The best plant-based sources of calcium Original paper

In this in vitro study, the plant-based foods estimated to provide the most bioaccessible (absorbable) calcium per serving were kale, millet porridge, fortified white bread, kidney beans, and black chickpeas.

The amount of bioaccessible (absorbable) calcium provided by various plant-based foods, with skim cow’s milk serving as a reference (because it is well established as a good source of calcium).

This study was conducted without human participants.

Instead, 26 foods — specifically 4 types of grains, 6 types of legumes, 4 types of vegetables, 4 plant-based milk alternatives, 4 types of dried fruit, tahini, and skim milk — were selected and analyzed.

Aside from the grains and skim milk, all foods were selected because they were recommended sources of calcium for a vegan diet on the UK National Health Service (NHS) website.^[1]

This in vitro study analyzed the calcium content, calcium bioavailability (percent absorption), and bioaccessible calcium provided by various foods.

Calcium content was measured using a validated analytical method. Calcium bioavailability was estimated by measuring the percentage of extractable calcium after a process designed to replicate the digestive process. These data were used to determine the amount of bioaccessible calcium provided by each food, expressed as milligrams (mg) of absorbable calcium provided per serving.

The best source of calcium was kale, which provided 5 times more bioaccessible calcium per serving (328 mg of calcium per 80 grams) than skim milk (72.4 mg of calcium per 200 mL). The next best sources of bioaccessible calcium were millet porridge (56.3 mg of calcium per 160 grams), fortified white bread (51.8 mg of calcium per 94 grams), black chickpeas (39.3 mg of calcium per 150 grams), and kidney beans (39.3 mg of calcium per 150 grams).

The worst sources of bioaccessible calcium were spinach (0.21 mg of calcium per 80 grams), tahini (0.29 mg of calcium per 5 grams), oat porridge (2.42 mg of calcium per 160 grams), and soy milk (3.24 mg of calcium per 200 mL). Dried fruits (apricots, figs, prunes, and raisins) were also poor sources of calcium, with bioaccessibility ranging from 5.5 to 8.6 mg of calcium per 30 grams for foods in this group.

It’s worth emphasizing that this study did not measure calcium absorption in actual humans. The study attempted to replicate various stages of digestion by exposing the foods to saliva, stomach acid, digestive enzymes, and bile, often at specific pH levels and temperatures. However, this process may not perfectly represent what actually happens inside the human body.

As an example, the study estimated that the calcium plant-based milk substitutes (soy milk, rice milk, almond milk, and oat milk) fortified with calcium diphosphate/triphosphate were only about 3.22% to 5.16% bioavailable (compared to 29.9% for skim milk). Yet this estimate appears far lower than in studies involving humans, with one study in 20 women finding that soy milk fortified with tricalcium phosphate was 18.1% bioavailable.^[2] As such, the values provided by this study (especially relating to the plant-based milk substitutes) should be viewed with caution.