## 4 Discussion  
A high-protein diet has been proposed to promote weight loss and has been one of the most popular weight-loss strategies [24], but its effect on lipid metabolism still remains unclear. High-protein diets, compared with high-carbohydrate or high-fat diets, provide a higher level of satiety for a longer period of time, which could lead to long-term reduced energy intake [25; 26]. Indeed, in our study, the diet intake in the LCHP\({}_{\text{ch}}\) group was lower, but statistical significance was observed only in week 6. Meanwhile, the body weight remained unchanged, despite decreasing tendency from the same week. [PERSON] et al. [2] noticed hepatic enlargement (under conditions of 50% protein in the diet). We did not observe significant changes in the liver weight, despite an increasing tendency in the LCHP\({}_{\text{ch}}\) group. When considering serum lipid profile, it was observed that LCHP\({}_{\text{ch}}\) diet intake caused significant enhancement of LDL + VLDL concentration. In addition to LDL + VLDL, data for TCH, HDL and TAG make up the primary lipid panel for the diagnosis of hyperlipidemia and enable the estimation of cardiovascular (CV) risk [27]. Atherogenic index (AI) is an indicator of the magnitude of atherosclerosis [21]. The higher the AI, the more elevated the potential occurrence of atherosclerosis and prevalence of CV disease. [PERSON] et al. [21] showed that a lipid-rich diet after 30 days increased AI significantly (\(p<0.01\)) from 0.61 to 5.7. In our study, AI was also enhanced as a  
Figure 5: Histological appearance of liver of: (a) AIN\({}_{\text{ch}}\), (b) WD\({}_{\text{ch}}\) (c) LCHP\({}_{\text{ch}}\) rats (200\(\times\)) stained with ORO. Figure 6: ORO staining/tissue area (%) of liver of rats after 8 weeks of feeding: AIN\({}_{\text{ch}}\), WD\({}_{\text{ch}}\) or LCHP\({}_{\text{ch}}\) diets, enriched with 1% cholesterol. The means marked with letters a and b are significantly different (\(p<0.05\)). consequence of feeding animals not only a WD\({}_{\rm ch}\) diet (as expected), but also the LCHP\({}_{\rm ch}\) diet. Therefore, the risk of CV disease was increased. Another biomarker for CV risk is the ratio of TCH/HDL [28]. Moreover, the TCH/HDL and TAG/HDL ratio correlates with the degree of hepatic fat [29]. Among markers for insulin resistance as well as predisposition to CVD, current research has focused on the TAG/HDL ratio, being the best predictor of insulin resistance [30]. In addition to this, in our experiment, after 8 weeks of feeding, WD\({}_{\rm ch}\) rats had the highest (among all groups) serum uric acid (UA) levels. Uric acid is a weak acid (pKa = 5.75) and almost all circulates in the serum as monosodium urate [31]. [PERSON] et al. [32] suggested that uric acid may affect lipid metabolism in rats, causing abnormal lipid levels. Knowing that dyslipidemia is a crucial risk factor for atherosclerosis, hyperuricemia should, therefore, be considered as an important agent in the occurrence and development of this disease [32]. The effect of the LCHP diet enriched with 1% cholesterol (LCHP\({}_{\rm ch}\) group) on the activity of hepatic enzymes (ALT and AST) was observed in our study. Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) measurements are considered precise liver function tests. It is known that high levels of such enzymes confirm liver damage, which involves hepatocyte destruction [2,33]. In our previous article, we showed a significant increase in liver weight in rats fed the LCHP diet (as compared to control AIN-93G), whereas liver aminotransferase activities were unchanged. However, it is known that the absence of elevated liver enzymes does not exclude NAFLD diagnosis [11]. In the present study we observed increased ALT activity, without statistically significant alterations in AST level. On the other hand, [PERSON] et al. [34] shown an increase in the level of liver enzymes, with the same degree of increase in dietary protein content.