Calcium on the label vs calcium absorbed
Spinach lists more calcium than bok choy, broccoli, green beans or carrot. Absorbed, it comes last: about 3 mg from a serving. Cooked kale lists 128 mg and delivers about 52.
Checked against its sources, in English and French, on 2026-10-17, with data v0.1. The text is as audited; any figure that comes from the live database is recomputed when the page loads and must still match it.
Audited with data v0.1 and method 2026-10-14. The site is now on data v0.6, method v0.4.
Still holds: The corrections log records this card unchanged at method v0.2 and again at v0.3, and its figures are recomputed from the live data when the page loads and must still match. Its stamp gives a method date rather than a version because the card was made on 14 October, the day method v0.1 was frozen.
What has moved: Nothing on this card. The calcium ranking now counts calcium at the fraction this card measured (method v0.3).
9 dairy-free foods, one serving each. Whole milk shown for reference.
| Food (one serving) | On the label | Absorbed | Tested at |
|---|---|---|---|
| Kale, cooked (85 g) | 128 mg | 52 mg | 288 mg ⚑ |
| Tempeh (85 g) | 94 mg | 35 mg | 130 mg ◇ |
| Soybeans, boiled (½ cup, 91 g) | 93 mg | 29 mg | ~98 mg ◇ |
| Bok choy, raw (85 g) | 53 mg | 27 mg | ~83 mg ◇ |
| Broccoli, raw (85 g) | 39 mg | 19 mg | ~83 mg ⚑ ◇ |
| Corn tortilla (55 g) | 45 mg | 14 mg | ~94 mg ⚑ |
| Carrot, raw (85 g) | 26 mg | 13 mg | ~38 mg, in a meal |
| Green beans, cooked (85 g) | 37 mg | 10 mg | load not reported |
| Spinach, raw (85 g) | 57 mg | 3 mg | 200 mg ⚑ ◇ |
| Whole milk, reference (250 mL) | 324 mg | 104 mg | 312 mg |
- Absorbed = calcium listed in USDA FoodData Central × the fraction absorbed in a human isotope study, at the test dose shown. Not adjusted for dose.
- ⚑ The test dose was more than twice one serving's calcium. Smaller doses are usually absorbed at a higher fraction (in one study, about 64% at the smallest doses vs about 29% at the largest, 15–500 mg: Heaney, Weaver & Fitzsimmons 1990).
- Every absorbed figure is grade A (a human study of this food); every listed figure is grade C (a database value). Ranked among the 9 reviewed foods on this card.
- Only the ends of the list are solid: kale first, spinach last. The foods in between sit within a few mg of each other and can swap with the database or study used.
- ◇ The study's abstract doesn't say how the food was prepared.
- Not on this card: almonds and sesame (we found no human isotope study of either).
Foodtopsy · audit dated 2026-10-14, on dataset v0.1 and method 2026-10-14 · sources and corrections: the receipt below · corrections · Information, not medical advice.
The same ranking, live: per serving, per 100 calories or per gram
Where each number comes from
Where every figure on the card comes from.
Listed values: USDA FoodData Central (CC0). Foundation Foods 2026-04-30 where a row exists, SR Legacy 2018-04 otherwise. Servings: Health Canada, Table of Reference Amounts for Food (V.1 vegetables 85 g; K.1 tempeh 85 g; K.2 legumes 125 mL cooked = 90.9 g at FDC's 172 g a cup; D.11 milk 250 mL = 263.1 g at FDC's 249 g a cup). Absorbed per serving = listed per serving × fraction, as published. The arm that ranks is the one whose test dose is nearest one serving's calcium, among arms of the same variant and, where known, the same preparation.
