Objective To estimate the daily dietary energy intake for me to maintain a constant body weight. How hard can it be? Design Very introspective study. Setting At home. In lockdown. (Except every Tuesday afternoon and Saturday morning, when I went for a run.) Participants Me. n=1. Main outcome measures My weight, measured each day. Results Sleeping, I shed about a kilogram each night (1.07 (SD 0.25) kg). Running 5 km, I shed about half a kilogram (0.57 (SD 0.15) kg). My daily equilibrium energy intake is about 10 000 kJ (10 286 (SD 201) kJ). Every kJ above (or below) 10 000 kJ adds (or subtracts) about 40 mg (35.4 (SD 3.2) mg). Conclusions Body weight data show persistent variability, even when the screws of control are tightened and tightened.