Weight loss
Why You Lose Weight So Fast in the First Week of a Diet
Week one: minus 2.8 kg, pure euphoria. Week two: minus 0.4 kg, pure confusion. Nothing went wrong. Here is what those two numbers actually mean.
Quick answer
First-week losses of 1 to 3 kg are mostly water: cutting calories (especially carbs) empties glycogen stores, and each gram of glycogen holds about 3 grams of water. Real fat loss settles in at roughly 0.5 to 1 kg per week from week two onward.
Where the first kilos come from
Eating less empties your glycogen stores, the carbohydrate fuel in your muscles and liver, and every gram of glycogen binds about 3 grams of water. Add a lighter gut content from smaller meals, and 1 to 3 kg vanishes before any meaningful fat is gone.
Why week two feels like a wall
Once the water is out, the scale shows plain fat loss, and fat leaves slowly: a 500 kcal daily deficit is about half a kilo per week. That is not a plateau, it is the diet working at its real speed.
The trap: chasing week one forever
People cut harder to recreate the week-one drop, burn out, and quit. Judge your diet by the monthly rate from week two onward, not by the opening sprint.
What to do with this
Enjoy the early drop, then switch your expectations: 0.5 to 1 kg per week is winning. Weigh daily, read the trend, and remember the water comes back instantly when you refeed, which is just as meaningless in reverse.
Common questions
How much weight do you lose in the first week of a diet?
Commonly 1 to 3 kg, of which the majority is water from emptied glycogen stores and lighter gut content. Fat loss in week one is usually 0.3 to 0.7 kg.
Why did my weight loss slow down after the first week?
The water portion is gone and the scale now shows pure fat loss, which runs at roughly 0.5 to 1 kg per week on a sensible deficit. Slower after week one is normal, not failure.
Will the water weight come back after the diet?
Yes, refilling glycogen stores brings 1 to 2 kg of water back within days of eating normally. It is refilling, not fat regain; judge maintenance from your new baseline.
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