Back in the 2010s, celebrating bodies of all sizes was the rage. People magazine featured plus-size model Tess Holliday on the cover after her 2013 Instagram campaign #EffYourBeautyStandards went viral.
Meghan Trainor’s pop hit ‘All About That Bass’ shared her momma’s advice to not worry about your size, while Lizzo celebrated her own body in her song ‘Juice’.
But now we live in a post-Ozempic world. Meghan Trainor and Lizzo have both lost weight, with Trainor citing Mounjaro (an Ozempic-like drug) for her transformation.
Then there's SkinnyTok. More than half a million TikToks have been posted under the hashtag, which the US National Alliance for Eating Disorders claims "[glorifies] thinness and vilifies weight gain".
Thanks to injectable weight loss drugs such as Ozempic, Wegovy and Mounjaro, significant weight loss is now more achievable than ever – especially for those who can afford to pay for it.
For many health experts, the new drugs are a renowned success. For the first time in decades, US obesity rates are declining — and some scientists believe these medications may be a reason why.
But not everyone sees weight loss as an automatic win. Some researchers argue that body weight is more complex than a disease to be eliminated – and that focusing narrowly on weight loss can sometimes backfire. Rather than treating fat as the enemy, they say it’s time to rethink its role in the body.
In the words of Prof Francesco Rubino, Chair of Metabolic and Bariatric Surgery at King’s College London: “Your fat tissue is not all evil. It serves a purpose.”
Why fat matters
We tend to think of fat tissue as a bad thing – perhaps because a lot of us have a lot of it – but, as Rubino points out, “The physiological function of the fat tissue is vital.”
Our layers of fat protect our bones from breaking – so, older people (especially women) with less fat tissue might be more at risk of falls and fractures than those with a bit more padding.
But our fat tissue also stores energy, so it can provide our bodies with some extra fuel when we’re not getting enough from our diets.
“Energy is what keeps us going,” says Rubino. “If you have some spare for when you need it, it’s not too bad.”
So, he explains, our bodies might benefit from a little extra weight when trying to recover from illness or injury – a phenomenon known as the overweight paradox.
“When you have to fend off a disease, then having a little bit of extra fat is actually not bad for you,” says Rubino.
In fact, he continues, some studies have shown that if you have a major operation, if you go into intensive care, if you go through cancer treatment – you tend to “fare better” with a little extra weight.
But Rubino clarifies that this advantage doesn’t necessarily apply to people whose excess weight is, itself, damaging their health.
For instance, some people may experience joint pain – especially on the knees, hips and back – because of extra strain caused by their weight and posture.
Fat accumulation around the torso can restrict lung capacity, making breathing difficult, and the added energy that’s needed to maintain a larger body can lead to persistent tiredness.
That’s without considering the risk of other diseases, such as type 2 diabetes, heart disease, liver disease, and more.
“As with everything in our body and in medicine, sometimes even a physiological process that is meant to be protective can end up causing harm,” says Rubino.
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When you should avoid losing weight
So, if you’re preparing for surgery or to undergo disease treatment, now might not be the best time to go on a strict weight loss diet. The same applies to other groups of people who could benefit from building their energy stores.
For instance, most pregnant people should expect to gain a significant amount of extra weight to support their growing foetus, not attempt to lose it.
“The baby is like a parasite in the body that will be sucking up all your nutrients,” explains Dr Dimitrios Koutoukidis, Nuffield dietitian and associate professor at the University of Oxford.
“In order to make sure that it develops fully, you want to make sure that you have enough calories in your body.”
Koutoukidis also emphasises that people without excess fat have no medical reason to pursue weight loss.
“If somebody is underweight to start with, they definitely should not be losing weight," he says. "And if they’re in the healthy weight range, then they probably shouldn’t lose weight.”
Is obesity a disease?
It’s easy to understand why a slim person might not need to lose weight. But when it comes to people in larger bodies, many of us assume that weight loss is always the healthiest goal. Rubino claims that’s not necessarily true.
“All the evidence tells us that the sickness of an individual is not related to weight itself,” he says. “You can have modest obesity and very significant health impacts, and vice versa.”
