Core Insights - The article discusses the metabolic reprogramming that occurs during critical illness, emphasizing the role of inflammation and immune response in altering energy distribution and substrate utilization within the body [6][9][27]. Metabolic Regulation Principles - The priority of substrate utilization shifts during critical illness, with the body first consuming glucose and glycogen, followed by fats and proteins. This shift is crucial for supporting immune and inflammatory cell needs, leading to significant breakdown of muscle and fat tissues [10][13]. - The liver and kidneys enhance gluconeogenesis during critical illness, utilizing lactate, glycerol, and amino acids as substrates, which is vital for maintaining glucose levels [13]. Immune and Inflammatory Cell Metabolism - Immune cells, particularly M1 macrophages and activated T cells, primarily rely on aerobic glycolysis (Warburg effect) for rapid ATP production and biosynthetic precursors, supporting inflammatory responses despite lower energy efficiency [16][18]. - Metabolites such as succinate and itaconate can epigenetically regulate gene expression, influencing inflammation and immune responses [17]. Muscle and Fat Tissue Metabolic Remodeling - In critical illness, white adipose tissue may convert to brown adipose tissue, enhancing thermogenic capacity, while the phenomenon known as the "obesity paradox" suggests that obese individuals may have better survival rates due to greater energy reserves and anti-inflammatory factors [20][22]. - Muscle protein breakdown is significantly increased due to enhanced ubiquitin-proteasome and autophagy mechanisms, leading to muscle wasting [22][26]. Conclusion - The body undergoes metabolic reprogramming during critical illness to enhance immune defense and survival, with a focus on the roles of immune cell metabolism and the breakdown of muscle and fat tissues. Future research should explore innovative interventions targeting metabolic pathways to improve clinical outcomes for critically ill patients [27].

Core Insights - The article discusses the metabolic reprogramming that occurs during critical illness, emphasizing the role of inflammation and immune response in altering energy distribution and substrate utilization within the body [6][9][27]. Metabolic Regulation Principles - The priority of substrate utilization shifts during critical illness, with the body first consuming glucose and glycogen, followed by fats and proteins. This shift is crucial for supporting immune and inflammatory cell needs, leading to significant breakdown of muscle and fat tissues [10][13]. - The liver and kidneys enhance gluconeogenesis during critical illness, utilizing lactate, glycerol, and amino acids as substrates, which is vital for maintaining glucose levels [13]. Immune and Inflammatory Cell Metabolism - Immune cells, particularly M1 macrophages and activated T cells, primarily rely on aerobic glycolysis (Warburg effect) for rapid ATP production and biosynthetic precursors, supporting inflammatory responses despite lower energy efficiency [16][18]. - Metabolic intermediates can epigenetically regulate gene expression, influencing inflammation and immune responses [17]. Muscle and Fat Tissue Metabolic Remodeling - In critical illness, white adipose tissue may convert to brown adipose tissue, enhancing thermogenic capacity, while obesity paradox suggests that obese individuals may have better survival rates due to greater energy reserves and anti-inflammatory factors [20][22]. - Muscle protein breakdown is significantly increased due to enhanced ubiquitin-proteasome and autophagy mechanisms, leading to muscle wasting [22][26]. Conclusion - The body adapts through metabolic reprogramming during critical illness to enhance immune protection and survival, with a focus on the roles of immune cell metabolism and the breakdown of muscle and fat tissues. Future research should explore innovative interventions targeting metabolic pathways to improve clinical outcomes for critically ill patients [27].

Core Viewpoint - The article discusses the metabolic reprogramming in critically ill patients, emphasizing the importance of understanding energy flow and immune response mechanisms to improve treatment outcomes [6][9][27]. Metabolic Regulation Principles - The priority of substrate utilization in normal conditions is glucose and glycogen first, followed by fats and proteins. In critical illness, metabolism prioritizes the needs of immune and inflammatory cells, leading to significant breakdown of muscle and fat tissues to support immune cell synthesis [10][11]. - The liver and kidneys significantly enhance gluconeogenesis during critical illness, utilizing lactate, glycerol, and amino acids as substrates, with the Cori cycle playing a key role in glucose regeneration [13]. Immune and Inflammatory Cell Metabolic Reprogramming - Immune cells, such as M1 macrophages and activated T cells, primarily rely on aerobic glycolysis (Warburg effect) for rapid ATP production and biosynthetic precursors, which supports inflammatory responses but has a lower energy yield compared to mitochondrial metabolism [16][18]. - Metabolites like succinate and itaconate can regulate gene expression through epigenetic modifications, influencing inflammation and immune responses [17]. Changes in Adipose Tissue and Skeletal Muscle - In critical illness, white adipose tissue may convert to brown adipose tissue, enhancing thermogenic capacity. The "obesity paradox" suggests that obese individuals may have better survival rates in critical conditions due to greater energy reserves and anti-inflammatory factors [20]. - Muscle protein breakdown is significantly increased due to enhanced ubiquitin-proteasome and autophagy mechanisms, leading to muscle wasting and potential long-term functional impairments post-recovery [22][26]. Conclusion - The body adapts through metabolic reprogramming during critical illness to enhance immune defense and survival, with a focus on the roles of immune cell metabolism and the breakdown of skeletal muscle and adipose tissue. Future research should explore innovative interventions targeting metabolic pathways to improve clinical outcomes for critically ill patients [27].