A standard cup of tomato soup contains about 18.8 grams of total carbohydrates, with 17.4 grams of net carbs after subtracting fiber. That puts it in a moderate range for most diets, but it can be a significant chunk of your daily allowance if you’re eating low-carb or keto. The exact number varies widely depending on whether you’re eating canned, restaurant, or homemade versions.
Carbs in a Typical Serving
One cup (244 grams) of ready-to-serve tomato soup prepared with water provides roughly 18.8 grams of total carbohydrates and 1.5 grams of fiber, leaving about 17.4 grams of net carbs. Most of those carbs come from the natural sugars in tomatoes, but many commercial brands add extra sugar, flour, or starch as thickeners, which pushes the count higher. Campbell’s condensed tomato soup, for example, clocks in at around 43 grams of carbs per cup when prepared, more than double a basic recipe.
For context, a large raw tomato on its own has only about 7 grams of carbs per 100 grams. The jump in a finished soup comes from concentrating the tomatoes and from whatever gets added during processing. If you’re watching carbs, reading the nutrition label matters more with tomato soup than with most other soups, because the range from brand to brand is enormous.
How It Affects Blood Sugar
Despite the moderate carb count, tomato soup has a glycemic index of 38 and a glycemic load of just 2.7. Both numbers fall into the “low” category, meaning the soup is unlikely to cause a sharp blood sugar spike compared to foods like white bread or rice. The acidity of tomatoes and the water content of the soup both slow digestion, which helps your body absorb the sugars more gradually.
That said, tomato soup is low in protein (under 2 grams per cup) and low in fat unless cream is added. Eating it on its own won’t keep you full for long, and pairing it with a high-carb side like crackers or a grilled cheese sandwich can change the blood sugar picture significantly. Adding a protein source or healthy fat alongside the soup helps balance the meal.
Does Tomato Soup Work on Keto?
Most people following a ketogenic diet aim for 20 to 50 grams of net carbs per day. A single cup of standard tomato soup at 17 grams of net carbs would eat up a third to nearly all of that allowance, making it a tough fit. Canned versions with added sugar are even harder to justify.
Keto-adapted tomato soup recipes solve this by cutting the sugar entirely and replacing traditional thickeners with fats. A typical approach uses cream cheese, heavy cream, or sour cream to create body and richness without the carbs. These homemade versions can bring the count down to around 4 to 6 grams of net carbs per cup while delivering roughly 86 calories. For a dairy-free option, coconut oil and coconut cream work as substitutes. A small amount of a sugar-free sweetener can offset the acidity that tomatoes naturally bring.
What Drives the Carb Count Up
Three ingredients are responsible for most of the carb variation between tomato soups:
- Added sugar: Many commercial brands add sugar or high-fructose corn syrup to balance tomato acidity. This alone can double the carb content compared to a no-sugar recipe.
- Flour and starch: Wheat flour, cornstarch, and modified food starch are common thickeners in canned soups. They contribute carbs without adding much flavor or nutrition.
- Tomato paste concentration: More concentrated tomato paste means more natural sugars per serving. Recipes that use fresh tomatoes or crushed tomatoes tend to be lighter on carbs than those built around paste.
Lower-Carb Ways to Make It
If you enjoy tomato soup but want to keep carbs in check, making it at home gives you the most control. Start with crushed or diced tomatoes instead of paste, use broth as the liquid base, and skip any flour or sugar. Fresh basil (about 2 cups, or 2 tablespoons dried) and a couple of minced garlic cloves add flavor without meaningful carbs.
For creaminess, stir in cream cheese or heavy cream near the end of cooking. Both add fat and body while keeping net carbs low. The fat also slows digestion, which means you’ll stay full longer and see less of a blood sugar response than you would from a water-based version. A cup of this style of soup typically lands around 4 grams of net carbs, making it compatible with even strict low-carb plans.