Wai
10-18-2002
06:40 AM | quote:
According to fitday I'm only getting about 50-60% of my RDA for zinc/iron.
The thing with minerals / metals is that the body can very effectively adapt the absorption rate to a 10-fold extend. If your diet contains relatively little of a certain mineral, the body simply increases the absorption rate. If your diet contains high levels of that mineral, then your body lowers the absorption rate. In that sense, RDAs are absolutely useless.
Why does the body lower the absorption rate of metals such as zinc and iron if your diet contains high levels of these metals?
Because these metals have pro-oxidative properties; your body simply wants to prevent an increase in the influence of pro-oxidants. your body wants to maintain the proper balance between pro- and anti-oxidants.
Why are RDAs given for metals anyway?
Because we have the tendency to think that, regarding micro-nutrients, 'more is always better'. But, as with macro-nutrients (protein, sugars, fats), this is not true for micro-nutrients either.
Elevated levels of metals like iron, copper, cobalt, manganese and zinc is pro-oxidative (1), damaging nutrients, arteries (2) messenger-substances, cell-DNA (3) and enzymes (4), increases hart attack risk, and can cause diabetes (5), colon cancer (6) Parkinson's disease (7) and infertility. (8)
quote:
(1) Horwitt, M.K., Do the metals in vitamin-mineral supplements produce undesirable oxidations ? Am. J. Clin. Nutr. 1997 / 65 (5) / 1571. , Kehrer, J.P., Free radicals as mediators of tissue injury and disease. Crit.Reviews Toxicol. 1993 / 23 / 21-48. , Yu, B.P., Cellular defenses against damage from reactive oxygen species. Physiol. Reviews 1994 / 74 / 139-161. , Halliwell, B. and M.C. Gutteridge, Role of free radicals and catalytic metal ions in human disease : An overview. Methods Enzymol. 1990 / 186 / 1-85.
(2) Lee, T.S. et al, Iron-deficient diet reduces atherosclerosis lesions in ApoE-deficient mice Circuation 1999 / 99 (9) / 1222-1229. , Patel, R.P. et al, Formation of oxysterols during oxidation of low density lipoprotein by peroxynitrite, myoglobine, and copper. J. Lipid. Res. 1996 / 37 (11) / 2361-2371. , Dzeletovic, S. et al, Time course of oxysterol formation during in vitro oxidation of low density lipoprotein. Chem. Phys. Lipids 1995 / 78 (2) / 119-128. , Herbert, V. et al, Iron worsenes high cholesterol-related coronary artery disease. Am. J. Clin. Nutr. 1994 / 60 (2) / 299-300.
(3) Oikawa, S. et al, Distinct mechanisms of site-specific DNA damage induced by endogenous reductants in the presence of iron (III) and copper (II). Biochem. Biophys. Acta 1998 / 1399 (1) / 19-30.
(4) Sok, D.E., Oxidative inactivation of brain alkaline phosphatase responsible for hydrolysis of phosphocholine. J. Neurochem. 1999 / 72 (1) / 355-362.
(5) Burke, W. et al, Hemachromatosis : genetics helps to define a multifactorial disease. Clin. Genet. 1998 / 54 (1) / 1-9. , Crawford, R.D., Proposed role for a combination of citric acid and ascorbic acid in the production of dietary iron overload : a fundamental cause of disease Bichem. Mol. Med. 1995 / 54 (1) / 1-11. , Britton, R.S. et al, Pathophysiology of irontoxicity. Adv. Exp. Med. Biol. 1994 / 356 / 239-253. , Phatak, P.D. et al, Management of hereditary hemachromotosis. Blood Rev. 1994 / 8 (4) / 193-198.
(6) Sawa, T. et al, Lipid peroxyl radicals from oxidized oils and heme-iron :implication of a high fat diet in colon carcinogenesis. Cancer Epidemiol. Biomarkers Rev. 1998 / 7 (11) / 1007-1012.
(7) Jellinger, K.A., The role of iron in neurodegeneration : prospects for pharmacotherapy of Parkinson's disease. Drugs. Aging. 1999 / 14 (2) / 115-140. , Spencer, J.P. et al, Conjugates of catecholamines with cysteine and GSH in Parkinson's disease : possible mechanisms of formation involving reactive oxygen species. J. Neurochem. 1998 / 71 (5) / 2112-2122. , Snyder, R.D. et al, Enhancement of cytotoxicity and and clastogenicity of L-dopa and dopamine by manganese and copper. Mutat. Res. 1998 / 405 (1) / 1-8. , Vescovi, A. et al, Interactions of manganes with human brain glutathione-S-transferase. Toxicology 1989 / 57 (2) / 183-191.
(8) Olsen, P.A. et al, Effects of supplementation of organic and inorganic combinations of copper, cobalt, manganese, and zinc above nutrient requirement levels on postpartum two-year-old cows. J. Anim. Sci. 1999 / 77 (3) / 522-532.
If you think that you need more iron or zinc anyway, you can eat more foods that contain high levels of these metals, such as egg yolks:
ZINC, in mg / 100 gram
4.3 beef; for comparison
4.0 Brazil nuts
3.8 egg yolk
2.7 walnuts
1.9 hazelnuts
0.8 dried figs
0.8 salmon
0.8 coconut
0.7 granadilla
IRON, in mg / 100 gram
7.2 egg yolk
3.3 dried figs
3.8 hazelnuts
3.4 Brazil nuts
2.3 coconut
2.2 beef; for comparison
1.9 rambutan
1.9 dried dates
1.8 olives
1.3 granadilla
1.3 carissa
1.0 salmon
1.0 tuna |
