Unintended Consequences of Obesity Pharmacotherapy: A Nutritional Approach to Ensuring Better Patient Outcomes

Background/Objectives: Obesity pharmacotherapy vastly improved the treatment of the disease of obesity. However, GLP-1 receptor agonists and GIP/GLP-1 dual agonists may lead to nutritional complications, including severe caloric restriction, micronutrient deficiencies, lean body mass loss, dehydration, and ketosis. We examine these risks and outlines dietitian-led strategies to support improved safety and effectiveness. Methods: This narrative review was conducted in three stages: literature search, screening of abstracts and full texts, and synthesis of findings. Searches were carried out in April and May 2025 across PubMed, Embase, Scopus, ScienceDirect, Web of Science, and Google Scholar using keywords related to obesity pharmacotherapy and nutrition. Results: Clinical observations and trial data suggest that some individuals may consume fewer than 800 kcal/day during the initial stages of treatment. Prolonged energy and protein deficits can increase the risk of sarcopenia, metabolic dysfunction, and reduce treatment adherence. Additional risks include inadequate micronutrient intake due to reduced dietary variety, dehydration linked to gastrointestinal symptoms and hypodipsia, and rare but serious cases of ketoacidosis. Patients at heightened risk include older adults, those with low baseline muscle mass, and individuals with restrictive eating patterns. Conclusions: Obesity medications introduce unique nutritional risks that are not yet addressed by standardised clinical protocols. Registered dietitians play a critical role in assessing intake patterns, monitoring for red flags, and delivering targeted nutritional support. Integrating structured dietary assessment tools, checklists, and risk-specific guidance into pharmacotherapy pathways can enhance safety, promote adherence, and improve long-term outcomes.