As both a cause and consequence, reactive oxygen and nitrogen species (ROS/RNS) and inflammation are essential for signalling, defence, and tissue repair, yet when chronically elevated, they drive metabolic dysfunction. These processes are closely linked through major pathways that regulate cytokine production, immunity, and cellular stress responses. Nutrition plays a central role in modulating oxidative stress and inflammation. While micronutrients such as vitamins C and E, zinc, and macronutrients like omega-3 and omega-6 fatty acids can exert antioxidant or pro-oxidant effects depending on context, protein and amino acids also significantly influence these pathways. Glutamine, the most abundant amino acid in the body, supports antioxidant defences through glutathione and GPx, enhances heat shock protein responses, and helps maintain cellular homeostasis and survival. Plasma glutamine levels fluctuate in response to metabolic stress, and low concentrations are associated with poorer clinical outcomes. Although glutamine has traditionally been administered intravenously in critical-care settings, recent studies have clarified the effects of oral supplementation by examining glutamine kinetics, dosage, and frequency. Oral doses of 15–30 g (approximately 0.1 g/kg) can increase plasma glutamine levels from a baseline of 500–800 μM, peaking within 30–60 minutes before declining over 2–4 hours, indicating that multiple doses administered over 24 hours are required for sustained availability. This helps explain why intravenous glutamine often produces stronger effects, and why chronic supplementation in animal studies yields greater improvements in cellular stress and inflammation than acute dosing. Emerging evidence also suggests a role for glutamine in pathways related to obesity-induced diabetes. Overall, oral intakes of 0.3–1.0 g/kg/day may be effective; however, the frequency of administration is likely the key determinant of benefit. Further research is needed to confirm these findings in humans and to advance personalised amino acid strategies for specific catabolic conditions.