The most likely explanation: your first-month result included several kilos of water weight and glycogen loss, which made the scale drop faster than sustainable fat loss alone. When the body stabilises, small fluctuations — including a temporary 1–2kg increase — are completely normal. A 2kg gain while maintaining the same routine is rarely genuine fat regain. It is almost always water, glycogen, hormonal changes, or a small drift in habits that is difficult to notice from the inside.
When you start intermittent fasting — particularly if you also reduced carbohydrates or processed foods — the first kilos you lose are a combination of:
Glycogen and water: Your liver and muscles store roughly 400–500g of glycogen. Each gram of glycogen holds approximately three grams of water. When glycogen depletes in the first week or two, you can drop 1–3kg of water weight almost overnight. This is real weight loss — but it's not fat loss. It's stored energy and the water bound to it.
Reduced inflammation: Cutting out sugar and processed food reduces systemic inflammation quickly, and with it some fluid retention. This can show up as rapid early weight loss that the body later adjusts.
Early fat burning: Real fat loss does happen in the first month — but at a slower rate than the scale initially suggests. A realistic rate of fat loss is 0.5–1kg per week under consistent fasting conditions with good food quality.
This creates a misleading early picture. The scale drops fast in week one or two, motivation rises — and then the rate slows and stabilises, because the glycogen event was a one-time occurrence.
Two kilograms of genuine fat requires approximately 14,000 calories above your maintenance needs. Unless there was a significant change in eating — a holiday, a sustained period of stress eating, several social meals — 2kg of true fat gain in a single month while continuing to fast is essentially impossible.
More likely causes of a 2kg increase:
Glycogen refilling: Any increase in carbohydrate intake — even from foods that seem healthy, like fruit or root vegetables — refills glycogen stores and brings water back with it. A single higher-carbohydrate day can add 1–2kg on the scale by the following morning.
Hormonal fluctuation: In women, the luteal phase (the week before a period) causes natural water retention of 1–3kg driven by progesterone. This is not fat, it is temporary, and it reverses after menstruation begins.
Eating window drift: It's easy for the eating window to shift 30–45 minutes over time without noticing. What began as a strict 16-hour fast can gradually become closer to 14 hours. Small drifts compound over weeks.
Food quality changes: A few extra meals with more carbohydrates, sauces with hidden sugars, or slightly larger portions can refill glycogen without feeling like a significant change.
Higher sodium intake: Eating saltier food than usual leads to water retention within 24–48 hours, which shows on the scale without any change in body fat.
This is worth examining honestly. Habits drift. In the first month, everything is new and attention is high. By month two, it becomes easier to:
None of these are failures — they're entirely normal human behaviour. But they can explain a 2kg difference without feeling like anything changed.
Two kilograms is within the range of normal daily fluctuation for most adults. The scale measures everything in the body: water, food mass, waste, glycogen, and fat. It is not a precise measure of fat loss, and a single reading does not tell you which of these has changed.
Better progress markers than the scale:
A 2kg scale fluctuation with stable waist measurement is almost certainly water — not fat regain.
Don't over-correct. A dramatic restriction in response to a small fluctuation often backfires, triggering hunger, cortisol elevation, and paradoxical weight gain.
Review your eating window honestly. What time does it actually open and close on most days? Track for three days and compare to month one.
Check food quality. Has anything changed — a sauce, a drink, a snack that wasn't there before? Even small additions can shift the balance.
Stay consistent for another 2–3 weeks before drawing conclusions. A single weigh-in showing 2kg higher does not mean the trend has reversed. Weekly averages are far more informative than daily readings.
Want to learn more? Read our full article: Why did I stop losing weight on intermittent fasting?
Track every fast automatically — get FastSyncer on the App Store — your first week is free.
This is for informational purposes only and is not medical advice.