Black beans: half a cup a day, and the phytate costs you half your iron

Pulses lower LDL cholesterol, and unusually for nutrition there is a dose. Thirty-eight trials with a median of 130 grams a day, half to two thirds of a cup, give LDL down 0.14 mmol/L and apolipoprotein B down 0.08 g/L, with the relationship running linearly up to a full cup of beans. The authors add a detail worth repeating: no pulse anywhere in the world carries an authorised health claim for cholesterol, which is a fact about paperwork rather than about evidence. When beans were tested head-to-head against peas in one trial, the beans worked and the peas did not.

The numbers, per 100 g

How much is actually in it

• Beans lowered cholesterol and peas, tested the same way in the same trial, did not. — about 60 adults per group with mild hypercholesterolaemia (n = about 180) Evidence B source
  Against rice, LDL cholesterol was lower with beans (-0.21 mmol/L, 95% CI -0.39 to -0.03) but not with peas (-0.11, -0.29 to 0.07); non-HDL cholesterol (-0.20) and total cholesterol (-0.28) were also lower with beans; no change in triglycerides, glucose or insulin

What a real portion looks like

• Half a cup of pulses a day lowered LDL cholesterol, and the effect kept growing up to a full cup of beans. — 38 trials with 52 comparisons and 2095 participants, median duration 6 weeks and median dose 130 g a day (0.5 to 0.67 cup) (n = 2095) Evidence A source
  LDL cholesterol -0.14 mmol/L (95% CI -0.19 to -0.08), non-HDL cholesterol -0.22 (-0.30 to -0.14), apolipoprotein B -0.08 g/L (-0.13 to -0.03) and HDL cholesterol -0.03 (-0.05 to -0.01), with no effect on other lipids; results similar across pulse types; a linear inverse relationship for beans up to 1 cup a day (-0.25 mmol/L per half cup)
• A breakfast of black beans kept older adults as full as one made with beef. — 35 older adults, mean age 72.4, mean BMI 25.1 (n = 35) Evidence B source
  Fullness and satisfaction rose and hunger, desire to eat and prospective consumption fell after all three meals, with the bean meals not significantly different from beef

What your body absorbs

• Removing the phytic acid from beans raised the iron absorbed by half, which shows what the phytate is costing. — 22 Rwandese women with low iron status (n = 22) Evidence B source
  With native phytate, fractional absorption was 9.2% from control beans, 30% higher than from the biofortified beans (p<0.001), while the quantity absorbed from biofortified beans was still 19% higher (406 micrograms); removing about half the phytate raised the quantity absorbed to 599 micrograms (+37%) and removing over 95% raised it to 746 micrograms (+51%)

Who this works differently for

• In people who already have stiff arteries, wheat berries loosened them and black beans did not. — 9 adults aged 50 to 64 with established arterial stiffness, 3 men and 6 women (n = 9) Evidence B source
  Systolic pressure rose 4% after white rice but not after wheat or beans; the augmentation index at 75 bpm fell from 26.1% to 16.2% two hours after whole wheat but not after beans or rice; all foods slightly lowered heart rate

What is still unknown

• Six hours after a bowl of black beans, arteries were measurably more relaxed than after the same portion of rice. — 8 healthy adults (n = 8) Evidence B source
  At 2 hours blood pressure and pulse wave velocity were lower after red kidney and pinto beans than after rice and navy beans; at 6 hours the darker beans relaxed vessels more, with lower pulse wave velocity after black bean than pinto, lower augmentation pressure than rice and pinto, and lower wave reflection than rice, navy and pinto; LDL was lower 6 hours after black beans than rice

The bottom line

The iron question has a precise answer. In Rwandese women, removing more than 95 percent of the phytate from bean meals raised the quantity of iron absorbed by half. Breeding more iron into the bean also brought more phytate, and the two partly cancelled. Soaking and cooking at home are not the laboratory enzyme that was used, so this quantifies the barrier rather than removing it. Two smaller findings: black beans at breakfast kept older adults as full as beef, and six hours after a bowl of them arteries were measurably more relaxed than after rice, in eight people. Canning is the main thing that changes the numbers, with sodium running from 1 to 237 mg per 100 grams across our records.

Sources

1. blk-dr-02 · randomised 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 2026-09-22
2. blk-dr-01 · systematic review and dose-response meta-analysis of randomised controlled trials
   Thirty-eight trials (52 trial comparisons, n=2095) with a median of 6 weeks and dose of 130 g/d (0.5-0.67 cup/d) showed that whole dietary pulses decreased low-density lipoprotein-cholesterol (mean difference, -0.14 mmol/L [95% CI, -0.19 to -0.08])
   J Am Heart Assoc, 2026 · checked 2026-09-22
3. blk-dr-03 · randomised crossover trial
   Fullness and satisfaction were significantly increased, while hunger, desire to eat, and prospective food consumption were significantly decreased, following consumption of the black bean, red kidney bean, and beef test meals.
   J Nutr, 2025 · checked 2026-09-22
4. blk-dr-06 · crossover stable isotope absorption study
   With ∼50% and >95% dephytinization, the quantity of iron absorbed from the biofortified bean meals increased to 599 and 746 μg, respectively, which was 37% (P < 0.005) and 51% (P < 0.0001) higher
   J Nutr, 2014 · checked 2026-09-22
5. blk-dr-05 · randomised crossover pilot 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 2026-09-22
6. blk-dr-04 · randomised crossover pilot 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
   Nutr Metab Cardiovasc Dis, 2021 · checked 2026-09-22