You step on the scale Monday: 68 kg. You step on it Friday: 71 kg. You haven't changed a single habit. What happened? Your hormones happened. And the number means almost nothing.

The Fluid Retention Reality

Estrogen and progesterone directly influence how your body retains water. In the days before your period, progesterone drops sharply, causing your body to retain sodium — and therefore water. This alone can add 1–3 kg overnight, with no change in fat mass whatsoever. This is not weight gain. This is physics.

Glycogen Storage

Each gram of glycogen is stored with approximately 3 grams of water. A higher-carb day — which your body naturally craves in the luteal phase — can show as 1–2 kg on the scale the next morning. Again: not fat gain. Glycogen and its accompanying water weight fluctuates constantly.

Inflammation & Digestion

Prostaglandins — the compounds that trigger uterine contractions — also affect your gut. Slower motility, bloating, and increased intestinal inflammation all add to scale weight without reflecting any change in actual body composition.

What Actually Matters

• How your clothes fit over time — not day to day
• Energy levels, strength, and endurance across your cycle
• Monthly trends compared at the same cycle phase
• How you feel in your body during daily activities