Zinc's Role in Rat Preference for a Low-Fat Diet in a Two-Choice Diet Program of Low- and High-Fat Diets

Abstract

SummaryTo investigate the change in preference for a low-fat diet (LFD) and a high-fat diet (HFD) under disorders induced by a zinc (Zn)-deficiency, two groups of 4-wk-old male rats were fed a two-choice diet of Zn-deficient (ZnD; 0.75 mg/kg) and Zn-adequate (ZnA; 30.75 mg/kg) LFD and HFD. After 21 d, 10 rats in each of the two groups were sacrificed. The remaining ZnD rats were switched to ZnA diets for 7 d. Intakes of the LFD and the HFD were measured to determine the diet preferences of the ZnD, the ZnA and the Zn-recovered groups. Energy intake of the ZnD group was significantly lower than that of the ZnA group and showed cyclical 3-to 4-d patterns of decrease. In the ZnD group, although the LFD intake decreased parallel to the reduction in the energy intake, the HFD intake did not show the cyclical pattern of decrease. The reduced intake of the LFD in the ZnD rats was accompanied by a low carbohydrate intake and a low plasma insulin concentration. When the ZnD group recovered sufficient amounts of Zn, the energy intake was restored to normal levels and the difference in the LFD intake and the plasma insulin concentration disappeared between the ZnD and the ZnA groups. It was supposed that the specific change in the LFD intake patterns during development and recovery from Zn-deficiency might be related to Znmediated changes in impaired synthesis and the release of insulin from the pancreas. Key Words zinc-deficiency, self-selection, preference for a low-fat diet, two-choice diet program, high-fat diet Zinc (Zn) is essential for animals and humans, and is required for many physiological functions. A Zn-deficiency in both animals and humans causes anorexia, a taste disorder, a poor appetite, impaired growth and dermatitis ( 1-3 ). Within 3 to 5 d after giving rats a Zndeficient (ZnD) diet, food intake is suppressed ( 3,4 ). This decrease in food intake is the first sign of Zn-deficiency, followed by other symptoms associated with Zndeficiency ( 3 ). Therefore, Zn may play an important role in the regulation of food intake.From a whole-body perspective, ZnD rats have significantly reduced body weight and carcass fat, and lower circulating leptin and insulin concentrations that play key roles in energy nutrient metabolism compared to the Zn-adequate (ZnA) rats ( 4-7 ). Leptin is produced by adipose tissue and has potent effects on body weight and food intake regulation. Another adiposity signal is insulin, which is the controller of blood glucose levels, and chronically high levels of insulin consequently lead to obesity ( 8 ). Arora and Anubhuti reported that leptin and insulin are ideal candidates for lipogenic function because their levels are closely related to adiposity, and their central administration decreases food intake ( 9 ). However, feeding is a complex behavior and the mechanisms by which Zn-deficiency induces anorexia are unclear. Zn-deficiency results in a reduction of food intake, suggesting that Zn status may affect the complex mechanisms underlying normal food intake.In a previous paper, we re...

Zinc‐containing yeast extract promotes nonrapid eye movement sleep in mice

“…In this experiment, 15 min after i.p. injection, radiolabeled zinc can already be detected in the CSF, with further increase until 6 h. Zinc concentration then start to decrease and become undetectable after 24 h. At baseline level, free zinc Zn 2+ concentration in the CSF is extremely low, around 5–25 nM compared to 46 ± 6 μM in the plasma , such quick change of Zn 2+ concentration in the CSF could be the responsible for sleep induction observed in our study.…”