Refeeding Syndrome Risk: How Cautiously to Advance Calories, and How Fast to Load Thiamine

S.V., a 16-year-old girl, has run competitive distance for her high school team since seventh grade and made varsity as a freshman, a trajectory her coaches describe as remarkable and her mother now describes, in hindsight, as the beginning of something none of them named early enough. Training mileage crept up gradually over the past year alongside a parallel, quieter restriction in what she allowed herself to eat — the two reinforcing each other in a way that read, for months, as dedication rather than illness, until she collapsed at practice ten days ago and was found, at the emergency department that day, to weigh substantially less than her team physical had recorded just three months earlier.

She is being admitted today specifically for medical stabilization and refeeding, and her intake over the past ten days — by her own accounting and her mother's independent estimate, which broadly agree — has been under 500 kilocalories most days, sometimes closer to 200. That combination of profound recent intake restriction, rapid weight loss, and a starting weight well below expected for her age and height places her squarely in the high-risk category for refeeding syndrome by every standard clinical criterion the team uses. The physiology is well characterized: prolonged starvation depletes total-body phosphate even while serum phosphate still reads normal; the moment real caloric intake resumes, an insulin surge drives glucose, phosphate, potassium, and magnesium sharply into cells, and thiamine — a cofactor multiple carbohydrate-metabolism enzymes depend on directly — gets consumed by that same sudden metabolic demand, precipitating deficiency if it isn't already replete. Everyone on the team agrees thiamine goes in before or with the very first calorie, without exception. What they don't agree on is the caloric ramp itself. The traditional, still widely taught approach starts conservatively low, historically around 5-10 kilocalories per kilogram per day, out of concern that faster refeeding directly causes the syndrome it's named for. A newer body of evidence — a multi-site randomized trial led by Garber and colleagues, comparing higher- and lower-calorie inpatient refeeding protocols in hospitalized adolescents with anorexia nervosa — found that higher-calorie refeeding, done under the same close phosphate and electrolyte monitoring either approach requires, restored weight faster and shortened hospital stay without an increase in refeeding syndrome. Her phosphate is 3.8 and her potassium 3.9 — both unremarkable on paper, and both measured before any calories have been given, which is exactly when starvation physiology hides depletion behind a normal serum value. The trial's reassurance was earned under monitoring, not instead of it, and S.V.'s heart rate of 38 sits at the edge of the population that reassurance was drawn from.