Complex lipids and their fatty acid constituents are found in every cell of the body and in many body fluids and secretions. They play structural, functional and metabolic roles that contribute to physiological homeostasis and to resilience in response to challenges, impacting cell, tissue and whole-body function and fitness, health and wellbeing, and ultimately disease risk. The number of possible lipid structures in any compartment or pool within the body is immense. For example, Quehenberger and Dennis [1] described an almost inconceivable complexity and diversity of ‘‘the human plasma lipidome’’. In this compartment alone, the diversity of lipid species out numbers the combined count of amino acid, carbohydrate and nucleic acid species 3 to 1, and this is just the plasma, never mind tissue lipid species that do not circulate. Such complexity and diversity within any body compartment and of the possible relations in lipid species across body compartments clearly poses challenges to analysis, to better understanding of function and physiology, and to gaining insight into how differences and perturbations in lipid species relate to health and disease. Thankfully, advances in analytical capabilities and in molecular and cell biology are enabling new discoveries in the lipid field that aid our understanding of the important roles of complex lipids, fatty acids and fatty acid derivatives in physiology and ‘‘normal’’function and in health and disease. Intriguingly (and unlike many other structural, functional and metabolic components of the body), blood, cell and tissue lipids are strongly influenced by the dietary intake of their precursors. This links dietary supply directly with the ‘‘lipidome’’and provides a window of opportunity for preventive and therapeutic interventions through an altered diet, and through oral supplements and enteral and parenteral administration of components deemed to be helpful in particular population or patient groups. Hence, research in lipid metabolism and therapy is flourishing and playing an increasingly important role in identifying strategies for both preventing and treating human diseases. For the first time, papers in the ‘‘Lipid metabolism and therapy’’section of the journal have been spread across two issues and these papers represent the breadth of research in the field, including research relevant to the heart, liver, adipose tissue, skin and gut and involving diet, oral supplements and parenteral nutrition.

Despite decades of research, much remains to be learned about fatty acid and complex lipid metabolism in humans and its regulation. Cross et al.[2] provide an update on regulation of de novo lipogenesis (DNL; synthesis of fatty acids and their accumulation into triglycerides) which mainly occurs in the liver. They also review the experimental techniques that can be used to assess DNL in humans. DNL is promoted by insulin and so is regulated by nutritional state; DNL is increased postprandially. Increasing carbohydrate intake increases DNL and it is now clear that fructose has a greater effect than glucose [3]; conversely restricting intake of free sugars decreases DNL [4]. The direct provision of fatty acids in the diet clearly provides substrate for triglyceride synthesis, although the impact of dietary fatty acids on DNL is modest compared with the contribution of carbohydrate. Nevertheless, some fatty acids play an important role in regulating DNL. This is most obvious for the long chain n-3 polyunsaturated fatty acids (PUFAs) which decrease the rate of DNL, mainly through actions on hepatic gene and protein expression, as also reviewed elsewhere [5]. n-6 PUFAs may also have this effect [6]. Recent research has reported that a high protein …