Extremely restrictive diets among young adults—often influenced by social media—can cause acute metabolic instability. Symptoms may appear nonspecific, and individuals may attend routine visits rather than present with clear complaints. In primary care, detailed nutritional history is essential to identify high-risk dietary patterns and prevent serious outcomes. Lifestyle-focused assessment helps contextualize subtle presentations and supports early intervention.A 23-year-old woman visited a family health center for routine weight monitoring and laboratory evaluation. She reported following a “water diet” for one month, consuming 1–1.5 liters of water and occasional low-calorie liquids, with nearly no solid food. She experienced rapid weight loss (7–9 kg/month), palpitations, fatigue, cold extremities, and menstrual delay. Shortly after leaving the examination room, she developed sudden dizziness and brief loss of consciousness. Reassessment showed hypotension (85/55 mmHg), tachycardia (112 bpm), reduced skin turgor, and capillary glucose of 59 mg/dL. She improved quickly with positioning and oral glucose. Suspecting metabolic disturbance, she was urgently referred for testing. Laboratory results revealed mild hypoglycemia, electrolyte imbalance, ketonuria consistent with starvation ketosis, mild metabolic acidosis, and low ferritin with mild anemia. At follow-up, the metabolic consequences of extreme caloric restriction were explained. Motivational interviewing addressed her weight-loss motives and psychosocial influences. A gradual caloric restoration plan, hydration guidance, healthy plate education, and counseling on safe weight management were provided.Although restrictive dieting is common, this case demonstrates syncope directly linked to a social-media-driven diet trend, emphasizing the ability of primary care to identify metabolic crises through lifestyle-focused assessment.Young adults may adopt extreme diets without recognizing risks. Early lifestyle-oriented questioning can prevent severe metabolic consequences and reduce emergency visits. Structured nutrition screening in routine assessments may help counter unsafe diet trends.The patient’s syncope was explained by caloric deprivation, ketosis, and hypoglycemia. Evidence supports motivational interviewing and gradual caloric reintroduction as effective first-line strategies.Extreme dieting can cause acute metabolic instability and syncope. Comprehensive nutritional assessment and patient-centered counseling in primary care enable timely recognition and safer recovery. MeSH:Syncope, Starvation, Metabolic Disorders, Nutrition Assessments