Why does the weight pile back on when people come off weight-loss jabs?
As a major BMJ study reported recently, they regain weight up to four times faster than those who stop conventional dieting and exercising – regaining two-thirds of the weight they had lost within a year.
The reason? It’s down to a weight ‘set point’, an internal thermostat that decides how much fat your body wants to carry.
When you’re on the jabs, they trick this internal thermostat. They reduce hunger and food noise by mimicking GLP-1, a hormone that makes the brain think it’s not hungry, and so people consume far fewer calories.
But crucially, the set point itself does not change with the jabs.
So, when the drug is stopped, the old hunger signals roar back – and the body, still convinced its ideal weight is higher, drives you to eat until you are back there.
That’s because when your weight drops below what your brain believes is safe, it reacts as though you are starving. Your metabolism slows down, hunger hormones rise and every signal in your body pushes you to eat more until you are back at what it thinks is normal.
This is not about lack of willpower, it’s about biology.
A major study reported that patients who come off fat jabs regain weight up to four times faster than those who stop conventional dieting and exercising
The set-point theory was first demonstrated in 2014. Experiments on mice that were starved until they lost half their body weight showed they always regained it once food returned – every single time, no matter how often scientists repeated the process. Their bodies simply would not allow them to stay thin. Humans are the same.
The same pattern appears in those who diet repeatedly. If you go on a low-calorie diet you may be able to lose weight short term – until the body reacts to the weight loss, and your metabolism plummets, so you burn fewer calories while hunger increases.
You may be only taking in 1,200 calories per day, but your body has gone into energy-saving mode. As well as no longer losing weight, you might feel lethargic and become starving hungry.
These symptoms aren’t psychological, they are entirely biological: it is the body trying to protect you from what it thinks is famine. Willpower may carry you through initially, but very few people can continue to be tired, irritable and extremely hungry in the long term.
That is why 90 per cent of dieters regain the weight within two years. The body is simply trying to get back to its set point.
Your weight set point is shaped by several factors, including diet, sleep and stress.
Once it is raised, your body will fight to stay there: you can open all the windows and try to cool the room down (i.e., restricting calories, going to the gym) but if the thermostat is set too high then the heating system will keep switching on to bring it up again.
The main culprit behind set points rising in the first place is ultra-processed food.
Despite the problems, Dr Andrew Jenkinson believes weight-loss drugs can be helpful and often prescribes them to patients
Modern diets packed with refined carbohydrates, sugar and industrial oils interfere with the hormone leptin, which normally tells the brain how much fat we have stored. With ultra-processed foods, the messages are blocked because they stimulate high insulin levels which dilutes the leptin signal and confuses the brain.
When this happens, the brain thinks we are starving (when, in fact, we have abundant fat) so it causes us to overeat. This raises our weight set point, in effect deciding we need to be fatter to survive.
Add in chronic stress, poor sleep and constant snacking and the problem deepens. Each of those things tells your brain you are not safe. And the body’s response to feeling unsafe is to hold on to fat.
What makes matters worse is that rapid weight loss strips muscle as well as fat. If you lose 20kg (44lb) quickly, about a third of that will be muscle.
When you put the weight back on, it all comes back as fat. So you end up with less muscle and more central abdominal fat around the organs (also known as visceral fat), which is a consequence of rapid weight regain. Visceral fat is dangerous metabolically because this type of fat releases inflammatory molecules directly into the bloodstream, contributing to serious health problems such as heart disease, type 2 diabetes, stroke and high blood pressure.
Despite these problems, I believe weight-loss drugs can be helpful – and I often prescribe them to patients.
If used carefully, they can be a bridge to a healthier lifestyle, but only if patients use the time they are on them to retrain their body. The good news is that you can lower your set point. But this takes time, over many months or even years.
This involves eating real, unprocessed food; cooking from scratch; going back to old-fashioned two or three proper meals per day – and not snacking. The reason this is important is because it keeps your blood sugar steady.
Your body gets used to a clear pattern: eat, use the energy, then rest between meals.
Snacking all the time keeps a hormone called insulin switching on and off. Insulin’s job is to move sugar from your blood into your cells so you can use it for energy. When you snack repeatedly, insulin spikes again and again.
Big spikes make your body store sugar as fat and then your blood sugar drops quickly, which can leave you tired, hungry and craving more food.
Two or three balanced meals give your body enough fuel at the right times, reduce cravings and help insulin stay level so you have steadier energy throughout the day.
Exercise also helps because it improves your cells’ response to insulin, so your body doesn’t need to produce as much of it.
When insulin levels are lower and more stable, your body is less likely to store fat and more able to burn it.
And stress management is crucial: high levels of the stress hormone cortisol tell your body to store fat.
I tell my patients to think of the process of resetting their set point as re-establishing trust.
If your body has been through years of famine signals from crash diets or erratic eating of ultra-processed foods that confuse your metabolism, then you have to convince it that it’s safe. You have to show it that the famine is over and that it can rely on real foods.
When your body feels safe, the set point naturally comes down and you will lose weight. The challenge is not to fight our biology, but to work with it. The only way of losing weight in the long term is to reduce insulin, to make the leptin signal work, so that the body then understands that you’ve got too much weight on board.
It will automatically, via its own processes, reduce your appetite, increase your metabolism – and then, without any effort, dieting or unpleasantness, you’ll reset your weight set point.
- Andrew Jenkinson is a consultant bariatric and gastrointestinal surgeon at University College London. His book, Why We Eat Too Much, is published by Penguin (£10.99)
- Interview by Katinka Blackford Newman
