Weight-loss jabs are fine… if we stop eating junk

More people than ever are using weight-loss injections but not enough is being done to improve their diets, Tim Spector, the leading nutrition expert, has warned.

“If we only obsess over weight then we’re missing half the problem,” he said. “Keeping diet preferences the same and still eating harmful, high-processed foods, even if you eat less of them, messes up the gut microbes.”

Spector, a genetic epidemiologist and creator of Zoe, the personalised nutrition app, believes that while weight loss undoubtedly reduces the risk of many diseases, failing to improve our diet “still predisposes people to cancer and mental health issues”.

In October 2024, Wes Streeting, the health secretary, announced the rollout of GLP-1s such as Mounjaro as a measure to address obesity. About 2.5 million people in the UK are now using weight-loss jabs, and British adults have lost an average of about 8kg (1st 3lb) in weight in the past two years, according to a large analysis by the online medical provider Zava.

But Spector is concerned that the NHS and the government are failing to educate patients on nutrition. In Britain, 57 per cent of daily energy intake derives from ultra-processed foods (UPFs), and an even higher proportion (66 per cent) for adolescents.

Spector said: “It is a disgrace. The messaging is still about less calories, less fat, less salt, less sugar. There’s nothing about the quality and satiety of foods which reduce cravings naturally. Unless the two things go together, weight loss medication is going to be a temporary fix and people are going to end up back where they started.”

Spector is in favour of GLP-1 medications but fears the emphasis on weight loss could distract from the importance of gut health: “We shouldn’t be frightened of them but we need to use them properly. We’re not currently using them properly. People are just going to be eating less of the poor-quality food rather than using this as a mass population tool to wean us off craving them.”

Evidence shows that regular or high consumption of UPFs is associated with an increased risk of negative health outcomes, including obesity, type 2 diabetes, cardiovascular disease, poor mental health and various cancers. Emerging research suggests that UPFs may also affect gut health by interacting with the gut microbiome.

A study of 500,000 British patients who accessed Wegovy and Mounjaro weight-loss jabs between September 2023 and November 2025 has found that, collectively, patients have lost 4.2 million kg (more than 660,000st) since Wegovy launched in Britain — an average of about 8kg per person. The findings were almost identical to those from Wegovy and Mounjaro’s own clinical trials.

Last month, the scientific journal Nature published a study of 34,000 Zoe users in which scientists ranked different types of “good” and “bad” bacteria using stool samples to develop a clearer understanding of gut microbes and their links to health. Some experts within the scientific and medical communities have criticised Zoe in the past for its high cost (memberships vary but tests begin at £149), and have expressed scepticism over its clinical relevance for patients with diagnosed illnesses such as irritable bowel syndrome (IBS) or other chronic gut conditions.

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The study showed that if an individual had a cardiometabolic health condition such as type 2 diabetes, they were more likely to have higher numbers of “bad” microbes and lower levels of “good” bacteria than someone without a cardiometabolic condition. They were also more likely to have a higher BMI.

“This means we now have a better understanding of what a healthy gut looks like,” said Spector. “It will help us to see clearer how gut interventions such as fibre supplementation and probiotics help gut bacteria to improve.”

Spector, 67, has previously spoken about his genetic disposition to develop type 2 diabetes with age. Would he take GLP-1 medications to stave it off? “Yes. If a specialist said GLP-1 is what you should be taking, I would. I hope it doesn’t come to that but I think they’re good drugs.”

He is doing all he can to prevent diabetes but fears dementia. His 92-year-old mother, June, was diagnosed with the condition several years ago and last year, Spector took a p-tau 217 Alzheimer’s test. His predicted risk was negligible but results of a full-brain health screening showed early warning signs that could raise his risk of vascular dementia, the second most common form of the condition — the type his mother is likely to have.

“That is one thing I’d love to postpone for as long as possible, so optimising brain health really interests me,” Spector said. “I think there’s lots of things we can do for brain health with nutrition that we’re not even thinking about.”

He now takes folic acid tablets which are said to support brain health by aiding red blood cell formation, reducing inflammation, and improving cognitive function. He recently had blood tests for his Omega-3 levels. “They were borderline being too low which has links with cognitive function which I’m particularly worried about, so now I’m eating anchovies twice per week. I’m always looking for a nutritional way around things rather than a tablet,” he said.

Spector insists he is not a purist when it comes to food. He eats “a Jaffa Cake once every couple of months” and enjoys a panettone at Christmas despite “not really knowing what’s in it”.

“Our body can deal with these things when they’re rare but it can’t deal with them when we’re continuously consuming them,” he said.

“The better your gut health is, the more you can deal with these occasional chemicals which are hard to avoid anyway. We’re not being taught by the government or the NHS about the quality of food that we’re eating.”

Additional reporting by Katie Tarrant