Black beans and kidney beans: near twins on the plate, one cooking rule

Black and kidney beans are both common beans, Phaseolus vulgaris, and a meta-analysis of 23 clinical trials of that species found LDL cholesterol 19 percent lower with bean intake. The trials mixed whole beans with bean extracts and several varieties, and the abstract gives no confidence interval, so read 19 percent as a direction with a rough size. On the plate the two are close. Canned black beans, drained and rinsed, hold 6.9 g protein per 3.5 oz (100 g) and canned dark red kidney beans 7.8 g. US survey coding counts a cup of either, cooked from dried, as 180 g. The difference that matters in the kitchen is safety. FDA warns that as few as four or five raw red kidney beans can cause illness, and that slow cookers should not be used for them.

How much is actually in it

• Canned black beans, drained and rinsed, hold 6.9 g protein and 0.34 mg copper per 3.5 oz (100 g), and sodium ranged from 53 to 280 mg between samples. — Canned black beans, sodium added, drained and rinsed, 8 USDA samples Evidence E source
  Protein 6.912 g, copper 0.336 mg, sodium 217.9 mg per 3.5 oz (100 g) (sodium range 53.4-280)
• Canned dark red kidney beans, drained and rinsed, hold 7.8 g protein, 0.27 mg copper and 104 mg phosphorus per 3.5 oz (100 g), close to black beans. — Canned dark red kidney beans, sodium and sugar added, drained and rinsed, USDA samples Evidence E source
  Protein 7.8 g, copper 0.273 mg, phosphorus 104.1 mg per 3.5 oz (100 g)
• UK boiled red kidney beans give 100 calories, 8.6 g protein and 11.1 g fiber per 3.5 oz (100 g). — Red kidney beans, dried, boiled in unsalted water, 100 g Evidence E source
  Energy 100 calories, protein 8.6 g, AOAC fiber 11.1 g, carbohydrate 15.1 g per 3.5 oz (100 g)

What a real portion looks like

• US survey coding counts a cup of black beans cooked from dried at 180 g, and 1 oz of dry beans yields 70 g cooked. — US portion measures, FNDDS Evidence E source
  1 cup 180 g, 1 oz dry yields 70 g cooked, quantity not specified 90 g
• US survey coding uses the same 180 g cup for kidney beans cooked from dried, so portions of the two beans are directly comparable. — US portion measures, FNDDS Evidence E source
  1 cup 180 g, 1 oz dry yields 70 g cooked, quantity not specified 90 g

What your body absorbs

• In 10 young and 10 older adults, black bean protein was digested equally well at both ages, while sorghum protein was digested 19% less by older adults. — 10 young (about 22 y) and 10 older (about 73 y) adults, 20 g labeled protein per test (n = 20) Evidence B source
  Lysine and threonine plasma-to-meal ratio: black beans no age difference (P = 0.849), sorghum -19% in older adults (P = 0.041)
• In 10 adults eating a typical Jamaican meal, essential amino acids from red kidney beans were on average 79% digestible, giving a protein score of 0.63 limited by methionine. — 10 healthy adults (5 men, 5 women), single meal with labeled red kidney beans (n = 10) Evidence C source
  Mean IAA digestibility 79.4% (threonine 69.0% to lysine 85.7%), extrapolated DIAAS 0.63

What cooking and storage change

• Lab and review data show that Phaseolus beans, including kidney beans, contain lectins that act as hemagglutinins and can cause intestinal disorders, and heating is among the treatments that can eliminate them. — Phaseolus vulgaris lectins, review of laboratory and animal research Evidence D source
  Lectins are anti-nutritional and toxic hemagglutinins, heating affects their activity
• FDA warns that as few as four or five raw red kidney beans can cause illness, and that slow cookers should not be used for these beans because they may not get hot enough to destroy the lectin. — Consumers of raw, soaked or undercooked red kidney beans Evidence E source
  Raw beans 20,000-70,000 hau vs 200-400 hau fully cooked, slow cookers often reach only 75 C or less

What it does to your health

• A meta-analysis of 23 clinical trials of common beans, the species that includes black and kidney beans, found LDL cholesterol 19% lower with bean intake. — Adults in clinical and randomized trials of whole beans or bean extracts (n = 23 studies) Evidence B source
  LDL cholesterol -19%, CVD risk -11%, CHD risk -22%
• In 12 healthy women, swapping part of a white rice meal for black beans at the same 50 g of carbohydrate lowered blood glucose at 60, 90 and 120 minutes. — Healthy adult women aged 18-65, single test meals at least 7 days apart (n = 12) Evidence B source
  Lower glucose vs rice at 60 min (p = 0.026), 90 min (p = 0.001) and 120 min (p = 0.024)
• In a pilot trial in 8 healthy adults, 3/4 cup of black or red kidney beans relaxed blood vessels more than rice or lighter beans over 6 hours. — 8 healthy adults, single 3/4 cup servings at least 6 days apart (n = 8) Evidence B source
  Lower wave reflection magnitude after red kidney and black beans vs rice, navy and pinto beans (p < 0.05)

