Moderately Low Magnesium Intake Impairs Growth of Lean Body Mass in Obese-Prone and Obese-Resistant Rats Fed a High-Energy Diet.

The physical and biochemical changes resulting from moderately low magnesium (Mg) intake are not fully understood. Obesity and associated co-morbidities affect Mg metabolism and may exacerbate Mg deficiency and physiological effects. Male rats selectively bred for diet-induced obesity (OP, obese-prone) or resistance (OR, obese-resistant) were fed a high-fat, high-energy diet containing moderately low (LMg, 0.116 ± 0.001 g/kg) or normal (NMg, 0.516 ± 0.007 g/kg) Mg for 13 weeks. The growth, body composition, mineral homeostasis, bone development, and glucose metabolism of the rats were examined. OP and OR rats showed differences (p < 0.05) in many physical and biochemical measures regardless of diet. OP and OR rats fed the LMg diet had decreased body weight, lean body mass, decreased femoral size (width, weight, and volume), and serum Mg and potassium concentrations compared to rats fed the NMg diet. The LMg diet increased serum calcium (Ca) concentration in both rat strains with a concomitant decrease in serum parathyroid hormone concentration only in the OR strain. In the femur, Mg concentration was reduced, whereas concentrations of Ca and sodium were increased in both strains fed the LMg diet. Plasma glucose and insulin concentrations in an oral glucose tolerance test were similar in rats fed the LMg or NMg diets. These results show that a moderately low Mg diet impairs the growth of lean body mass and alters femoral geometry and mineral metabolism in OP and OR rats fed a high-energy diet.

l-Lysine supplementation does not affect the bioavailability of copper or iron in rats.

l-lysine (Lys) is an essential amino acid that is added to foods and dietary supplements. Lys may interact with mineral nutrients and affect their metabolism. This study examined the effect of dietary Lys supplementation on the bioavailability of copper (Cu) and iron (Fe). Weanling male Sprague-Dawley rats were fed one of five diets (20% casein) for 4 weeks containing normal Cu and Fe (control) or low Cu or Fe without (LCu, LFe) or with (LCu+Lys, LFe+Lys) addition of 1.5% Lys. Final body weights, body weight gains and food consumption of the rats did not differ (P≥0.05) among diet groups. Rats fed the low Cu or Fe diets showed changes in nutritional biomarkers compared to control rats, demonstrating reduced Cu and Fe status, respectively. Hematological parameters, serum ceruloplasmin activity and Cu and Fe concentrations in serum, liver, kidney and intestinal mucosa were unaffected (P≥0.05) by Lys supplementation. These results indicate that in the context of an adequate protein diet, Lys supplementation at a relatively high level does not affect Cu or Fe bioavailability in rats.