Changes in diet and lifestyle in recent years have led to unhealthy dietary patterns and inadequate physical activity, making it difficult to maintain an appropriate energy balance, which results in an increased prevalence of diet-related chronic diseases such as obesity, diabetes, cardiovascular disease, and certain types of cancer. The importance of the roles of lipids in these diseases is now recognized. Dietary fatty acids modulate inflammatory processes and contribute to the pathophysiological state of diet-related chronic diseases. Although there is insufficient evidence as to the involvement of monounsaturated fatty acids in inflammatory processes and limited evidence indicating a potential proinflammatory role of saturated and trans fatty acids, there is considerably stronger evidence suggesting that increasing the intake of n-3 polyunsaturated fatty acids brings about favorable antiinflammatory effects. Certain fatty acids may also produce therapeutic effects by modifying the activity of ghrelin, a growth hormone-releasing and appetite-stimulating peptide; such modification may yield reduction of food intake and enable clinical manipulation of energy metabolism.