Table 3.

Dietary factors supposed to inhibit bioavailability of Mg²⁺.

Studies are sorted by dietary factors. Mg²⁺ intake is consistently indicated in mg. Specifications in mmol were converted to mg.

Species	Design	Duration	Dietary Factor Investigated	Diet/ Doses	Target Parameter For Mg2+ Bioavailability	Core Result	Refs.
9 Healthy Adults	Cross-over (1 day wash-out), stable isotopes 25Mg2+ and 26Mg2+	Single test meals	Oxalic acid (OA)	2 diets: 1) 300 g spinach (6.6 mmol OA; 122 mg Mg2+ incl. 17.0 mg 25Mg2+) 2) 300 g kale (0.1 mmol OA; 117 mg Mg2+ incl. 29.2 mg 26Mg2+)	Mg2+ excretion in faeces	OA reduce Mg2+ absorption	[32]
Male Wister Rats	Parallel group, control-diet	8 days	OA	6 diets: 1) Mg2+-deficient diet (control, 0.3 mg Mg2+) 2) raw powdered spinach (R-sp + 34.5 mg Mg2+) 3) boiled powdered spinach (B-sp + 34.8 mg Mg2+) 4) fried powdered spinach (F-sp + 35.9 mg Mg2+) 5) control diet with OA (Ox-C + 33.6 mg Mg2+) 6) control diet + 31.1 mg Mg2+	Mg2+ excretion in faeces and urine	OA reduce Mg2+ absorption Rate of absorbed Mg2+: control 88.9%, R-sp 80.2%, B-sp 88.4%, F-sp 90.4%, Ox-C 88.1%, + Mg2+ 87.7%	[96]
20 Healthy Adults	Cross-over (1 day wash-out), placebo-controlled, stable isotopes 25Mg2+ and 26Mg2+	Single test meals	Phytic acid (PA)	2 diets with 200 g wheat bread: 1) 0.75 mmol PA (+ 88.5 mg Mg2+ incl. 17.0 mg 25Mg2+) 2) 1.49 mmol PA (+ 88.5 mg Mg2+ incl. 26.7 mg 26Mg2+)	Mg2+ excretion in faeces	PA reduce Mg2+ absorption, PA inhibiting effect was dose dependent	[33]
78 Male Sprague-Dawley Rats	Randomized, control-diet	1, 3, or 5 weeks	Potato starch (PS) with esterified phosphorus (EP)	4 diets: 1) EP-free control diet (+ 11.0 mg Mg2+) 2) 600 g Cornstarch (+ 8.0 mg Mg2+) 3) 600 g Benimaru PS (+ 8.3 mg Mg2+) 4) 600 g Konafubuki PS (+ 9.3 mg Mg2+)	Mg2+ excretion in faeces	PS-EP reduce Mg2+ absorption	[98]
40 Premenopausal and Post Menopausal Women	Randomized, placebo-controlled, single-blind, cross-over (2 weeks wash-out), stable isotope 26Mg2+	2 weeks + single test meals for Mg2+ absorption	Wheat dextrin (WD)	Cookies with 15.0 g WD/d or without (placebo) 120 mg Mg2+ incl. 29.2 mg 26Mg2+	Mg2+ excretion in urine	No significant differences	[34]
26 Adolescent Girls	Randomized, placebo-controlled, double-blind, parallel-group	2 weeks	Calcium	3 diets with basal Mg2+ intake of 176 mg Mg2+: 1) Placebo diet 2) low calcium (667 mg/d) 3) high calcium (1,667 mg/d)	Mg2+ excretion in urine and faeces	No significant differences	[95]
5 Adolescent Girls	Randomized, cross-over (5 weeks wash-out), stable isotopes 25Mg2+ and 26Mg2+	2 weeks	Calcium	2 diets (each + 40.0 mg 26Mg2+ oral + 20.0 mg 25Mg2+ intravenously): 1) low calcium (800 mg/d) + 305±30.0 mg Mg2+/d 2) high calcium (1,800 mg/d) + 286±9.0 mg Mg2+/d	Mg2+ excretion in urine and faeces	No significant differences	[35]