Why does the scale move three pounds in a day?
Answer
Because most of what a daily scale reading measures is water, food in transit and glycogen, not fat.
In more detail
Day-to-day variation of a few pounds is normal in either direction and is dominated by hydration, sodium, carbohydrate intake and where you are in a menstrual cycle. Trials read weight as a trend across weeks for exactly this reason. A single reading is close to meaningless; four weeks of readings is a signal. If daily weighing is making a flat two weeks feel like a crisis, the fix is usually the reading frequency rather than the medication.
Source
Standard clinical trial weight measurement practice.
Educational use only, never medical advice. No doses.