Black beans and pinto beans: close cousins tested in small trials

Every trial on this page is small, and most measured a single meal. The longest ran 6 weeks in Canadian adults with mildly high cholesterol, with about 60 people per arm. A daily mix of four beans, black and pinto among them, lowered LDL cholesterol by 0.21 (95% CI -0.39 to -0.03) against rice, in units the abstract leaves unstated, while peas did not reach significance. Because the beans were mixed, it cannot say which of the two did more. In 17 adults with type 2 diabetes, most of them on metformin, pinto bean and black bean meals with rice both gave a lower blood glucose area than rice alone, and kidney beans did not. A cooked cup of either weighs 6.3 oz (180 g).

How much is actually in it

• CoFID lists dried pinto beans at 21.1 g protein and 5.4 mg iron per 3.5 oz (100 g) raw, and 8.9 g protein and 2.3 mg iron per 3.5 oz (100 g) boiled, mostly because boiled beans hold 62.5 g water. — — Evidence E source
  Raw 327 calories, protein 21.1 g, iron 5.40 mg, folate 520 ug, water 10.6 g; boiled 137 calories, 8.9 g, 2.30 mg, 145 ug, 62.5 g

What a real portion looks like

• FNDDS weighs 1 cup of cooked black beans and of cooked pinto beans (from dried, no fat) at 180 g, and 1 oz dry yields 70 g cooked. — — Evidence E source
  1 cup 180 g, 1 oz dry yield 70 g, quantity not specified 90 g, same for both beans

What your body absorbs

• In two crossover RCTs in 55 young and older adults, two ounce-equivalents of black beans supplied 3.02 g essential amino acids versus 7.36 g from pork and gave lower EAA bioavailability. — 30 young (mean 26 y) and 25 older (mean 64 y) adults, single meals, 300 min sampling (n = 55) Evidence B source
  EAA content 3.02 g (black beans) vs 7.36 g (pork) and 5.38 g (eggs), bioavailability lower, p < 0.0001
• In a crossover RCT of 20 adults using a dual tracer method, lysine and threonine uptake from 20 g black bean protein did not differ between older and young adults (P = 0.849), unlike sorghum (19% lower). — 10 young (21.8 y) and 10 older (72.8 y) adults, 20 g labeled protein per test day (n = 20) Evidence B source
  Black beans P = 0.849 older vs young, sorghum 19% lower (P = 0.041)
• In a stable-isotope crossover in Guatemalan girls aged 12-13, iron absorption from fortified corn tortilla and black bean paste meals was 5.5% with ferrous sulfate and 9.0% with NaFeEDTA. — Guatemalan girls aged 12-13, erythrocyte incorporation 14 d after intake Evidence B source
  Geometric mean 5.5% (ferrous sulfate) vs 9.0% (NaFeEDTA), P = 0.009

What cooking and storage change

• A survey of rural households in Guatemala found beans are usually cooked without soaking, and few cooks add salt at the start of cooking. — 10 families from each of 19 municipalities, northeastern Guatemala (n = 190) Evidence C source
  32% attributed hard-to-cook beans to storage time
• USDA retention factors for legumes boiled 2 to 2.5 h and drained keep 30% of folate, 40% of thiamin and 75% of iron. — — Evidence E source
  Folate 30%, thiamin 40%, vitamin B6 50%, potassium 65%, magnesium 70%, iron 75%, zinc 85% retained

What it does to your health

• In a crossover RCT in 8 healthy adults, pulse wave velocity was lower 6 h after black beans than after pinto beans, and blood pressure and PWV were lower 2 h after pinto beans than after navy beans. — 8 healthy adults, single meals of 3/4 cup beans or rice, measured to 6 h (n = 8) Evidence B source
  PWV lower after black vs pinto bean at 6 h (p < 0.05), no effect sizes in abstract
• In the same 17-person type 2 diabetes crossover, pinto and black bean rice meals both lowered glucose iAUC versus rice over 0-180 min, with medium effect sizes (d about 0.4 to 0.5). — 17 adults with type 2 diabetes, 50 g available carbohydrate test meals (n = 17) Evidence B source
  0-120 min P = 0.009 (pinto) and 0.002 (black), Cohen d 0.431 (0-120) and 0.501 (0-180)
• In a crossover RCT in 12 healthy women, a black bean and rice meal gave lower blood glucose than rice alone at 60, 90 and 120 min. — 12 healthy adult women aged 18-65, 50 g available carbohydrate meals (n = 12) Evidence B source
  Glucose change lower at 60 min (p = 0.026), 90 min (p = 0.001), 120 min (p = 0.024)
• In a 6-week RCT in adults with mild hypercholesterolemia, a daily bean mix including black and pinto beans lowered LDL cholesterol by 0.21 versus rice, while peas did not. — adults with mild hypercholesterolemia, about 60 per arm, 6 weeks, Canada (n = 180) Evidence B source
  LDL -0.21 (95% CI -0.39 to -0.03) vs rice, peas -0.11 (95% CI -0.29 to 0.07)

