Is French onion soup ok on a keto diet? The ultimate guide

November 23, 2025 •

2 min read

A traditional bowl of French onion soup is unfortunately not keto-friendly due to its high carb ingredients. However, with clever substitutions and careful preparation, it's absolutely possible to enjoy a rich, cheesy, and deeply satisfying version of French onion soup on a keto diet.

Quick Summary

This article explores why traditional French onion soup is not suitable for a keto diet and provides an in-depth guide to making a delicious, low-carb version. It covers key ingredient swaps, a simplified recipe, and addresses common questions for staying in ketosis.

Key Points

Traditional is not keto: Classic French onion soup contains high-carb ingredients like a large amount of onions, flour, and baguette croutons.
Keto is possible with modification: You can create a keto-friendly version by reducing the onions and eliminating high-carb bread and thickeners.
Caramelize onions wisely: Cook a smaller amount of onions slowly in butter or oil without added sugar to concentrate their natural sweetness.
Choose the right broth: Use a high-quality beef bone broth for a flavorful, carb-free liquid base.
Use low-carb toppings: Substitute the traditional baguette with toasted keto bread, a "chaffle," or just extra cheese.
Cheese is keto-approved: Cheeses like Gruyère and Swiss are perfectly fine for a keto diet and add essential fats and flavor.

Traditional French Onion Soup and the Keto Problem

Traditional French onion soup features caramelized onions, savory broth, and a bread and melted cheese topping. While the broth and cheese fit keto, other elements are carb-heavy. The main carb sources are the onions, which sweeten significantly when caramelized, the high-carb baguette crouton, and often flour used for thickening. White wine used to deglaze can also add carbs.

Making French Onion Soup Keto-Friendly

Adjusting a few key components allows for a delicious keto version.

Keto-Friendly Ingredients and Techniques

Reduced Onions: Limit the quantity of onions used.
Keto Caramelization: Slowly caramelize onions in fat without added sugar. Low-carb sweeteners can be used but aren't essential.
Beef Broth Base: Use a high-quality, carb-free beef bone broth.
Keto Thickener: Xanthan gum can be used sparingly instead of flour.
Low-Carb Topping: Replace the baguette with toasted keto bread, a "chaffle," or just extra cheese.
Proper Cheese: Keto-friendly cheeses like Gruyère or Swiss are suitable.

Keto vs. Traditional French Onion Soup

This table highlights the major differences between a classic French onion soup and a keto-friendly version.


Feature	Traditional French Onion Soup	Keto French Onion Soup
Onions	Large quantity, often with added sugar for caramelization	Smaller quantity, caramelized slowly with no added sugar
Thickener	All-purpose flour	Xanthan gum (optional) or no thickener
Broth	Standard beef or onion stock	High-quality beef bone broth
Topping	French baguette slice with melted cheese	Toasted keto bread, chaffle, or no bread
Cheese	Gruyère, Swiss, or Emmental	Gruyère, Swiss, or a similarly low-carb cheese
Net Carbs	High (over 20g per serving)	Low (typically under 10g per serving)

Simple Keto French Onion Soup Recipe

This recipe offers a low-carb alternative.

Ingredients

3 Tbsp unsalted butter
2 large yellow onions, thinly sliced
2 minced garlic cloves
1 tsp fresh thyme leaves
4 cups beef bone broth
1/4 cup dry white wine or sherry (optional)
4 slices keto-friendly bread
1 cup shredded Gruyère or Swiss cheese
Salt and black pepper to taste

Instructions

Melt butter, add onions and salt, and cook on low heat for 30-40 minutes until caramelized.
Add garlic and thyme for one minute.
Deglaze with wine if using, then reduce.
Add beef broth, simmer for 20 minutes, and season.
Toast keto bread separately.
Ladle soup into oven-safe bowls, top with toasted bread and cheese.
Broil for 3-5 minutes until bubbly and golden. Serve immediately.

Conclusion

While traditional French onion soup's high carbs make it non-keto, modifications make it suitable. Reducing onions, using bone broth, and substituting the bread with keto-friendly options or skipping it entirely allows you to enjoy the flavor while staying in ketosis. Portion control is important for ingredients like onions. This comforting dish can fit into a ketogenic diet with a few adjustments.

For more on the ketogenic diet, consult resources like Healthline or the University of California, Davis Health.

Frequently Asked Questions

Traditional French onion soup is not suitable for a keto diet because it typically contains a large number of onions, which are a source of carbohydrates, flour as a thickener, and a high-carb baguette crouton.

Yes, onions can be consumed in moderation on a keto diet. The key is portion control, as their carb count can add up, especially when concentrated through caramelization. Use fewer onions in your keto version to manage carbs.

Gruyère is the classic choice and is perfectly keto-friendly. Swiss cheese is also an excellent substitute. Both melt well and have minimal carbs.

You can use a small amount of xanthan gum, a low-carb thickener, to achieve the desired consistency. A little goes a long way, so start with a small amount and whisk thoroughly to prevent clumping.

Keto-friendly bread is a great substitute. Alternatively, you can use a "chaffle" made from cheese and egg, or simply omit the bread entirely and top with a generous amount of melted cheese.

While caramelizing doesn't add carbs, it concentrates the natural sugars and flavor, meaning you get a more potent dose of carbs in a smaller volume. This is why reducing the total amount of onions used is important for keto.

Yes, beef bone broth is an ideal ingredient for a keto diet. It is low in carbs, high in nutrients, and provides a rich flavor base for soups.