Asparagus and beans: one has the trials, one has the folate

Across 38 randomized trials with 2095 people, eating whole pulses at a median 130 g a day for 6 weeks lowered LDL cholesterol by 5.4 mg/dL (95% CI 3.1 to 7.3; metric: 0.14 mmol/L, 0.08 to 0.19), a lipid marker from short trials that did not count heart events. That is the bean side. We found no trial of the whole asparagus vegetable on any health outcome, and no study that compares the two foods. What asparagus has is folate. Across 8 USDA samples, raw green asparagus averaged 182.5 mcg per 3.5 oz (100 g), ranging from 143 to 206.6 mcg. By the USDA retention factor for boiled vegetables, a general figure never measured on asparagus, about 65 percent of folate stays after boiling and draining. Dry cannellini beans averaged 6.7 mg of iron per 3.5 oz (100 g) and canned drained ones 1.4 mg, a gap that is mostly water taken up in cooking.

How much is actually in it

• Across 8 USDA samples, raw green asparagus averaged 182.5 mcg of folate per 3.5 oz (100 g), ranging from 143 to 206.6 mcg. — USDA Foundation Foods samples of Asparagus, green, raw (n = 8 samples) Evidence E source
  Folate 182.5 mcg per 3.5 oz (100 g), range 143.0 to 206.6 (median 188.5), spread 35%
• Dry cannellini beans averaged 6.7 mg of iron per 3.5 oz (100 g) across 8 USDA samples, while canned drained cannellini averaged 1.4 mg, mostly because cooked beans carry water. — USDA Foundation Foods samples of Beans, cannellini, dry and canned, sodium added, drained (n = 8 samples each) Evidence E source
  Iron 6.673 mg per 3.5 oz (100 g) dry (range 5.26 to 8.57); 1.405 mg canned drained (range 1.08 to 1.77); spread about 50% in both
• The NIH Office of Dietary Supplements lists asparagus among the foods with the highest folate levels, alongside spinach, liver and brussels sprouts. — US foods, NIH ODS folate fact sheet for health professionals Evidence E source
  Asparagus named among the highest folate foods

What your body absorbs

• In stable-isotope studies in young women, only 2.5% of the iron in whole red bean porridge was absorbed, and removing both polyphenols and phytic acid raised absorption 2.6-fold. — young women, 6 iron isotope absorption studies of 16 or 17 participants each (n = 16 to 17 per study) Evidence B source
  Iron absorption 2.5% from whole bean porridge; 2.6-fold higher after polyphenol and phytate removal; 50 mg bean polyphenols cut absorption by 14%, 200 mg by 45%
• In 9 volunteers with an intestinal tube, protein from cooked dehulled faba beans was 84.1% digestible, and histidine and tryptophan limited its quality. — 9 healthy adults (7 men, 2 women) with a naso-ileal tube, single 250 g cooked faba bean meal with 20 g protein (n = 9) Evidence C source
  Ileal nitrogen digestibility 84.1% (SD 7.7); mean amino acid digestibility 89.8%; DIAAS 0.77 (N x 5.4)
• In 19 women, calcium from young winged bean pods was absorbed at 39% against 55% from milk, lowered partly by phytate, oxalate and fiber. — 19 healthy Thai women aged 20 to 45, 3-way randomized crossover, about 100 mg calcium per meal (n = 19) Evidence B source
  Fractional calcium absorption 0.391 winged bean pods, 0.476 ivy gourd, 0.552 milk

What cooking and storage change

• By the USDA retention table for Vegetables and Vegetable Products boiled in covering water and drained, 65% of folate, 80% of thiamin and 90% of potassium stay in the vegetable. — USDA Release 6 group factor for Vegetables and Vegetable Products, method 3775 (n = group factor) Evidence E source
  Retention folate 65%, thiamin 80%, potassium 90%
• By the USDA retention table for Legumes and Legume Products boiled 45 to 75 minutes and drained, 45% of folate, 60% of thiamin, 70% of potassium and 80% of iron stay in the beans. — USDA Release 6 group factor for Legumes and Legume Products, method 521 (n = group factor) Evidence E source
  Retention folate 45%, thiamin 60%, potassium 70%, iron 80%

