Reading a weight trend honestly

Most people quit a diet during a fortnight when it was working. The scale swings by more than a week of fat loss, so a real change is invisible underneath it. Here is how to see through that, and how to get a calorie number that is about you rather than about a population.

The scale is not measuring what you think

Bodyweight moves one to two kilos across a day and a week from water, sodium, glycogen and gut contents. A kilo of fat lost over a week is around 7,700 kcal of deficit — real work — and it is completely hidden by a salty dinner the night before. This is why weighing daily and reading each number is worse than useless: it gives you a signal that is mostly noise, and it punishes you at random.

Weigh often, read the average

The fix is counter-intuitive: weigh more often, not less, and never look at a single reading. A ten-day exponentially weighted average keeps what persists and drops what does not. Weigh at the same time each morning, after the toilet, before food. Missing a day is fine — the maths accounts for the gap.

Telling a plateau from an absence of information

Three weeks of a flat trend has two completely different explanations. If your weigh-ins scatter tightly around the trend, the trend is flat and that is a real plateau: something has changed, usually intake creeping up or activity drifting down. If they scatter by a kilo either side, the honest answer is that there is not yet enough information — a real half-kilo-a-week loss is smaller than your noise, and you need another fortnight rather than another change. Any tool that does not distinguish these two is guessing.

Getting a calorie number that is about you

Every app starts from Mifflin–St Jeor times an activity multiplier. The formula has a standard deviation around ±15% for an individual, and the multiplier is a shrug — so the target you are handed can be five hundred calories out before you start. If you have logged intake and weight for a fortnight you do not need it: energy in, minus energy stored, is energy out. Logging 2,000 a day while the trend falls half a kilo a week means you burned about 2,550.

The catch, stated plainly

That calculation inherits your food logging, and under-recording is the norm — commonly 10–20%, and larger for restaurant food and cooking oil. The arithmetic cannot tell the difference between burning less and writing down less, so it reads low by whatever you leave out. What it is still excellent at is change: if your habits stay the same and the figure drifts down over months, that drift is real, and it is the adaptation that makes long diets stall.

Frequently asked questions

How fast should I lose weight?

Around 0.5–1% of bodyweight a week is the usual guidance for keeping lean mass. Faster is possible and is increasingly muscle rather than fat, and it is much harder to sustain. Slower is perfectly fine and is often more durable.

Should I weigh myself every day?

For most people daily weighing plus a trend line is the most useful approach, because it gives the average something to work with. But if the number affects your mood or your eating, weigh weekly or not at all — the trend is a tool, not an obligation, and for some people it does more harm than good.

Why does my weight jump after a hard workout?

Muscle damage draws water into the tissue, and glycogen holds roughly three grams of water per gram stored. A hard session or a big carbohydrate meal can put a kilo on the scale overnight with nothing to do with fat. It comes off again; the trend never notices.