Book excerpt: History has repeatedly taught us that diet-dependent nutrient deficiencies can cause a constellation of adverse symptoms (a syndrome) that are treatable and preventable by replacing the nutrient in the diet. Mammals are completely dependent on their diet to maintain optimal levels of long-chain omega-3 (LCn-3) fatty acids in cellular membranes throughout the body. It has been estimated that LCn-3 fatty acids in typical western diets have declined over the last century, largely being replaced by omega-6 fatty acids. Individuals residing in western countries commonly exhibit tissue and breast milk LCn-3 fatty acid levels that are substantially lower than those observed in individuals residing in countries that regularly consume LCn-3 fatty acids. This book, written by experts from around the world, describes what is currently known about the relationship between LCn-3 fatty acid status and resilience to different diseases. The goal of this book is to raise awareness of the importance of LCn-3 fatty acids in human health and their potential to increase resilience to several common diseases.