Interaction Between Marginal Zinc and High Fat Supply on Lipid Metabolism and Growth of Weanling Rats

Abstract

The impact of a moderate Zn deficiency on growth and plasma and liver lipids was investigated in two 4-week experiments with male weanling rats fed fat-enriched diets. Semisynthetic, approximately isocaloric diets containing 3% soybean oil were supplemented with either 7 or 100 mg Zn/kg diet and with 22% beef tallow (BT) or sunflower oil (SF). In Experiment 1, which compared the dietary fat level and the fat source in a factorial design of treatments, all diets were fed ad libitum to 6 × 8 animals, whereas intake of the high-Zn BT and SF diets was restricted in Experiment 2 (5 × 6 rats) to the level of intake of the respective low-Zn diets. The low-Zn SF diet consistently depressed food intake and final live weights of the animals to a greater extent than the other low-Zn diets, while intake and growth were comparable among the animals fed the high-Zn diets. The marginal Zn deficit per se did not alter plasma triglyceride and cholesterol concentrations nor hepatic concentrations of triglyceride, cholesterol and phospholipids. The fatty acid pattern of liver phospholipids did not indicate that chain elongation and desaturation of fatty acids was impaired by a lack of zinc. It was concluded that dietary energy and fat intake, and fat source have a greater effect on plasma and liver lipids than a moderate Zn deficiency. Marginally Zn-deficient diets enriched with sunflower oil as a major energy source cause a greater growth retardation than diets rich in carbohydrates or beef tallow.

A Moderate Zinc Deficiency Does Not Impair Gene Expression of PPARα, PPARγ, and Mitochondrial Enoyl-CoA Delta Isomerase in the Liver of Growing Rats

“…Plasma and femur Zn concentrations in the groups fed the HZ-SF diet either free choice or in restricted amounts were comparable (Table 2). This agrees with former studies showing that plasma or serum Zn concentrations are not altered when Zn-adequate diets are fed in restricted amounts as compared with ad libitum feeding 22,30–33. Finally, growth retardation because of an alimentary Zn deficit cannot be attributed to a loss of appetite as the primary cause.…”

“…It has already been shown in 1970 that increasing the food intake of Zn-depleted young rats by force-feeding does not alleviate the growth arrest but instead quickly elicits severe signs of ill health and morbidity of the animals 34. Taken together, the evidence of the present study indicates a poorer Zn status of the rats fed the LZ-SF diet compared with those fed the LZ-CB diet despite comparable liver Zn concentrations, in agreement with previous studies 22,35. The underlying mechanism for this effect of fat source on Zn status awaits further research.…”

“…In agreement with such a nutritional state, the livers of young rats force-fed Zn-deficient diets displayed markedly higher activities of lipogenic enzymes63 and increased triglyceride concentrations 58. In contrast, triglyceride concentrations in the liver of young rats offered Zn-deficient diets for voluntary consumption were not higher than in the liver of Zn-supplemented control animals fed ad libitum or restrictedly 22,58. In line with these former studies, hepatic TAG concentrations did not differ between the rats fed the LZ and HZ diets in our experiment (Fig.…”

“…Hence, it is reasonable to assume that hepatic de novo fatty acid synthesis was greatly depressed in our experiment. In support, in weanling rats fed very similar high-fat, low-carbohydrate diets, the hepatic activity of glucose-6- phosphate dehydrogenase, which belongs to the lipogenic enzyme family and closely correlates with the rate of fatty acid synthesis in the liver,57 was greatly reduced as compared with animals fed a low-fat, high-carbohydrate diet 22. Third, the most decisive difference in the experimental protocols concerns the feeding regimen.…”

“…Hepatic triglyceride concentration was determined as described previously 22. Briefly, total lipids were extracted in hexane:isopropanol and analyzed for triglycerides by a colorimetric assay kit (Roche Diagnostics, Mannheim, Germany).…”