Safety, limits and interactions

• Observational data from 90 canned pinto and fava bean samples in Iran found cadmium below the EU limit of 0.1 mg/kg and negligible non-carcinogenic risk for 95% of consumers. — 90 canned pinto and fava bean samples, Gilan Province, Iran, 2023 (n = 90) Evidence C source
  Max cadmium below 0.1 mg/kg, cadmium in pinto 0.004 mg/kg

What people believe that the data does not support

• Across 3 feeding trials of 1/2 cup beans a day for 8-12 weeks, fewer than 50% reported more flatulence from pinto beans in the first week, and 3-11% did so even on control diets. — adults in 3 trials (n = 17, 29 and 80), 1/2 cup beans daily for 8 or 12 weeks (n = 126) Evidence B source
  <50% increased flatulence week 1 with pinto or baked beans, 19% with black-eyed peas, 3-11% on control

Who this works differently for

• In a crossover RCT in 17 adults with type 2 diabetes, pinto bean and black bean meals with rice (50 g available carbohydrate) gave a lower glucose area under the curve than rice alone. — 17 men and women with type 2 diabetes aged 35-70, single breakfast test meals (n = 17) Evidence B source
  IAUC lower for pinto/rice and black/rice vs rice alone, not for kidney beans
• In a crossover RCT in 35 older adults, a black bean breakfast tortilla gave appetite ratings and 24 h energy intake not significantly different from a beef breakfast. — 35 older adults, mean age 72.4 y, single test breakfasts (n = 35) Evidence B source
  No significant difference in appetite AUCs, ad libitum lunch or 24 h energy intake vs beef
• In a crossover RCT in 12 adults with metabolic syndrome, adding black beans to a Western-style meal lowered postprandial insulin versus fiber-matched and antioxidant-matched meals. — 12 adults with metabolic syndrome, single meals, 5 h postprandial (n = 12) Evidence B source
  Insulin lower after black bean meal vs FM or AM meals (p < 0.0001)
• In a crossover pilot in 9 adults with arterial stiffness, systolic blood pressure rose 4% after white rice but not after a black bean meal. — 9 adults aged 50-64 with arterial stiffness, single meals, 2 h (n = 9) Evidence B source
  Systolic BP +4% after rice, no rise after black beans or wheat

The bottom line

The glucose effects repeat in other single meals. In 12 healthy women, a black bean and rice meal kept blood glucose lower than rice alone at 60, 90 and 120 minutes. In 12 adults with metabolic syndrome, insulin was lower after a black bean meal than after meals matched for fiber or antioxidants (p < 0.0001). In 9 adults aged 50 to 64 with stiff arteries, systolic blood pressure rose 4% after white rice and did not rise after beans. One pilot of 8 healthy adults found pulse wave velocity lower 6 hours after black beans than after pinto beans, a single unreplicated result with many comparisons. In 35 adults with a mean age of 72, a black bean breakfast left appetite and 24-hour energy intake not significantly different from a beef breakfast, which falls short of proving the two equal. As protein, beans give less per portion. Two ounce-equivalents of black beans supplied 3.02 g of essential amino acids against 7.36 g from pork and 5.38 g from eggs, with lower bioavailability, in 55 young and older adults eating the same portion rather than the same protein. Lysine and threonine uptake from black bean protein did not differ between 10 older and 10 young adults (P = 0.849). In Guatemalan girls aged 12 to 13, a fortified corn tortilla and black bean paste meal gave 5.5% iron absorption with ferrous sulfate and 9.0% with NaFeEDTA, and the beans were not tested apart from the corn. Cooking matters for the numbers. The UK table lists dried pinto beans at 21.1 g of protein and 5.4 mg of iron per 3.5 oz (100 g) raw, and 8.9 g and 2.3 mg per 3.5 oz (100 g) boiled, mainly because boiled beans are 62.5% water. It has no black bean entry. USDA factors for legumes boiled 2 to 2.5 hours and drained keep 30% of folate, 40% of thiamin and 75% of iron, figures for the legume group from a 1975 table. In rural Guatemala, beans are usually cooked without soaking. Gas is less certain than its reputation. Across 3 trials of half a cup of beans a day, fewer than 50% reported more flatulence from pinto or baked beans in the first week, and 3% to 11% reported it on control diets with no beans. Black beans were not tested there. In 90 canned pinto and fava bean samples from one Iranian province, cadmium stayed below the EU limit of 0.1 mg/kg, with negligible non-carcinogenic risk for 95% of consumers. We have no card on pregnancy, children as a caution, kidney disease or medicines for either bean.

