The chapter discusses the role of mitochondrial dynamics in regulating nutrient utilization and energy expenditure. Mitochondrial fusion, fission, and mitophagy are essential for quality control, but recent studies suggest that these processes also play a role in adapting to metabolic demands. Changes in mitochondrial architecture can influence bioenergetic efficiency and energy expenditure, with connected or fragmented structures favoring different outcomes. The authors propose that the conflict between bioenergetic adaptation and quality control may contribute to mitochondrial dysfunction in age-related diseases. They highlight the importance of understanding how nutrients and metabolic states regulate mitochondrial dynamics in different tissues, such as brown adipose tissue, muscle, and beta-cells, to grasp the mechanisms underlying metabolic and aging conditions. The chapter also explores the relationship between mitochondrial dynamics and bioenergetic efficiency, noting that changes in dynamics can modulate bioenergetic efficiency and vice versa. It discusses the effects of nutrient excess on mitochondrial bioenergetics in various tissues and the specific mechanisms involved in beta-cell adaptation to nutrient availability. Overall, the chapter emphasizes the dynamic nature of mitochondrial architecture and its critical role in maintaining cellular function under different physiological and pathological conditions.The chapter discusses the role of mitochondrial dynamics in regulating nutrient utilization and energy expenditure. Mitochondrial fusion, fission, and mitophagy are essential for quality control, but recent studies suggest that these processes also play a role in adapting to metabolic demands. Changes in mitochondrial architecture can influence bioenergetic efficiency and energy expenditure, with connected or fragmented structures favoring different outcomes. The authors propose that the conflict between bioenergetic adaptation and quality control may contribute to mitochondrial dysfunction in age-related diseases. They highlight the importance of understanding how nutrients and metabolic states regulate mitochondrial dynamics in different tissues, such as brown adipose tissue, muscle, and beta-cells, to grasp the mechanisms underlying metabolic and aging conditions. The chapter also explores the relationship between mitochondrial dynamics and bioenergetic efficiency, noting that changes in dynamics can modulate bioenergetic efficiency and vice versa. It discusses the effects of nutrient excess on mitochondrial bioenergetics in various tissues and the specific mechanisms involved in beta-cell adaptation to nutrient availability. Overall, the chapter emphasizes the dynamic nature of mitochondrial architecture and its critical role in maintaining cellular function under different physiological and pathological conditions.