What people believe that the data does not support

• Two US protein ounce-equivalents of black beans supplied 3.02 g essential amino acids against 7.36 g from pork, and delivered less to the blood in both young and older adults. — Young (n 30) and older (n 25) adults, standardized meals with two ounce-equivalents (n = 55) Evidence B source
  EAA content 3.02 g black beans vs 7.36 g pork and 5.38 g eggs, lower postprandial EAA bioavailability (p < 0.0001)

Who this works differently for

• In 35 older adults, a breakfast with 4.8 oz (135 g) of black or red kidney beans was as filling as one with 2.8 oz (80 g) of beef, with no difference in later food intake. — Older adults aged about 72, breakfast tortilla test meals (n = 35) Evidence B source
  No significant difference in appetite AUCs, ad libitum lunch or 24 h energy intake between beans and beef
• In 9 adults with stiff arteries, 3/4 cup of black beans did not lower arterial stiffness at 2 hours, while whole wheat kernels cut it from 26.1% to 16.2%. — Adults aged 50-64 with established arterial stiffness, single servings (n = 9) Evidence B source
  Augmentation index unchanged after beans, 26.1% to 16.2% after whole wheat, systolic pressure +4% after white rice only

The bottom line

Black beans blunted the glucose rise of a rice meal. In 12 healthy women, replacing part of a white rice meal with black beans at the same 50 g of carbohydrate gave lower glucose at 60, 90 and 120 minutes, in a randomized crossover test of single meals. In 35 adults around 72 years old, a breakfast with 4.8 oz (135 g) of black or red kidney beans was as filling as one with 2.8 oz (80 g) of beef, and later eating did not differ. A single breakfast cannot show the two are equivalent. Protein is where black beans trail pork. Two US protein ounce-equivalents of black beans supplied 3.02 g of essential amino acids against 7.36 g from pork, and delivered less to the blood over 5 hours in 55 young and older adults, although US guidelines count those portions as equal. Digestion itself held up with age. In 10 young and 10 older adults black bean protein was digested equally well at both ages, while sorghum protein was digested 19 percent less by the older group. Red kidney bean amino acids were 79 percent digestible in 10 adults eating one Jamaican meal, a nonrandomised study that gave a protein score of 0.63, limited by methionine. The blood vessel results are small pilots. In 8 healthy adults, 3/4 cup of black or red kidney beans lowered wave reflection over 6 hours more than rice, navy or pinto beans. In 9 adults aged 50 to 64 with stiff arteries, black beans did not lower arterial stiffness at 2 hours, and whole wheat kernels did. Canned black beans ranged from 53 to 280 mg sodium per 3.5 oz (100 g) across 8 USDA samples after draining and rinsing, so the brand matters. UK boiled red kidney beans give 100 calories and 11.1 g fiber per 3.5 oz (100 g). The caution is lectin. A review of mostly laboratory work says Phaseolus lectins act as hemagglutinins and can cause intestinal disorders, and heating is among the treatments that remove them. FDA puts raw beans at 20,000 to 70,000 hemagglutinating units against 200 to 400 when fully cooked, and notes that slow cookers often reach only 75 C or less. We found nothing on these beans in pregnancy, children or with medicines.

