Zinc, copper and magnesium absorption from a fibre-rich diet

Zinc, copper and magnesium absorption and retention from a high-fibre and high-phytate diet of conventional foods were investigated in 8 healthy subjects. Fractional absorption of the three minerals was estimated from fecal monitoring of zinc, copper and magnesium stable isotopes added to one day's diet. In addition, apparent absorption, retention and endogenous losses were estimated for the respective minerals based on fecal and urinary excretion over the last 16 days of 21 days constant intake. The diet contained 1 mmol phytic acid, 29 g dietary fiber, 140 mumol zinc, 13 mumol copper, and 9 mmol magnesium per 10 MJ. The absorption of zinc, copper and magnesium was 29 +/- 12% (x +/- SD) (48 +/- 20 mumol), 44 +/- 7% (8 +/- 1 mumol) and 46 +/- 6% (5 +/- 1 mmol), respectively. The retained amounts of minerals were -7 +/- 19 mumol, -5 +/- 4 mumol, and -3 +/- 1 mmol, respectively and the estimated endogenous intestinal losses were 40 +/- 20 mumol, 12 +/- 4 mumol and 3 +/- 1 mmol, respectively. In conclusion, the fractional absorption of zinc, copper and magnesium from the fibre-rich diet was not sufficient to cover intestinal and urinary losses of these elements, resulting in negative balances.