What it does to your health

• Across 38 randomized trials with 2095 people, eating whole pulses (median 130 g a day for 6 weeks) lowered LDL cholesterol by 5.4 mg/dL (0.14 mmol/L). — adults in 38 randomized trials of whole dietary pulses lasting at least 3 weeks, median 6 weeks (n = 2095) Evidence A source
  LDL cholesterol -5.4 mg/dL (95% CI -7.3 to -3.1; metric: -0.14 mmol/L, -0.19 to -0.08); non-HDL cholesterol -8.5 mg/dL (-0.22 mmol/L); apoB -0.08 g/L; HDL cholesterol -1.2 mg/dL (-0.03 mmol/L); no effect on other lipids
• A review of prospective studies and trials for the Nutrition and Chronic Diseases Expert Group placed beans and legumes among 10 foods with probable or convincing causal protection against cardiometabolic disease. — adults in meta-analyses of prospective cohorts and RCTs, searched to May 2015 (n = 23 meta-analyses included) Evidence C source
  Beans/legumes on the list of protective foods; no single effect size in the abstract

Safety, limits and interactions

• A systematic review describes the lectins in common beans as anti-nutritional factors that can cause intestinal disorders. — laboratory, animal and limited human studies of Phaseolus vulgaris lectins Evidence D source
  No dose-response in humans in the abstract
• Asparagus or bean extracts sold as dietary supplements in the US fall under DSHEA (1994), so the FDA does not approve them for safety or effectiveness before they are sold. — Dietary supplements sold in the United States Evidence E source
  No FDA premarket approval of safety, effectiveness or labeling

What people believe that the data does not support

• The European Union refused the claim that asparagus supports the excretory function of the kidneys and contributes to urinary flow. — European Union food labeling, claim on Asparagus officinalis Evidence E source
  POL-HC-6652 non-authorized; no authorized claim for asparagus or beans in the register

Who this works differently for

• In 20 women, a bean line bred with 90% less phytic acid gave 6.1% iron absorption, 60% more than its normal parent bean. — 20 young women, paired double meal crossover with stable iron isotopes (n = 20) Evidence B source
  Fractional iron absorption 6.1% (95% CI 2.6 to 14.7) from the low-phytate high-polyphenol line, 60% higher than the parent (P < 0.001)

The bottom line

Bean iron is hard to absorb. In stable-isotope studies in young women, only 2.5 percent of the iron in a whole red bean porridge was absorbed, and removing both polyphenols and phytic acid raised that 2.6-fold. A bean line bred with less phytic acid gave 6.1 percent absorption in 20 women (95% CI 2.6 to 14.7), 60 percent more than its parent, and it is an experimental line you will not find in a shop. In 9 volunteers with an intestinal tube, protein from one meal of cooked faba beans was 84.1 percent digestible at the end of the small intestine. In 19 Thai women, calcium from young winged bean pods was absorbed at 39 percent against 55 percent from milk. For asparagus we found no absorption study at all. Boiling costs beans more than it costs vegetables. By the USDA group factor for legumes boiled 45 to 75 minutes and drained, 45 percent of folate, 60 percent of thiamin and 80 percent of iron stay in the beans. A review for the Nutrition and Chronic Diseases Expert Group placed beans and legumes among 10 foods with probable or convincing causal protection against cardiometabolic disease, a judgement built mostly on observational data with no single effect size. The EU refused the claim that asparagus supports the kidneys and urinary flow, and it holds no authorized claim for beans. The one safety card is about beans. A systematic review describes the lectins in common beans as anti-nutritional factors that can cause intestinal disorders, drawing on laboratory, animal and limited human studies. Heat destroys the lectin, so the concern is dry beans eaten raw or undercooked, and we have no card yet on the soaking and boiling that make them safe. We have no card on allergy, pregnancy, children or medicines for either food.

