Is spinach a good source of magnesium?

Japanese researchers evaluated spinach’s magnesium bioavailability in rats in a study published in 1995 (1). Their conclusions were that spinach was a "one of the most promising" sources of magnesium and that oxalic acid in spinach after cooking (boil or fried) would not affect magnesium bioavailability.

Looking at their data, though, cooking did affect calcium absorption and, of course, oxalic acid had additional effects.

The researchers had divided rats into six groups, which led to this data:

• Mg-deficient diet
  o Serum magnesium decrease
  o Ca absorption 87.0%
  o Increase of calcium and phosphorus in liver and kidneys
  o Especially large calcium accumulation in kidneys
• Mg-deficient diet supplemented with raw powdered spinach
  o Mg absorption 88.9%
  o Ca absorption 84.1%
  o Large calcium accumulation in kidneys
  o Significantly higher liver and kidney Mg and phosphorus
• Mg-deficient diet with boiled powdered spinach
  o Mg absorption 88.4%
  o Ca absorption 57.3%
  o Large calcium accumulation in kidneys
  o Significantly higher liver and kidney Mg and phosphorus
• Mg-deficient diet with powdered fried spinach
  o Mg absorption 90.4%
  o Ca absorption 66.2%
  o Large calcium accumulation in kidneys
  o Significantly higher liver and kidney Mg and phosphorus
• Control diet with supplemented oxalic acid
  o Mg absorption 88.1%
  o Ca absorption 53.3%
  o Large calcium accumulation in kidneys
  o Significant decrease in weight
• Control diet
  o Mg absorption 87.7%
  o Ca absorption 83.5%o
  o Significant increase in weight gain in comparison to other groups
  

Reference List

1. Kikunaga S, Ishii H, Takahashi M. The bioavailability of magnesium in spinach and the effect of oxalic acid on magnesium utilization examined in diets of magnesium-deficient rats. J Nutr Sci Vitaminol (Tokyo) 1995;41:671-85.