Magnesium absorption in human subjects from leafy vegetables, intrinsically labeled with stable 26Mg

Collards, turnip greens, leaf lettuce, and spinach, grown in nutrient solution so that their Mg content was 80 to 90% 26Mg, were tested in ambulant male volunteers stabilized on a constant metabolic diet. The freeze-dried vegetables were incorporated in bran muffins in which the vegetables replaced part of the bran. Bran muffins without vegetables were consumed for breakfast each day. They were also used as a standard test meal to which the vegetable muffins were compared. All subjects participated in three consecutive isotope absorption tests: one of the standard test meal and two of the vegetables. The standard test was carried out after at least 30 days on the controlled diet. Subsequent tests of vegetables followed at 4-wk intervals. Each test meal contained 30 microCi 28MgCl2 and 50 mg stable 26Mg, the latter either as the intrinsic label of a test vegetable or as 26MgCl2 in solution taken with the standard bran muffins. Net absorption of both isotopes was measured to establish exchangeability and to determine relative Mg absorption from the vegetables. Exchangeability was 90% or higher from all meals tested. Relative Mg absorption was highest from collards and least from the standard test meal. Net absorption values ranged from 40 to 60%.