One cup of cooked black beans contains about 41 grams of total carbohydrates. That number drops to roughly 26 grams of net carbs once you subtract the 15 grams of dietary fiber. This makes black beans a moderate-carb food that delivers a lot of nutritional value alongside those carbohydrates, including over 15 grams of protein per cup.
Full Carb Breakdown Per Serving
Here’s what one cup (about 172 grams) of boiled black beans looks like nutritionally:
- Total carbohydrates: 40.8 g
- Dietary fiber: 15 g
- Net carbs: ~26 g
- Protein: 15.2 g
- Fat: 0.9 g
- Calories: 227
A half-cup serving, which is the standard portion listed on most labels, comes in at about 20 grams of total carbs and 12 grams of net carbs. That’s the number most people will encounter when checking a can.
Why the Fiber Matters
Nearly 37% of the carbohydrates in black beans come from fiber, which your body doesn’t digest or convert into blood sugar. That’s why net carbs (total carbs minus fiber) gives a more useful picture of how black beans actually affect your body. Of that 15 grams of fiber per cup, roughly 5.6 grams is soluble fiber, the type that slows digestion and helps regulate cholesterol and blood sugar. The remaining 9 to 10 grams is insoluble fiber, which supports gut motility.
Black beans also contain resistant starch, a type of carbohydrate that behaves more like fiber than like sugar. Fully cooked beans contain about 4 to 5% of their dry weight as resistant starch. If you cook black beans and then refrigerate them for up to 24 hours, that rises to 5 to 6% as some of the starch molecules recrystallize. This means leftover black beans or cold bean salads may have a slightly smaller blood sugar impact than freshly cooked ones.
How Black Beans Affect Blood Sugar
Black beans have a glycemic index of 30, which is considered low. For reference, anything under 55 is classified as low-GI, and pure glucose sits at 100. The combination of fiber, resistant starch, and protein in black beans slows the rate at which glucose enters your bloodstream, preventing the sharp spikes you’d get from refined carbs with the same total carbohydrate count. This is one reason beans are consistently recommended for people managing blood sugar levels.
Canned vs. Dried: Any Difference?
The carbohydrate content is essentially the same whether you cook black beans from dried or open a can. The major difference is sodium. Canned black beans can contain up to 100 times more sodium than home-cooked beans. Draining and rinsing canned beans removes roughly half of that added sodium, though you’ll also rinse away small amounts of water-soluble nutrients in the process. If you’re only tracking carbs, canned and cooked from dry are interchangeable.
Black Beans vs. Other Beans
Black beans sit on the lower end of the carb spectrum compared to other popular legumes. Pinto beans, for instance, contain about 44.8 grams of total carbs per cup, roughly 4 grams more than black beans, with a similar fiber count of 15.4 grams. The calorie difference is modest too: 227 for black beans versus 245 for pinto. Protein is nearly identical between the two at around 15 grams per cup. If you’re choosing between common beans and carbs are a factor, black beans give you a slight edge.
Black Beans on a Low-Carb or Keto Diet
With 26 grams of net carbs per cup, black beans are a tough fit for strict keto diets that cap daily net carbs at 20 to 50 grams. A full cup could use up your entire carb budget for the day. A half-cup serving is more manageable at 12 grams of net carbs, and that’s the portion size typically recommended for anyone trying to include beans on a ketogenic plan. At that amount, you still get about 7.5 grams of protein and a meaningful dose of fiber without blowing past your carb limit.
For moderate low-carb diets (under 100 to 150 grams of carbs daily), black beans fit comfortably. Their low glycemic index and high fiber content mean they behave very differently in your body than 41 grams of carbs from bread or pasta would. Context matters more than the raw number on the label.