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United States Department of Agriculture

Agricultural Research Service

Research Project: MINERAL INTAKES FOR OPTIMAL BONE DEVELOPMENT AND HEALTH Title: Dietary Fatty Acid Composition Alters Magnesium Metabolism, Distribution, and Marginal Deficiency Response in Rats

Author
item NIELSEN, FORREST

Submitted to: Magnesium Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 10, 2009
Publication Date: December 20, 2009
Repository URL: http://handle.nal.usda.gov/10113/46629
Citation: Nielsen, F.H. 2009. Dietary Fatty Acid Composition Alters Magnesium Metabolism, Distribution, and Marginal Deficiency Response in Rats. Magnesium Research. 22(4):280-288.

Interpretive Summary: Based on dietary intake recommendations, magnesium deficiency commonly occurs throughout the world. However, widespread health problems caused by a dietary magnesium deficiency have not been identified. This discrepancy may be the result of other dietary factors, and/or the length of deprivation, making the response to marginal magnesium deficiency more or less severe. A diet high in polyunsaturated omega-3 fatty acids (high in fish oil) relative to polyunsaturated omega-6 fatty acids (high in corn oil) has been found to decrease oxidative stress and chronic inflammation, which are common components of chronic diseases such as ischemic heart disease and osteoporosis. Magnesium deprivation has been associated with oxidative stress and chronic inflammation. Thus, an experiment was performed to determine whether the omega-6/omega-3 fatty acid composition of the diet affected the response of rats to marginal magnesium deficiency, and whether the effect was dependent upon the length of deprivation. Dietary fatty acid composition influenced the effect of marginal magnesium deficiency on magnesium metabolism, distribution and oxidative stress indicators. Fish oil, but not corn oil, significantly decreased the urinary magnesium excretion and increased kidney magnesium concentration. Femur magnesium was significantly decreased by marginal magnesium deficiency in rats fed fish oil, but not in rats fed corn oil, and liver magnesium was decreased by fish oil. Marginal magnesium deficiency increased two Indicators of oxidative stress in blood of rats fed corn oil but not in rats fed fish oil. Urinary prostaglandin E2, an indicator of inflammatory stress, was significantly decreased by marginal magnesium deficiency after 8 weeks, but not at 12 weeks, of magnesium deprivation. A marked increase between weeks 8 and 12 in magnesium-deficient rats fed fish oil caused this change in significance. The findings support the contention that the response to marginal magnesium deprivation depends upon other dietary factors, including the fatty acid composition of the diet. The findings also suggest that dietary factors affecting oxidative stress could affect the response to marginal magnesium deprivation. In addition, a response to a dietary change that takes time to develop, such as the response to an increase in omega-3 fatty acids, may result in signs of marginal magnesium deficiency being very different over time, or a low magnesium status may modify the response to the dietary change. These modifying factors may be a major reason for the difficulty in identifying signs of marginal magnesium deficiency in humans, and in definitively concluding that inadequate dietary magnesium significantly contributes to the occurrence of chronic diseases such as ischemic heart disease and osteoporosis.

Technical Abstract: Based on dietary intake recommendations, magnesium deficiency commonly occurs throughout the world. However, widespread pathological conditions induced by dietary magnesium deficiency have not been identified. This discrepancy may be caused by other dietary factors ameliorating or exacerbating the response to a marginal magnesium deficiency and/or the length of the deficiency. Thus, an experiment was performed to determine whether the n-6/n-3 fatty acid composition of the diet affects the response to marginal magnesium deprivation, and whether the effect was dependent upon the length of deprivation. Weanling female rats were fed diets containing 250 mg/kg magnesium in a factorial arrangement with dietary variables of supplemental magnesium at 0 or 250 mg/kg and fat sources of 75 g/kg safflower oil or 65 g/kg fish (menhaden) oil plus 10 g/kg linoleic acid. After 8 and 12 weeks on their respective diets, each rat was placed in a metabolic cage for a 16-hour collection of urine. After 13 weeks, the rats were anesthetized with ether for the collection of plasma and organs. Marginal magnesium deficiency was confirmed by decreased urinary excretion and femur, tibia and vertebrae concentrations of magnesium. Dietary oil influenced the effect of marginal magnesium deficiency on magnesium metabolism, distribution and oxidative stress indicators. Fish oil, but not corn oil, significantly decreased urinary magnesium excretion and increased kidney magnesium concentration. Femur magnesium was significantly decreased by marginal magnesium deficiency in rats fed fish oil but not in rats fed corn oil, and liver magnesium concentration was decreased by fish oil. Marginal magnesium deficiency increased plasma extracellular superoxide dismutase and cysteine (component of glutathione) in rats fed corn oil but not in rats fed fish oil. Urinary prostaglandin E2 excretion was significantly decreased by marginal magnesium deficiency at 8 weeks, but not at 12 weeks; a marked increase between weeks 8 and 12 in marginally magnesium-deficient rats fed fish oil caused this change in significance. The findings show that the dietary fatty acid composition affects the response of rats to marginal magnesium deprivation. The findings also indicate that dietary or physiological factors affecting oxidative stress could affect the response to marginal magnesium deficiency, and that a response to a dietary change that takes time to develop, such as an increase in dietary n-3 fatty acids, may result in signs of marginal deficiency being different over time.

Last Modified: 9/10/2014
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