Plateaus, regain and keeping weight off

Every fast weight loss slows down, and most of it comes back unless something is holding it off. That is not a personal failing. It is how a body that has lost a lot of weight behaves. Knowing that in advance is the difference between a plateau you plan for and one that ends the whole thing.

Why plateaus happen

Two things slow weight loss down, and neither is a sign you are doing it wrong.

A smaller body needs less. Every kilogram you carry costs energy to keep alive and to move around. Lose 20 kg (3 st 2 lb) and the number of calories that used to make you lose weight becomes the number that keeps you stable. The deficit shrinks as you do.

The body fights back. On top of that, after big weight loss the body burns fewer calories than its new size would predict. The best-known measurement comes from 14 contestants in the American television show The Biggest Loser. They lost an average of 58 kg in 30 weeks. Six years later they had regained about 41 kg on average, and their resting metabolic rate was still around 700 kcal a day below where it started, roughly 500 kcal a day lower than expected for their body size. The researchers called this metabolic adaptation; it is also known as adaptive thermogenesis, and it seems to be proportional to how hard the body is being pushed to lose.^[1]

That is an extreme example, from extreme weight loss with extreme exercise. But the direction is the same for everyone: as weight falls, the body turns down the thermostat and turns up the hunger. It does this whether the loss came from diet, surgery or a medicine. Keeping muscle helps, because muscle burns more at rest than fat, which is one reason preserving muscle matters so much.

Set points and why regain is physiology, not failure

The idea of a "set point" is that the body defends the weight it is used to: when you drop below it, hunger rises and energy use falls until you drift back. The details are still argued over, but the pattern in the data is not: after weight loss, the body behaves as if it wants the weight back, and the effort needed to keep it off does not go away.^[1] Medicines in the GLP-1 class work partly by quieting those signals. Take the medicine away and the signals return.

That reframing matters. People who regain weight after stopping a medicine, a programme or a diet tend to blame themselves. The trial evidence says the regain is what the body does, and that a treatment that stops is a treatment that stops working.

What regain after stopping looks like in the trials

STEP 1 extension (semaglutide). In the main trial, participants lost an average of 17.3% of their body weight over 68 weeks. After the drug and the lifestyle support were withdrawn, they regained 11.6 percentage points by week 120, a year later: about two-thirds of what they had lost. Improvements in blood pressure, blood fats and blood sugar largely reverted towards where they started.^[2]

SURMOUNT-4 post hoc analysis (tirzepatide). People who had lost weight on tirzepatide were switched to placebo. Within a year, most had regained at least 25% of the weight they had lost, and those who regained more saw their cardiometabolic gains reverse in proportion.^[3]

TRIUMPH-6 (retatrutide). Lilly is running a dedicated weight-maintenance trial of retatrutide in 643 people, registered as NCT06859268, with completion expected around April 2028.^[4] Until it reports, there is no evidence on what happens to weight after stopping retatrutide. Given the two trials above, the sensible assumption is that it is not different in kind. Nothing on this site about retatrutide's trial results applies to anything sold online as retatrutide; see TRIUMPH-1 for the results themselves and the safety section for why the products are different.

Habits that survive without a drug

The 2025 nutrition advisory summarises what people who keep weight off long-term tend to have in common, drawing on the US National Weight Control Registry: eating at regular times, eating breakfast, choosing minimally processed foods higher in protein and fibre, avoiding sugary drinks and snack foods, allowing occasional planned treats rather than severe restriction, and regular physical activity.^[5] In practice:

1. Protein at every meal, for life, not just during the loss. It keeps you fuller and keeps your muscle. See the protein page.
2. Two strength sessions a week, permanently. Muscle is your metabolic insurance, and the NHS recommends it for every adult anyway.^[6] See resistance training.
3. Daily walking. The cheapest, most sustainable calorie burn there is, and the activity most consistently linked with keeping weight off.
4. Sleep. Short sleep raises hunger and shifts loss towards muscle. See sleep and recovery.
5. A weighing routine. Once a week, same day, same time, written down. Not to obsess, but so that a 2 kg drift is caught at 2 kg, not 10.
6. An environment you control. What is in the house gets eaten. Decide at the supermarket, not at 10 pm.
7. A plan for lapses. Holidays, Christmas and bad weeks happen. Decide in advance what "back on track" looks like on the Monday after.

What maintenance realistically means

Maintenance is not a fixed number. Weight fluctuates by a kilogram or two with water, salt, hormones and the time of day. A realistic aim is a range, say 3 kg wide, and a rule for what you do when you reach the top of it.

Some regain after any large weight loss is normal and does not undo the benefit. Trials consistently show that people who keep off even half of what they lost stay healthier than where they started. If you have lost 25 kg (3 st 13 lb) and are holding at 15 kg down a year later, that is success by any clinical measure, and the same is true of a smaller loss kept off for longer.

If you are regaining steadily despite the habits above, that is a reason to talk to a GP rather than to try harder alone. NHS weight-management services exist for exactly this, and the licensed medicines are prescribed for long-term use for the same reason. The NHS and licensed options page explains how to get assessed.