Black beans vs red beans: which has more protein?

Swapping one bean for the other barely changes the nutrition. The red beans here are red kidney beans. Boiled without salt, black beans have a little more fiber (8.7 g against 7.4 g per 3.5 oz, or 100 g), red kidney beans more iron (2.9 mg against 2.1 mg) and potassium. In 73 adults with high LDL, a daily cup of beans rotating black, dark red kidney and other beans lowered LDL cholesterol by about 8% over 4 weeks, while rice did not.

The real difference is in the pot. Beans carry a lectin that is highest in red kidney beans, and at the levels in raw beans it can cause nausea, severe vomiting and diarrhea. According to the FDA, four or five raw beans can be enough. From dry, soak red kidney beans for at least 5 hours, boil them in fresh water for at least 30 minutes and keep them out of the slow cooker. Canned kidney beans are safe.

Canned beans bring salt instead: 231 mg of sodium per 3.5 oz (100 g) of drained red kidney beans, 208 mg after rinsing, against 1 to 2 mg boiled at home.

The extra iron counts for less than it looks. In young women, only 2.5% of the iron in a red bean porridge was absorbed. Pick by taste and recipe.

The two beans are level on protein, about 15 g in a cooked cup of either, and in the trials we have, bean protein is less available than meat protein. In 10 healthy adults eating a red kidney bean meal, 79.4% of the essential amino acids were digested. In two randomized trials, two ounce-equivalents of black beans delivered 3.02 g of essential amino acids against 7.36 g from pork, and less of them reached the blood.

Evidence behind this note

1. Level E Boiled without salt, 3.5 oz (100 g) of black beans and red kidney beans are close: 132 vs 127 calories and about 8.7 to 8.9 g protein, with black beans higher in fiber and magnesium and red beans higher in iron and potassium. USDA SR Legacy 2019, FDC 173735 and 175194
2. Level B In a 4-week crossover RCT in 73 adults with high LDL, a daily cup (180 g) of canned beans including black and dark red kidney lowered LDL cholesterol by 8.1% against rice. J Nutr, 2021
3. Level E FDA's Bad Bug Book says the lectin phytohaemagglutinin occurs in many species of beans and is highest in red kidney beans, and advises boiling beans for at least 30 minutes and never cooking them, or dishes containing them, in a slow cooker. FDA, Bad Bug Book: Foodborne Pathogenic Microorganisms and Natural Toxins, 2nd edition, 2012, chapter Phytohaemagglutinin
4. Level E FDA says raw or undercooked kidney beans carry a lectin that causes nausea, severe vomiting and diarrhea, and that soaking 5 hours then boiling at least 30 minutes destroys it. US FDA, Natural Toxins in Food
5. Level E The FDA says as few as four or five raw kidney beans can trigger symptoms, raw beans carry 20,000 to 70,000 toxin units against 200 to 400 when fully cooked, and consumers should boil them for at least 30 minutes. US FDA, Bad Bug Book, 2nd edition, 2012, Phytohaemagglutinin chapter
6. Level E Home-boiled beans without salt carry 1 to 2 mg sodium per 3.5 oz (100 g), while canned red kidney beans carry 231 mg drained and 208 mg after rinsing, and low-sodium canned black beans 138 mg. USDA SR Legacy 2019, FDC 175194, 174285, 175243, 173735, 175237, 175238
7. Level B In stable-isotope studies in young women, only 2.5% of iron was absorbed from red bean porridge, and removing polyphenols and phytic acid raised absorption 2.6-fold. J Nutr, 2010
8. Level C In 10 healthy adults eating a Jamaican red kidney bean meal, about 79 percent of the essential amino acids were digested, with a protein quality score (DIAAS) of 0.63. J Nutr, 2023
9. Level B In two crossover RCTs in 30 young and 25 older adults, two ounce-equivalents of black beans delivered 3.02 g essential amino acids against 7.36 g from pork, with lower availability in the blood at any age. Nutrients, 2023
10. Level B In a crossover RCT in 17 adults with type 2 diabetes, black beans with rice lowered the glucose response against rice alone, while red kidney beans with rice lowered glucose at 90 to 150 minutes but not the total response. Nutr J, 2012

Written from the studies and agency guidance we hold for both foods, reviewed by the Bioma editorial system. How we verify.

Read more about these foods

• Black beans and red beans: nearly the same bean on the plate
• Black beans: half a cup a day, and the phytate costs you half your iron
• Red beans: a cholesterol food that must be boiled properly

Rankings and guides

• Which foods are highest in protein?
• Which foods give the most protein for the fewest calories?
• How much protein do you need per day?
• Protein: what it does and how much you need
• Protein: top food sources and Daily Value
• Black beans: full nutrition facts
• Red beans: full nutrition facts

More comparisons

• Black beans vs pinto beans
• Black beans vs refried beans

• Black beans: USDA FoodData Central, Beans, black, mature seeds, cooked, boiled, without salt, FDC ID 173735 · full profile · all forms of black beans
• Red beans: USDA FoodData Central, Beans, kidney, red, mature seeds, cooked, boiled, without salt, FDC ID 175194 · full profile · all forms of red beans

Each food is one USDA entry, chosen as it is usually eaten. Other cuts, brands and preparations differ; the links show them. % DV uses FDA Daily Values for adults. How we verify.