Why does my weight go up and down?
Last updated September 3, 2026.
Daily swings of 2 to 5 pounds are water and gut content, not fat: salt, carbs, hormones, workouts, alcohol, and bathroom timing all move the number within days. The mechanics: salty meals hold water for a day or two; each gram of stored carbohydrate carries about 3 grams of water, so carb-heavy or low-carb days swing the scale fast; pre-period hormones add 1 to 5 pounds that vanish with bleeding; hard workouts hold water in muscles for 24 to 72 hours. The protocol: weigh weekly, same day and conditions (morning, post-bathroom, pre-breakfast, same scale), and read the 4-week trend, not the daily number; daily weighers should average the week and compare averages. Signals that mean something: a steady 2-to-3-month upward drift (a real surplus), a 4-plus-week plateau on an honest deficit (recalibrate or rule out medical causes), or unexplained loss without trying (a doctor visit). If the daily number steers your mood, weekly weighing is the fix, not a compromise.
What to do
- Water moves the scale: salt, carbs, hormones, workouts.
- Weigh weekly, same conditions, or average the week.
- Judge the 4-week trend, never a single day.
- 2-3 month upward drift: audit intake.
- Dropping without trying: see a doctor.
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