The maths of a plateau — energy balance always wins eventually
Your scale was dropping, then it froze at the same weight for weeks. The maths explains why: a lighter body burns fewer calories, so your same food plan stops making a deficit. Here is how to read your own numbers and re-create the gap.
You were losing weight nicely. You logged every meal in Burnie. You walked each morning. The scale moved down week after week. Then it froze. Same food, same walk, same effort. The number just sits there. Three weeks, nothing. You want to scream. Before you blame yourself, look at the maths. A plateau is not your fault failing. It is your body's maths catching up. Energy balance always wins eventually. Here is how to read your own numbers and see it clearly.
Why a lighter body burns less (the maths)
Your basal metabolic rate (BMR) is the calories your body burns just to stay alive. Scientists have a formula for it called Mifflin-St Jeor. For a woman, it is: 10 times your weight in kg, plus 6.25 times your height in cm, minus 5 times your age, minus 161. See the first number? It is tied to your weight. So when your weight drops, your BMR drops too. Think of a 40-year-old woman who is 160 cm tall. At 85 kg, her BMR is about 1489 calories a day. At 75 kg, it is about 1389. That is 100 fewer calories burned each day, just from losing 10 kg. The same maths that rewarded you at the start now works against you. Burnie shows you this BMR number from the same formula, so you can watch it change as your weight changes.
Your numbers at 85 kg versus 75 kg
Let us put real numbers in. Say you are that 40-year-old woman, 160 cm tall. You walk daily and Burnie reads about 300 active calories from your phone. You eat 1500 calories a day. Burnie works out your deficit as food calories minus (BMR plus active calories). Watch what happens when only your weight changes.
A plateau means my diet stopped working and I am doing something wrong.
mostly falsemostly false — the maths re-balanced, the deficit shrank, and your body adapted. Your plan did not break; the number that made the deficit got smaller.
Your diet did not stop working. Your body re-ran the maths without telling you. Two things happened. First, your lighter body burns fewer calories, so the gap between what you eat and what you burn got narrower. Second, your body quietly slows down a little more than the weight maths alone predicts. Scientists call this adaptive thermogenesis. It takes more than two weeks to show up, and it adds about 120 calories a day to the slowdown. So the same food that made a 289-calorie deficit now makes only about 69. That is not failure. That is arithmetic. Energy balance always finds a new equilibrium. In one big study of people who lost a lot of weight very fast, this metabolic slowdown was still there six years later. Your plateau is the maths, not a personal flaw.
A 500-calorie deficit will keep taking off one pound a week forever.
mostly falsemostly false — that old rule ignores how your body changes as you lose weight. Weight loss curves and flattens, it does not go in a straight line.
This is the famous 3500-calorie rule. It says cut 500 calories a day and you lose one pound (about 0.45 kg) every week, forever. It sounds clean. It is wrong. Scientists tested it across seven real weight-loss studies. People lost about 20 pounds, but the old rule predicted about 28. The rule overestimates loss because it pretends your body never adapts. Real weight loss bends. It drops fast at first, then curves, then flattens. A validated maths model predicts the plateau lands at energy equilibrium, often within about a year or two. The old straight-line rule simply cannot see the curve. So when your loss slows, the maths expected it all along.
How to re-create the deficit (the maths fix)
A plateau is the maths asking you to update the inputs. Here is how to answer it. Burnie is free, so use the numbers without worry.
The bottom line
A plateau is not your willpower failing. It is the maths catching up. A lighter body burns less, and your body slows a bit more on top of that. The deficit that worked at 85 kg quietly shrinks at 75 kg. Energy balance always finds its new level. So when the scale sticks, do not panic and do not quit. Recompute your numbers, move a little more, log honestly, and re-open the gap. The maths that slowed you down is the same maths that will move you again.