One cup of cooked black beans contains about 15 grams of protein. That makes them one of the more protein-rich plant foods you can eat, though the quality and usability of that protein depends on how you prepare them and what you eat them with.
Protein Per Serving
A standard one-cup serving of cooked black beans (boiled, no salt) provides 15 grams of protein alongside roughly 218 calories. That works out to about 7% protein by weight once cooked, since beans absorb a lot of water during cooking. For context, you’d need to eat about two cups of black beans to match the protein in a typical chicken breast.
Canned black beans have a similar protein content per cup, though the sodium is significantly higher unless you rinse them. Rinsing canned beans under water for about 30 seconds removes a good portion of the added salt without meaningfully changing the protein content.
How Black Beans Compare to Other Legumes
Black beans hold their own against other legumes, but they’re not the most protein-dense option in the category. Lentils provide about 18 grams of protein per cooked cup, and they do it in fewer calories (around 138 per cup). That gives lentils a clear edge if you’re trying to maximize protein without adding extra calories.
Chickpeas and soybeans also tend to rank higher in protein quality scores, which measure how well your body can actually use the protein based on its amino acid profile and digestibility. Black beans score solidly in the middle of the legume range on these measures. Their limiting amino acid is methionine, one of the sulfur-containing amino acids that most legumes are low in. Grains like rice happen to be rich in methionine, which is exactly why rice and beans is such a nutritionally effective combination.
Protein Quality and Completeness
Not all protein is created equal. Your body needs nine essential amino acids to build and repair tissue, and most animal proteins deliver all nine in the right proportions. Black beans provide generous amounts of lysine (an amino acid that grains lack) but fall short on methionine and cysteine. This doesn’t mean the protein is wasted. It means your body uses it most efficiently when you pair black beans with a complementary protein source.
You don’t need to eat these combinations in the same meal. As long as you’re eating a varied diet throughout the day that includes grains, nuts, or seeds alongside your beans, your body pools those amino acids and uses them as needed. A diet built around black beans, rice, tortillas, vegetables, and the occasional handful of seeds covers the full spectrum without any animal protein required.
Soaking and Cooking Affect What You Absorb
Raw and undercooked beans contain compounds called phytates and lectins that can interfere with how well your body absorbs protein and minerals. Phytates bind to minerals in your digestive tract, and lectins can irritate the gut lining if consumed in large quantities. The good news is that standard preparation methods neutralize most of these compounds.
Soaking dried black beans overnight and then boiling them breaks down the majority of lectins and reduces phytate levels substantially. Sprouting beans before cooking goes even further, boosting both mineral availability and protein digestibility. Pressure cooking is another effective method, as the high heat and steam degrade antinutrient compounds more quickly than stovetop simmering. Even canned beans, which have been commercially pressure-cooked, have low enough levels of these compounds that absorption isn’t a practical concern.
Other Nutrients Worth Noting
People searching for protein content are often evaluating black beans as a protein source, so it’s worth knowing what else comes along for the ride. A cup of cooked black beans delivers roughly 15 grams of fiber, which is more than half of what most adults need daily. They’re also rich in folate, iron, magnesium, and potassium.
The fiber content is particularly relevant if you’re comparing black beans to animal protein sources, which contain zero fiber. That fiber slows digestion, helps stabilize blood sugar after meals, and feeds beneficial gut bacteria. The trade-off is that black beans come with more carbohydrates than animal proteins. One cup contains about 40 grams of carbs, roughly 15 of which are fiber. If you’re tracking macros on a low-carb diet, that’s a meaningful amount. If you’re simply trying to hit a protein target on a budget, black beans remain one of the cheapest ways to do it, typically costing well under a dollar per serving when bought dried.