Sources

1. asbn-r4-01 · USDA FoodData Central Foundation Foods, dataset
   Asparagus, green, raw (USDA Foundation Foods, release 2026-04-30): folate, total 182.5 ug per 100 g; range 143.0-206.6 (median 188.5); samples 8; spread 35%
   USDA FoodData Central, Foundation Foods, release 2026-04-30, Asparagus, green, raw · checked 2026-09-29
2. asbn-r4-02 · USDA FoodData Central Foundation Foods, dataset
   Beans, cannellini, dry: Iron, Fe 6.673 mg per 100 g, range 5.26-8.57 (median 6.565), samples 8, spread 50%; Beans, cannellini, canned, sodium added, drained: Iron, Fe 1.405 mg, range 1.08-1.77 (median 1.33), samples 8, spread 49% (USDA Foundation Foods, release 2026-04-30)
   USDA FoodData Central, Foundation Foods, release 2026-04-30, Beans, cannellini · checked 2026-09-29
3. asbn-r4-12 · fact sheet
   Spinach, liver, asparagus, and brussels sprouts are among the foods with the highest folate levels.
   NIH Office of Dietary Supplements, Folate Fact Sheet for Health Professionals · checked 2026-09-29
4. asbn-r4-07 · RCT
   The mean iron absorption from whole bean porridge was 2.5%. PP and PA removal increased absorption 2.6-fold (P < 0.001) and removal of PP from dephytinized porridge doubled absorption (P < 0.001).
   J Nutr, 2010 · checked 2026-09-29
5. asbn-r4-09 · clinical trial
   The ileal N digestibility was 84.1% ± 7.7%.
   J Nutr, 2024 · checked 2026-09-29
6. asbn-r4-10 · randomized crossover trial
   Fractional calcium absorption (X+/- SD) was 0.391 +/- 0.128 from winged beans, 0.476 +/- 0.109 from ivy gourd, and 0.552 +/- 0.119 from milk.
   J Food Sci, 2008 · checked 2026-09-29
7. asbn-r4-03 · USDA Retention Factors Release 6, dataset
   3775 Vegetables and Vegetable Products VEG,OTHER,BLD,WATER COVER,DRAINED: folate_total_ug 65%; thiamin_mg 80%; potassium_mg 90%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), method 3775 · checked 2026-09-29
8. asbn-r4-04 · USDA Retention Factors Release 6, dataset
   521 Legumes and Legume Products LEGUMES,CKD 45/75MIN,BOILED,DRND: folate_total_ug 45%; thiamin_mg 60%; potassium_mg 70%; iron_mg 80%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), method 521 · checked 2026-09-29
9. asbn-r4-05 · meta-analysis of RCTs
   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]), non-high-density lipoprotein-cholesterol (-0.22 mmol/L [95% CI, -0.30 to -0.14]), apoB (apolipoprotein B) (-0.08 g/L [95% CI, -0.13 to -0.03]) and high-density lipoprotein-cholesterol (-0.03 mmol/L [95% CI, -0.05 to -0.01]) with no effects on other lipids.
   J Am Heart Assoc, 2026 · checked 2026-09-29
10. asbn-r4-06 · systematic review
    We identified 10 foods and 7 nutrients with evidence for causal cardiometabolic effects, including protective effects of fruits, vegetables, beans/legumes, nuts/seeds, whole grains, fish, yogurt, fiber, seafood omega-3s, polyunsaturated fats, and potassium; and harms of unprocessed red meats, processed meats, sugar-sweetened beverages, glycemic load, trans-fats, and sodium.
    PLoS One, 2017 · checked 2026-09-29
11. asbn-r4-11 · systematic review
    Studies have shown that lectins are anti-nutritional factors that can cause intestinal disorders.
    Crit Rev Food Sci Nutr, 2018 · checked 2026-09-29
12. sf-dshea-2 · agency advice
    The Federal Food, Drug, and Cosmetic Act was amended in 1994 by the Dietary Supplement Health and Education Act, often referred to as DSHEA, which defined “dietary supplement” and set out the FDA’s authority regarding such products....The FDA does NOT have the authority to approve dietary supplements for safety and effectiveness, or to approve their labeling, before the supplements are sold to the public.
    FDA, FDA 101: Dietary Supplements · checked 2026-10-08
13. asbn-r4-13 · regulatory register entry
    POL-HC-6652 Asparagus officinalis Supports the excretory function of the kidneys /contributes to urinary flow Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6652, snapshot 2026-09-21 · checked 2026-09-29
14. asbn-r4-08 · randomized crossover trial
    Fractional iron absorption from the lpa bean high in PPs was 6.1% (95% CI: 2.6, 14.7), which was 60 and 130% higher compared with the parent high in PPs (P < 0.001) and low in PPs (P < 0.001), respectively.
    J Nutr, 2013 · checked 2026-09-29