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Food · Grains & Legumes · Legumes
food source · 2
→Iron
The iron in black beans is non-heme iron that phytate holds back; a food rich in vitamin C in the same meal clearly helps it get absorbed, by the same mechanism as in lentils.
Mechanism · The same door as lentils
Like the iron in lentils, the iron in black beans is non-heme iron: phytate locks it up, and vitamin C in the same meal reduces it to ferrous iron in the gut and escorts it in. Tomato or green pepper in the soup helps the iron in this meal's beans; it does not build up a body that absorbs iron better later.
Numbers · The iron needs help from the sides
Cooked black beans have about 2.1 mg of iron per 100 g. The beans themselves have almost no vitamin C, so it has to come from the side dishes. Dry beans should be soaked well and cooked until completely soft; changing the water after soaking removes some of the gas-producing oligosaccharides and helps lower the phytate too.
Black beans carry a share of magnesium: about 70 mg per 100 g cooked, roughly 17–22% of an adult's daily need. Magnesium takes part in energy production and in signaling between nerves and muscles.
Mechanism · ATP depends on magnesium
Magnesium takes part in more than 300 enzyme reactions, including making ATP and passing signals between nerves and muscles. ATP has to bind magnesium before enzymes recognize it. Black beans pack magnesium, plant iron and folate into one seed.
Numbers · The magnesium in a serving
Cooked black beans have about 70 mg of magnesium per 100 g, roughly 17–22% of the adult daily need of 320–420 mg, along with about 149 µg DFE of folate and about 355 mg of potassium. Their protein is still incomplete and is best paired with grains.