Is Onion keto?
Keto in moderation 4.2 g net carbs per half a medium onion (55 g) — 21% of a 20 g keto day.
Short answer: In moderation. Half a medium onion (55 g): 4.2 g net carbs — 21% of a strict 20 g keto day — with 0.1 g fat and 0.6 g protein.
Log onion in KetoraFree. Weigh it once and Ketora remembers your portion.
Onion is higher in carbs than most vegetables, but it is usually a flavouring rather than the main ingredient. A few slices in a dish costs very little.
How onion fits a keto carb budget
On a 20 g day, one serving uses 21% of your budget, leaving 15.8 g for everything else. Measure portions rather than eyeballing them.
Worked example. 55 g of onion = 5.1 g total carbs − 0.9 g fibre = 4.2 g net carbs, 0.1 g fat, 0.6 g protein and 22 kcal.
Portion is everything here. Weigh it the first few times, and use the keto macro calculator to see how much room your own carb budget leaves.
Nutrition facts
| Nutrient | Per 100 g | Per half a medium onion (55 g) |
|---|---|---|
| Calories | 40 kcal | 22 kcal |
| Fat | 0.1 g | 0.1 g |
| Protein | 1.1 g | 0.6 g |
| Total carbohydrate | 9.3 g | 5.1 g |
| Fibre | 1.7 g | 0.9 g |
| Net carbs | 7.6 g | 4.2 g |
Where the energy comes from:
How to eat onion on keto
- Green onion tops and chives give onion flavour with fewer carbs.
Keto recipes with onion
- Keto Burger Bowl
- Keto Chicken Tikka
- Keto Beef Chili (No Beans)
- Keto Shakshuka
- Keto Zucchini Lasagna
- Crustless Bacon and Spinach Quiche
- Keto Cheeseburger Casserole (Hamburger Casserole)
- Keto Jambalaya with Cauliflower Rice
- Crispy Keto Onion Rings (Oven or Air Fryer)
- Keto Chicken Enchiladas
- Keto Tacos with Cheese Taco Shells
- Keto Broccoli Cheddar Soup
Compared with other vegetables
Onion ranks #21 of 26 vegetables in our database by net carbs per 100 g (lowest first). Most non-starchy vegetables fit easily; roots and tubers are where carbs climb.
| Food | Net carbs / 100 g | Per serving |
|---|---|---|
| Kale | 0.3 g | 0.1 g |
| Lettuce (romaine) | 1.2 g | 1.1 g |
| Spinach | 1.4 g | 0.8 g |
| Celery | 1.4 g | 1.1 g |
| Pickles (dill) | 1.4 g | 0.9 g |
| Asparagus | 1.8 g | 1.7 g |
See all vegetables ranked by net carbs →
Frequently asked questions
How many net carbs are in onion?
Onion has about 7.6 g of net carbs per 100 g (9.3 g total carbohydrate minus 1.7 g fibre), and about 4.2 g per half a medium onion (55 g).
Can you eat onion on keto?
In measured portions. One half a medium onion uses about 21% of a 20 g day, so plan the rest of the day around it.
Values are per 100 g of the raw or stated food, rounded, from USDA FoodData Central. Brands and varieties differ — check the label for packaged products.