Dietary lipids play an important role in human health status, especially in the modulation of lipoprotein metabolism and consequently atherosclerosis and the development of other chronic diseases. Epidemiological studies have confirmed a strong association between fat intake, especially saturated fat, mean total cholesterol levels, and cardiovascular mortality rates worldwide. The influence of dietary cholesterol intake is small compared to the effect of saturated fatty acids and varies among individuals. This article deals with the importance of dietary lipids in human nutrition according to the content of different fatty acid categories. Fatty acids are categorized into four classes: saturated, monounsaturated, polyunsaturated and trans-fatty acids. Saturated fatty acids increase LDL-cholesterol concentrations, while polyunsaturated fatty acids decrease LDL-cholesterol level, though to a lesser extent. All fatty acids increase HDL-cholesterol levels. Trans-fatty acids are unsaturated fatty acids that have one or more double bonds in the trans configuration (sources are milk products and meat from ruminant animals and/or certain processed foods). Trans-fatty acids have an adverse effect on blood lipids due to the elevation of LDL-cholesterol and decrease of HDLcholesterol. Therefore, the most favourable lipoprotein profile for the prevention of coronary heart disease and other chronic diseases can be achieved if saturated fatty acids are replaced by unsaturated ones. Preventive medicine needs to focus on changes in dietary habits with emphasis on fat modification. A diet low in total fat, primarily avoiding saturated and transfatty acids but rich in unsaturated fatty acids (mainly n-3 fatty acids in fish oils), should be recommended.