Sources

1. bkb-daily-r4-10 · reference dataset
   FDC 2644285 Beans, black, canned, sodium added, drained and rinsed: Protein 6.912 g · Copper, Cu 0.336 mg · Sodium, Na 217.9 mg per 100 g (sodium Foundation samples 53.4-280, n=8)
   USDA FoodData Central Foundation Foods, FDC 2644285 (Beans, black, canned, sodium added, drained and rinsed) · checked 2026-09-29
2. bkb-daily-r4-11 · reference dataset
   FDC 2644289 Beans, kidney, dark red, canned, sodium added, sugar added, drained and rinsed: Protein 7.8 g · Copper, Cu 0.273 mg · Phosphorus, P 104.1 mg per 100 g
   USDA FoodData Central Foundation Foods, FDC 2644289 (Beans, kidney, dark red, canned, sodium added, sugar added, drained and rinsed) · checked 2026-09-29
3. bkb-daily-r4-12 · reference dataset
   CoFID 13-659 Beans, red kidney, dried, boiled in unsalted water: Energy (kcal) 100 · Protein 8.6 g · AOAC fibre 11.1 g · Carbohydrate 15.1 g · Fat 1 g per 100 g
   CoFID 2021, Public Health England, code 13-659 (Beans, red kidney, dried, boiled in unsalted water) · checked 2026-09-29
4. bkb-daily-r4-13 · reference dataset
   FNDDS 2707361 Black beans, from dried, no added fat (food code 41102020): 1 cup 180 g · 1 oz dry, yield after cooking 70 g · Quantity not specified 90 g
   USDA FNDDS 2021-2023, food code 41102020, fdc_id 2707361 (Black beans, from dried, no added fat) · checked 2026-09-29
5. bkb-daily-r4-14 · reference dataset
   FNDDS 2707381 Kidney beans, from dried, no added fat (food code 41106020): 1 cup 180 g · 1 oz dry, yield after cooking 70 g · Quantity not specified 90 g
   USDA FNDDS 2021-2023, food code 41106020, fdc_id 2707381 (Kidney beans, from dried, no added fat) · checked 2026-09-29
6. bkb-daily-r4-04 · randomized crossover trial
   The isotope plasma-to-meal ratio for lysine and threonine was 19% lower in older adults compared with young adults for sorghum (P = 0.041), whereas it was not significantly different for milk (P = 0.277) and black beans (P = 0.849).
   Am J Clin Nutr, 2026 · checked 2026-09-29
7. bkb-daily-r4-06 · nonrandomised metabolic study
   Mean RKB-IAA digestibility (%) was 79.4 ± 0.5, ranging from 69.0 ± 1.2 (threonine) to 85.7 ± 1.7 (lysine).
   J Nutr, 2023 · checked 2026-09-29
8. bkb-daily-r4-09 · systematic review
   Studies have shown that lectins are anti-nutritional factors that can cause intestinal disorders. Owing to their ability to act as toxic allergens and hemagglutinins, the Phaseolus vulgaris lectins are of grave concern for human health and safety.
   Crit Rev Food Sci Nutr, 2018 · checked 2026-09-29
9. bkb-daily-r4-15 · agency guidance
   As few as four or five raw beans can trigger symptoms. ... Slow cookers should not be used to cook these beans or dishes that contain them.
   FDA Bad Bug Book, 2nd edition (2012), Phytohaemagglutinin chapter · checked 2026-09-29
10. bkb-daily-r4-01 · meta-analysis
    Findings indicated that common beans reduced LDL cholesterol by 19 percent, risk of cardiovascular disease (CVD) by 11 percent, and coronary heart disease (CHD) by 22 percent.
    Nutrients, 2021 · checked 2026-09-29
11. bkb-daily-r4-02 · randomized crossover trial
    Changes in blood glucose concentrations were significantly different for the black bean meal and the chickpea meal in comparison to rice alone at 60 min (p = 0.026 and p = 0.024), 90 min (p = 0.001 and p = 0.012) and 120 min post prandial (p = 0.024; black bean meal).
    Nutrients, 2017 · checked 2026-09-29
12. bkb-daily-r4-07 · randomized crossover trial
    There was greater vasorelaxation 6 h following consumption of darker-coloured beans, as shown by decreased vascular tone: PWV was lower after consuming black bean compared to pinto bean, augmentation pressure was lower after consuming black bean compared to rice and pinto bean, and wave reflection magnitude was lower after consuming red kidney bean and black bean compared to rice, navy bean, and pinto bean (p < 0.05).
    Nutr Metab Cardiovasc Dis, 2021 · checked 2026-09-29
13. bkb-daily-r4-05 · randomized crossover trial
    Two oz-eq portions of pork (7.36 g EAA) and eggs (5.38 g EAA) resulted in greater EAA bioavailability than black beans (3.02 g EAA) and almonds (1.85 g EAA) in young and older adults, separately or combined (p < 0.0001 for all).
    Nutrients, 2023 · checked 2026-09-29
14. bkb-daily-r4-03 · randomized crossover trial
    Older adults [n = 35, age 72.4 ± 6.66 y, BMI (in kg/m2) 25.1 ± 3.25] consumed 3 breakfast tortilla test meals containing 1 serving of black beans (135 g), red kidney beans (135 g), or beef (80 g) in a randomized, crossover design. ... Appetite sensation AUCs, ad libitum pizza intake, and 24-h energy intake did not significantly differ between the test meals.
    J Nutr, 2025 · checked 2026-09-29
15. bkb-daily-r4-08 · randomized crossover trial
    A marked decline in augmentation index at 75 bpm (arterial stiffness) from 26.1 ± 3.6% to 16.2 ± 2.0% was observed 2 h after eating whole wheat but not beans or white rice.
    Nutrients, 2025 · checked 2026-09-29