How fast should you lose weight? The honest range

Rate recommendations given in kilograms are misleading, because the same absolute loss means very different things at different body sizes. Expressing it as a percentage fixes that.

The range

0.5 to 1 per cent of bodyweight per week covers most people most of the time.

• 100 kg: 0.5 to 1.0 kg a week
• 80 kg: 0.4 to 0.8 kg
• 65 kg: 0.33 to 0.65 kg
• 55 kg: 0.28 to 0.55 kg

At the lower end you keep more muscle and find the diet easier. At the upper end you get there faster and pay for it in both.

How leanness changes the answer

This is the part usually left out.

Higher body fat. More stored energy available, so a larger deficit is better tolerated and less of the loss comes from muscle. The upper end of the range, or occasionally above it under supervision, is reasonable.

Moderate body fat. The standard range.

Already lean. The body defends remaining tissue more aggressively, and a large deficit draws more heavily on muscle. The lower end, or below it.

A useful way to think about it: the leaner you are, the more slowly you should go, and the more the last few kilograms cost.

Why faster is worse

More muscle lost. Large deficits increase the proportion of weight that comes from lean tissue, which is the thing you were trying to keep — losing fat while keeping the muscle you built.

Worse training. Performance falls, which reduces the stimulus that was protecting the muscle. A compounding problem.

More hunger. Obviously, and it is the mechanism behind most abandoned diets.

Worse adherence. The most important one. A rate you can hold for four months beats a faster one abandoned in five weeks.

Why slower is not always better

The argument for the upper end of the range is psychological and it is real. Visible results early sustain motivation, and a rate so slow that nothing changes for six weeks is its own kind of failure.

There is also the matter of time spent dieting. Very long diets accumulate fatigue, falling performance and declining adherence, so a moderate rate over three months often beats a very slow one over nine.

Reading the rate correctly

Use a seven-day weight average, compared across three weeks. Never judge from a single week.

Body water moves by a kilogram or more on sodium, carbohydrate, training and the menstrual cycle, which is more than a week's genuine loss. A week that shows zero change inside a three-week downward trend is noise — the mechanisms are in water weight: how much it hides and for how long and the method in daily weight lies, the trend does not.

Why the rate slows over time

Two causes, both normal.

A lighter body costs less to maintain and to move, so the same intake is a smaller deficit than it was.

And people unconsciously move less when eating less — fewer steps, fewer stairs, less fidgeting — which shrinks expenditure further. See steps, NEAT, and the calories you burn standing up.

The response is to recalculate the target every four to six weeks rather than to conclude that metabolism has broken, which is the diagnosis in what a weight loss plateau usually turns out to be.

The first two weeks lie

Almost everyone loses faster in the first fortnight than the deficit predicts, because lowering carbohydrate intake depletes glycogen and the water stored with it.

Two to three kilograms in two weeks is common and mostly water. It returns the moment carbohydrate does, which is why people who start with a dramatic result and then see it stall conclude the diet stopped working when it never started measuring fat.

Judge from week three onwards.

The upper limit for anyone

Losses consistently above about 1.5 per cent of bodyweight per week, outside the first fortnight, mean one of three things: a very large deficit with a correspondingly large muscle cost, substantial water loss rather than fat, or a medical issue worth investigating.

Very low calorie diets have a legitimate clinical use under supervision. They are not a self-directed strategy, and nothing here is medical advice.