Why your deficit keeps shrinking as you lose weight
You were losing well, then the scale stuck. Your plan is not broken. A smaller body burns fewer calories, so your same food now makes a smaller gap.
You were losing a kilo a week. You felt great. Then the scale got stuck. You did not change your food. You did not get lazy. So what happened? Your body got smaller. A smaller body burns less fuel, even at rest. The same meal plan that once made a big gap now makes a small one. This short read shows the maths, and what to do next.
Every kilo you lose drops your burn by about 10 kcal a day
Here is the rule behind the slowdown. The most-used calorie formula is called Mifflin-St Jeor. In that formula, the number for body weight is 10. That means each kilo of your body adds about 10 kcal to your daily burn. So if you lose 10 kg, your body burns about 100 kcal less each day, just from being lighter. This is not a guess. It is built into the maths every calorie app uses. Losing weight is winning. But winning also makes the gap smaller.
One man, two weights: see the gap shrink
If my weight loss has slowed down, my metabolism must be broken.
mostly falsemostly false
Most of the slowdown is just the maths above. A lighter body burns less. Scientists have also found a small extra drop they call 'metabolic adaptation'. Your burn can fall a little more than the weight loss alone explains. But the word 'broken' is wrong. Your body is doing what bodies do when they get smaller. Re-run your numbers and nudge the gap open again. You are not broken. You are just further along.
What to do when your deficit shrinks
The bottom line
Your deficit shrank because you weigh less. That is the plan working, not failing. Every 10 kg you lose takes about 100 kcal a day off your burn. So every 5 kg or so, re-run the maths and nudge the gap open again. You did not break anything. You just moved to the next level.