Kale, cooked
- Listed (mg/100 g) · FDC row · samples
- 150 · Foundation 326196 "Kale, frozen, cooked, boiled, drained, without salt" · 6
- Absorption study · fraction ± spread · n · population
- Heaney & Weaver 1990, Am J Clin Nutr 51:656, PMID 2321572 · 40.9% ± 10.1 (SD) · 11 · healthy premenopausal women, 20–45
- Test dose · preparation tested · access
- 288 mg (150 g serving) · blanched, frozen, cooked, puréed; eaten mid-meal · full text
- Absorbed per serving
- 52.1 mg
- Also in the receipt
- Same-study milk 32.1% at 312 mg. Heaney et al. 1993 (J Food Sci 58:1378): 52.7% at ~83 mg, n = 15, preparation not stated (would give 67.2 mg). Raw-listing figure at sign-off: 88.3 mg (retired: the study tested cooked kale)
Tempeh
- Listed (mg/100 g) · FDC row · samples
- 111 · SR 174272 "Tempeh" · 1
- Absorption study · fraction ± spread · n · population
- Haron et al. 2010, Int J Food Sci Nutr 61:125, PMID 19995131 · 36.9% ± 10.6 (SD or SEM not stated) · 20 · postmenopausal Malay women
- Test dose · preparation tested · access
- 130 mg (206 g meal) · not stated in the abstract · abstract
- Absorbed per serving
- 34.8 mg
- Also in the receipt
- Same-study milk 34.3%. Listed value rests on 1 sample
Soybeans, boiled
- Listed (mg/100 g) · FDC row · samples
- 102 · SR 174271 · 0 (calculated)
- Absorption study · fraction ± spread · n · population
- Heaney, Weaver & Fitzsimmons 1991, Am J Clin Nutr 53:745, PMID 2000830 · 31.0% ± 7.0 (SD), ordinary high-phytate soybeans · 16 · women
- Test dose · preparation tested · access
- ~98 mg · not stated in the abstract · abstract
- Absorbed per serving
- 28.7 mg
- Also in the receipt
- Same-study milk 37.7%. Low-phytate experimental line 41.4% (different variant, not ranked)
Bok choy, raw
- Listed (mg/100 g) · FDC row · samples
- 61.93 · Foundation 2685572 · 8
- Absorption study · fraction ± spread · n · population
- Heaney et al. 1993 · stems 51.9% ± 8.9, leaves 52.0% ± 7.4 (SD or SEM not stated; measured separately, the lower ranks) · 15 · women
- Test dose · preparation tested · access
- ~83 mg · not stated in the abstract · abstract
- Absorbed per serving
- 27.3 mg
- Also in the receipt
- No same-study milk (the paper cites 46.3% from earlier work). With SR Legacy's 105 mg/100 g: 46.3 mg
Broccoli, raw
- Listed (mg/100 g) · FDC row · samples
- 46 · Foundation 747447 · 8
- Absorption study · fraction ± spread · n · population
- Heaney et al. 1993 · 47.8% ± 8.9 · 15 · women
- Test dose · preparation tested · access
- ~83 mg · not stated in the abstract · abstract
- Absorbed per serving
- 18.7 mg
- Also in the receipt
- Test dose 2.1× one serving's calcium
Corn tortilla
- Listed (mg/100 g) · FDC row · samples
- 81 · SR 175036 "Tortillas, ready-to-bake or -fry, corn" · 6
- Absorption study · fraction ± spread · n · population
- Rosado et al. 2005, J Nutr 135:2578, PMID 16251614 · 32% ± 4.4 (SD), tortillas from commercial lime-treated corn flour · 9 · nonpregnant, nonlactating Mexican women
- Test dose · preparation tested · access
- ≈94 mg a meal (187.6 mg per 180 g a day, eaten as two 90 g meals with mashed potato and apple juice) · commercial lime-treated (nixtamalized) corn flour · full text
- Absorbed per serving
- 14.3 mg
- Also in the receipt
- No milk arm. Corn tortillas are made from lime-treated corn, and the listing's calcium shows it: Rosado's untreated-flour tortillas held 8.5 mg of calcium per 180 g, the lime-treated ones 187.6, so a row at 81 mg/100 g is lime-treated. CNF 3997, an independent Canadian analysis: 173 mg/100 g (30.5 mg on that listing). Home lime-treated tortillas 30% ± 2.4 at ≈163 mg; untreated flour 44% ± 3.2 of ≈4 mg (an experimental control, not a product). Test dose 2.1× one serving's calcium
Carrot, raw
- Listed (mg/100 g) · FDC row · samples
- 30.48 · Foundation 2258586 · 8
- Absorption study · fraction ± spread · n · population
