1. A method of treating dyslipidemia in a subject in need thereof, comprising peripherally administering an effective amount of a melanocortin-4 receptor agonist to treat dyslipidemia in said subject in need thereof. 2. The method according to claim 1, wherein said treatment of dyslipidemia occurs as a result of a decrease in serum cholesterol, triglycerides, low density cholesterol lipoprotein, free fatty acids, or an increase in high density cholesterol lipoprotein, or any combination thereof. The method of claim 1, wherein said subject suffers from steatosis of the liver. The method of claim 3, wherein said liver steatosis is a non-alcoholic fatty liver disease or alcoholic fatty liver disease. The method according to claim 4, wherein said non-alcoholic fatty liver disease or alcoholic fatty liver disease is accompanied by steatonephritis, steatonecrosis, inflammation of the liver, ballooning degeneration, fibrosis, cirrhosis or cancer, or any combination thereof. The method of claim 1, wherein said melanocortin receptor-4 agonist used to treat dyslipidemia is selected from the group consisting of the following compounds: Ac-Arg-c (Cys-D-Ala-His-D-Phe-Arg-Trp- Cys) -NHAc-Nle-c (Asp-His-D-Phe-Arg-Trp-Ala-Lys) -NH； Ac-Nle-c (Asp-His-D-Phe-Arg-Trp-A6c-Lys) -NH； Ac-Nle-c (Cys-His-D-Phe-Arg-Trp-Ahx-Cys) -NH； D-Phe-c (Cys-His-D-Phe-Arg-Trp-Ala-D- Cys) -Thr-NH； D-Phe-c (Cys-His-D-Phe-Arg-Trp - Ala-D-Cys) -Thr-NH； D-Phe-c (Cys-His-D-Phe -Arg-Trp-Gaba-D-Cys) -Thr-NH； Ac-Nle-c (Cys-His-D-Phe-Arg-Trp-Apn-Cys) -NH； Ac-Nle-c (Asp-His -D-Phe-Arg-Trp-Apn-Lys) -NH； Ac-A6c-c (Asp-His-D-Phe-Arg-Trp-Gaba-Lys) -NH； Ac-D-2-Nal-c (Asp-His-D-Phe-Arg-Trp-Gaba-Lys) -NH； Ac-Cha-c (Asp-His-D-Phe-Arg-Trp-Gaba-Lys) -NH； Ac-Nle-c (Asp-His-D-Phe-Arg-Trp-Gaba-Lys) -NH； Ac-Nle-c (Cys-D-Ala-His-D-Phe-Arg-Trp-Cys) -NH； Ac-Nle -c (Cys - Ala-His-D-Phe-Arg-Trp-Cys) -NH； Ac-Nle-c (Cys-Gaba-His-D-Phe-Arg-Trp-Cys) -NH ； Ac-Nle-c (Cys-Aib-His-D-Phe-Arg-Trp-Cys) -NH； Ac-Nle-c (Cys-Gly-His-D-Phe-Arg-Trp-Cy