In medical settings, doctors tend to recommend weight loss to people over a certain body mass index (BMI) – meaning their weight is higher than what’s considered average for their height.
However, the BMI system isn’t perfect. Far from it. It doesn’t take into account a person’s muscle mass, blood sugar responses or heart health.
To discover the true relationship between weight and health, Rubino led a Lancet Commission, published in January 2025, that set out to distinguish between different types of obesity.
“Obesity cannot be labelled in a uniform way,” says Rubino. “The question is: is the individual in front of me having an illness here and now? And if so, what kind of illness is it?”
The commission made the distinction between approaching obesity as a disease – called ‘clinical obesity’ – and obesity as a risk factor for future poor health, called ‘preclinical obesity’.
“If obesity is a disease, it must be able to affect your organs – your heart, your liver, your kidneys – in ways that don’t require another disease to happen,” explains Rubino.
“If there is no evidence of any of those organs malfunctioning, it’s hard to say that’s a disease. Any disease must cause illness.”
So, if your excess weight is causing ill-health – either you feel unwell, or your doctor can recognise signs of ill health in your body – then you could be prescribed a weight-loss intervention such as a new diet, drug or surgery, to treat your obesity.
But if your extra weight doesn’t seem to be damaging your health, then your obesity probably isn’t a disease.
That’s not to say you should do nothing. Extra weight can put you at risk of developing clinical obesity or related diseases – such as type 2 diabetes or heart disease – later down the line.
However, you may decide that the benefits of weight loss are not worth the potential risks.
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Shedding pounds fast can come with side effects
Regardless of whether someone is carrying a little extra weight or has diagnosed clinical obesity, certain weight-loss methods can come with serious side effects – especially when the sole focus is on losing weight, rather than improving overall health.
“We normally think we should prescribe weight loss, but we can’t,” says Rubino. “Weight loss should be the consequence.”
As a bariatric surgeon, Rubino operates on people with obesity to physically alter their digestive system – for instance, by reducing the size of the stomach – so they feel fuller and eat less.
But weight-loss surgeries are major operations that can lead to a range of complications, from nausea and pain, all the way to blood clots and stomach leaks.
Then there are GLP-1 medications like Ozempic or Wegovy: injectable drugs that mimic fullness hormones, slow digestion and improve blood sugar regulation, encouraging people to eat less.
Most people on those drugs experience side effects, which may include nausea, vomiting, diarrhoea, constipation, nutritional deficiencies, and in extreme cases, stomach paralysis.
For those who opt for traditional diet-and-exercise methods, Koutoukidis says: “If the diet is sensible in quality, then people can be relatively reassured that weight loss can be a safe endeavour most of the time.”
However, get the diet wrong – such as with a low-calorie, nutrient-poor crash diet – and you may develop nutritional deficiencies, which could lead to bone loss, muscle wastage or fatigue.
And Koutoukidis explains that this could be a problem even if you eat enough vitamins and minerals, or take supplements alongside your diet.
“You need a set amount of protein and fat to function normally,” says Koutoukidis. “So, your muscles might waste, and you might feel much weaker. Losing muscle wouldn’t be beneficial to your long-term health.”
The mental toll of weight loss
As if the physical side effects weren’t challenging enough, trying to lose weight can come with a significant mental toll – particularly if the person feels they aren’t losing weight as quickly as they would like.
“We can’t fine-tune the weight loss we want,” says Rubino. “It depends on the interaction of the drug or the surgery with that particular individual.”
He explains that some of his patients blame themselves when they are unable to reach their desired weight loss.
“I have people coming to my clinic crying because they think, ‘I got surgery, and I didn’t lose as much weight as others,’” says Rubino.
“They think there is something wrong with their moral fabric, or their mind, which is not true. It’s just the way biology works.”
He says that the majority of his patients never reach their ideal weight, even after undergoing weight-loss surgery – but “they become incredibly healthy.”
“So, the question is, should these people lose more weight?” continues Rubino. “I think the answer is no. There’s no advantage of losing that weight, and whatever you do to push it farther would have dubious benefits.”
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