Sources

1. bpcmp-r4-15 · food composition dataset
   Beans, pinto, dried, raw (CoFID 13-106): energy 327 kcal, protein 21.1 g, iron 5.40 mg, folate 520 ug, water 10.6 g per 100 g; Beans, pinto, dried, boiled in unsalted water (CoFID 13-107): energy 137 kcal, protein 8.9 g, iron 2.30 mg, folate 145 ug, water 62.5 g per 100 g
   CoFID 2021, Public Health England, codes 13-106 and 13-107 · checked 2026-09-29
2. bpcmp-r4-17 · food composition dataset
   Black beans, from dried, no added fat (FNDDS 41102020, fdc 2707361) and Pinto beans, from dried, no added fat (FNDDS 41104020, fdc 2707373): 1 cup = 180 g; 1 oz dry, yield after cooking = 70 g; quantity not specified = 90 g
   USDA FNDDS 2021-2023, codes 41102020 and 41104020 · checked 2026-09-29
3. bpcmp-r4-06 · 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
4. bpcmp-r4-07 · 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
5. bpcmp-r4-08 · randomized crossover trial
   Geometric mean iron bioavailability from test meals fortified with ferrous sulfate was 5.5% and was significantly higher in test meals fortified with NaFeEDTA (9.0%; P = 0.009, paired t test).
   Am J Clin Nutr, 2002 · checked 2026-09-29
6. bpcmp-r4-14 · cross-sectional survey
   With respect to cooking practices, it was found that beans are not usually soaked prior to cooking, and that few housewives add salt at the beginning of cooking.
   Arch Latinoam Nutr, 1988 · checked 2026-09-29
7. bpcmp-r4-16 · food composition dataset
   LEGUMES,CKD 2/2.5HRS,BOILED,DRAINED (USDA-RETN-R6:541, group 16): folate_total_ug 30%, thiamin_mg 40%, vitamin_b6_mg 50%, potassium_mg 65%, magnesium_mg 70%, iron_mg 75%, zinc_mg 85% retained
   USDA Table of Nutrient Retention Factors, Release 6 (2007), Retn_Code 541 · checked 2026-09-29
8. bpcmp-r4-01 · randomized crossover trial
   Blood pressure and pulse wave velocity (PWV) were lower at 2 h following red kidney bean and pinto bean consumption compared to rice and navy bean, respectively (p < 0.05). 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
   Nutr Metab Cardiovasc Dis, 2021 · checked 2026-09-29
9. bpcmp-r4-03 · randomized crossover trial
   Significant differences were found between the rice control meal and the pinto beans and rice and black beans and rice at 0–120 (P = 0.009 and 0.002) and 0–180 minutes (P = 0.017 and 0.007). The effect sizes (Cohen’s d) for iAUC were determined to be 0.431 for 0–120 minutes and 0.501 for 0–180 minutes.
   Nutr J, 2012 · checked 2026-09-29
10. bpcmp-r4-04 · 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
11. bpcmp-r4-05 · randomized controlled trial
    Mean LDL-cholesterol was lower in the bean group (-0.21; 95% CI: -0.39, -0.03) but not the pea group (-0.11; 95% CI: -0.29, 0.07) relative to rice after 6 wk.
    J Nutr, 2024 · checked 2026-09-29
12. bpcmp-r4-13 · cross-sectional study
    In this study, the maximum measured cadmium level was below the EU standard limit (0.1 mg/kg)... The non-carcinogenic risk was negligible for 95% of consumers
    Sci Rep, 2026 · checked 2026-09-29
13. bpcmp-r4-09 · randomized trials, self-report
    Less than 50% reported increased flatulence from eating pinto or baked beans during the first week of each trial, but only 19% had a flatulence increase with black-eyed peas. A small percentage (3-11%) reported increased flatulence across the three studies even on control diets without flatulence-producing components.
    Nutr J, 2011 · checked 2026-09-29
14. bpcmp-r4-02 · randomized crossover trial
    Incremental area under the curve values were significantly lower for the pinto and black bean/rice meals compared to rice alone, but not for kidney beans.
    Nutr J, 2012 · checked 2026-09-29
15. bpcmp-r4-10 · randomized crossover trial
    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
16. bpcmp-r4-11 · randomized crossover trial
    Insulin was lower after the BB meal, compared to the FM or AM meals (p < 0.0001).
    Nutrients, 2015 · checked 2026-09-29
17. bpcmp-r4-12 · randomized crossover trial
    Peripheral and central systolic blood pressure was increased (4%) after eating white rice but not after the consumption of wheat or beans.
    Nutrients, 2025 · checked 2026-09-29