Energy metabolism at whole-body, cellular, and even organelle, i.e., mitochondrial, levels requires adequate regulation in order to maintain or improve (metabolic) health. In eukaryotic cells, mitochondria are key players in energy (ATP) production via oxidative phosphorylation. Both macro- and micronutrients potentially influence energy metabolism and mitochondrial functioning, either as substrates for (oxidative) catabolism or as essential constituents of enzymes or protein complexes involved in (mitochondrial) energy metabolism. This book contains a valuable collection of empirical preclinical and human studies to assist in the development of understanding and progress this area of research on improving health and, more specifically, metabolic health.