- Morris et al. 2008, PNAS 105:1431, PMID 18202180 · 52.1% ± 3.2 (control carrots; SD or SEM not stated in that sentence) · 30 · young adults (15 men, 15 women)
- Test dose · preparation tested · access
- ≈38 mg from 120 g carrot, in a breakfast with ≈225 mg from calcium-fortified orange juice · sliced and frozen; cooking not stated · full text
- Absorbed per serving
- 13.5 mg
- Also in the receipt
- The study's own figure: 15.34 mg absorbed per 100 g of its control carrots
Green beans, cooked
- Listed (mg/100 g) · FDC row · samples
- 44 · SR 169141 "Beans, snap, green, cooked, boiled, drained, without salt" · 27
- Absorption study · fraction ± spread · n · population
- Grusak & Abrams, "Bioavailability of calcium from common vegetables assessed in teenagers", USDA-ARS publication record 73011 · 28% · 13 · teenagers (7 girls, 6 boys)
- Test dose · preparation tested · access
- not reported · cooked, puréed, frozen; fed with milk during a two-week metabolic-unit stay; bioavailability from a compartmental model · record
- Absorbed per serving
- 10.5 mg
- Also in the receipt
- "comparable to that of milk calcium", no number given
Spinach, raw
- Listed (mg/100 g) · FDC row · samples
- 66.64 · Foundation 1999633 "Spinach, mature" · 8
- Absorption study · fraction ± spread · n · population
- Heaney, Weaver & Recker 1988, Am J Clin Nutr 47:707, PMID 3354496 · 5.1% · 13 · adults
- Test dose · preparation tested · access
- 200 mg · not stated in the abstract · abstract
- Absorbed per serving
- 2.9 mg
- Also in the receipt
- Same-study milk 27.6%. Weaver & Heaney 1991 (PMID 1760767): 2.9% at 200–300 mg, n = 14 (1.6 mg). Adolescents: ~3%. Test dose 3.5× one serving's calcium
Whole milk (reference)
- Listed (mg/100 g) · FDC row · samples
- 123 · Foundation 746782 · 11
- Absorption study · fraction ± spread · n · population
- Heaney & Weaver 1990 (the kale study's own milk arm) · 32.1% ± 8.9 (SD) · 11 · healthy premenopausal women, 20–45
- Test dose · preparation tested · access
- 312 mg · fluid milk, eaten mid-meal · full text
- Absorbed per serving
- 103.9 mg
- Also in the receipt
- Unranked. Within that one study, kale's calcium was absorbed slightly better than milk's (40.9% vs 32.1%; the authors call the difference probably of little practical importance). Recker et al. 1988 (PMID 3337043, whole milk, 250 mg, fasting): the abstract gives 21–26% for all six sources it tested (five milk products and calcium carbonate); a 2021 review reports 26.7% for whole milk (86.4 mg), which we couldn't check against the paper
Why some rows are cooked and others raw: each row's listing matches the preparation the absorption study tested when the full text or study record says so. Where the abstract is silent, the raw listing is used and the row carries ◇.
Dose and absorption: Heaney, Weaver & Fitzsimmons 1990, J Bone Miner Res 5:1135, PMID 2270776: fractional absorption fell with the logarithm of the load; 64.0% at the lowest loads, 28.6% at the highest (15–500 mg, healthy adult women, with meals).
Not measured, so not ranked: the "21.2%" for almonds and "20.8%" for sesame that circulate online were derived from rat ratios applied to human milk absorption; the brassica figures in the same table (turnip greens, cauliflower and others) were predicted from kale and an equation (Weaver & Plawecki 1994, Am J Clin Nutr 59:1238S, Table 2, footnote 3).
The tortilla: lime treatment (nixtamalization) is what puts calcium in a corn tortilla, and it is how corn tortillas are made. In Rosado et al. 2005 (J Nutr 135:2578), lime-treated tortillas held 187.6 mg of calcium per 180 g and untreated ones 8.5 mg; women absorbed about 60 to 98 mg a day from the lime-treated ones against about 4 mg from the untreated. The USDA row (81 mg/100 g) and the Canadian Nutrient File's own analysis (173 mg/100 g) don't name the process, but calcium at those levels only comes from it, so the tortilla is on the card on the USDA listing.