Standard tomato soup is not particularly low carb. A typical can of condensed tomato soup prepared with water contains roughly 20 grams of total carbohydrates per serving, with most of those carbs coming from the natural sugars in tomatoes plus added sugar and thickeners. That said, the carb count varies dramatically depending on whether you’re eating canned, homemade, or a specialty keto-friendly version, and there are easy ways to bring the number down significantly.
Carbs in Canned Tomato Soup
Most commercial tomato soups add sugar, flour, or starch to improve flavor and texture. A full can of standard condensed tomato soup (prepared with water) delivers only about 1.2 grams of fiber, meaning nearly all the carbohydrates hit your bloodstream as sugar. For someone following a strict low-carb or keto diet aiming for 20 to 50 grams of carbs per day, a single bowl can eat up a large chunk of that allowance.
Creamy versions are often worse. Adding milk to condensed soup instead of water tacks on another 6 grams of carbs per cup from the lactose alone. And many “creamy tomato” varieties on store shelves include additional starch or sugar in their ingredient lists, pushing a serving well past 25 grams.
Why Tomatoes Themselves Aren’t the Problem
A medium raw tomato contains just 4.8 grams of carbohydrates and 1.5 grams of fiber, leaving only about 3.3 grams of net carbs. Tomatoes are, on their own, a perfectly reasonable low-carb vegetable. The issue is everything else that goes into a pot of soup: sugar, flour-based thickeners, and high-carb dairy. When you make tomato soup from scratch using whole tomatoes and skip those additions, the carb count drops considerably compared to what comes out of a can.
Tomato soup made with broth as its base (rather than cream or milk) has a glycemic index of about 40, which qualifies as low GI. Its glycemic load per 100 grams is only 2, meaning it causes a slow, gradual rise in blood sugar rather than a spike. That’s relevant if you’re watching carbs for blood sugar management rather than strict ketosis.
Keto-Friendly Brands
A few brands now sell tomato soup specifically marketed to low-carb and keto dieters. Progresso’s Keto Friendly Creamy Tomato Soup, for example, lists 17 grams of total carbohydrates per can but includes 7 grams of fiber, bringing the net carb count to 10 grams for the entire can. It achieves this partly by using 49 grams of fat per can (from cream and oils) to replace the bulk that would normally come from starch and sugar.
Ten net carbs for a full can is workable on a moderate low-carb plan, though it’s still half a day’s allowance on strict keto. Read labels carefully, because “keto-friendly” on packaging doesn’t follow any regulated standard. Some products use that label loosely.
Making Low-Carb Tomato Soup at Home
Homemade versions give you the most control. Start with whole or canned tomatoes (no sugar added), chicken or vegetable broth, garlic, onion, and seasonings. The base of a simple homemade tomato soup built from about four medium tomatoes and a cup of broth can come in under 15 grams of net carbs for the entire pot, which stretches across three or four servings.
Choosing the Right Cream
If you want a creamy texture, heavy cream is the better choice over milk. A full cup of heavy cream contains roughly 6.6 to 6.9 grams of carbohydrates, which is comparable to a cup of whole milk. The difference is that you need far less heavy cream to get the same richness. Two or three tablespoons swirled into a pot of soup adds under 1.5 grams of carbs total while delivering a velvety consistency that milk can’t match without adding flour.
Thickening Without Flour or Cornstarch
Traditional tomato soup recipes call for flour or cornstarch as thickeners, both of which add carbs quickly. Several low-carb alternatives work well. Konjac powder (also called glucomannan) is a high-fiber root extract that thickens soup effectively and adds virtually no digestible carbohydrates. You only need a small amount, roughly a quarter teaspoon per cup of liquid. Guar gum works similarly and is widely available in grocery stores. For a more familiar option, simply blending the cooked soup in a blender or with an immersion blender creates a thick, smooth texture without any thickener at all. The tomato pulp and onion break down into a naturally creamy consistency.
How Different Versions Compare
- Standard canned (1 cup, prepared with water): roughly 20g total carbs, 1g fiber, 19g net carbs
- Canned prepared with milk (1 cup): roughly 26g total carbs, 22+ net carbs
- Keto brand (full can): 17g total carbs, 7g fiber, 10g net carbs
- Homemade broth-based (1 cup): roughly 8 to 12g total carbs, 6 to 9g net carbs depending on recipe
- Homemade with heavy cream, no thickener (1 cup): roughly 8 to 13g total carbs, 6 to 10g net carbs
The Bottom Line on Carbs and Tomato Soup
Standard canned tomato soup is a moderate-carb food that doesn’t fit easily into strict low-carb eating. But the carbs in tomato soup come mostly from added ingredients, not the tomatoes themselves. A homemade batch using whole tomatoes, broth, heavy cream, and no flour or sugar can realistically land between 6 and 10 net carbs per serving, which is manageable on most low-carb plans. If you’re buying off the shelf, check for added sugars in the ingredient list and look for products that list fiber content high enough to bring net carbs into single digits per serving.