diabetes nutrition guidance includes non-starchy vegetables like onions freely. Heavy caramelization concentrates sugars, so very large portions of caramelized onions are worth moderating — check with your care team for personalized advice.
Very minimally. A half-cup of raw or lightly cooked onion contributes about 6 grams of net carbs and a glycemic load of around 1 — too small to cause a notable blood-sugar rise in most people. Caramelized onions in large quantities have a slightly higher impact because sugars concentrate during cooking, but onions in typical culinary amounts remain blood-sugar friendly.
Both are low-GI options, but raw onion is marginally better from a strictly glycemic standpoint — it retains all its fiber and has not had sugars concentrated by heat. That said, the difference in a typical serving is small. Lightly sauteed onion is still an excellent blood-sugar-friendly choice. Heavy caramelization is the form worth moderating if blood sugar is a priority.
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Reviewed by
Curex Editorial TeamReviewed for accuracy
Last reviewed July 2026