When your weight stops moving

A review of 80 studies lasting at least a year shows a typical pattern: weight falls on average by 5 to 8.5 kg in the first 6 months and then roughly stops.^[4] A diet trial of 811 people found the same shape. On all four diets weight went down for 6 months, and from month twelve some of it came back.^[5]

A mathematical model explains why this happens even without mistakes: the body responds slowly to a lasting change. It takes about a year to get half of the way to a new weight.^[6]

As weight falls, so does expenditure. According to a review, appetite plays an even larger part, because the body works against further loss.^[1] One calculation estimates that people eat about 100 kcal more a day for each kilogram lost.^[2]

You hear this a lot, but the data are more sober. Of 33 studies with 2,528 people, most reported an adaptation, yet well-run studies found small values or none. Once weight was stable it tended to fade.^[7]

After losing about 12 kg, the resting metabolism of 171 women was 54 kcal a day below the expected value. That did not predict later regain.^[8] During a strict diet the gap can be larger: in 71 people on 1,000 kcal a day it was 92 kcal after 8 weeks.^[9]

So energy use falls mainly because a lighter body needs less. Your metabolism is not broken.

Weight changes even during a normal week.^[3] A few equal values are not yet a plateau. The mean over several weeks says more. See Why the scales go up and down.

• Look at your needs again: if you log your weight, the app uses the newest value.
• Check your entries: portions often grow unnoticed, and drinks count too.
• Keep your weight: this is also a good decision if a further deficit does not fit your life right now.

If the plateau weighs on you or you keep eating less, read When to get medical advice.

The results differ. In a small study of men, those with two-week breaks lost more, but it took them almost twice as long.^[10] In 61 trained adults, three one-week breaks gave no advantage for fat or muscle, though participants felt less hungry.^[11]

After a break week, weight rose by 0.6 kg in a sub-study without any added body fat.^[12] Don't let that fool you.

So a break is fine if you need some air. No study has shown that it ends a plateau you have already reached.

• Cutting hard: In a Swedish analysis with 3,320 people per group, a 500 kcal diet led to gallstones with a hospital stay about three times as often as a 1,200 to 1,500 kcal diet. The absolute risk was low.^[13]
• Doubting yourself: Estimating food and movement is hard. In a small study, people who did not lose weight despite eating little were well off on both, and their metabolism was normal.^[14] This is not about blame.
• Judging by speed: In 200 people, as much came back after fast loss as after slow loss.^[15] What you can keep up matters more.

What comes next is under Keeping weight off.