The rapid rise in the use of weight-loss injections is not being matched by sufficient efforts to improve diet quality, raising concerns about long-term health outcomes, according to leading nutrition expert Professor Tim Spector.
Spector, a genetic epidemiologist and co-founder of the personalised nutrition app Zoe, warned that an excessive focus on weight loss alone risks overlooking the wider health consequences of poor nutrition. “If we only obsess over weight, then we’re missing half the problem,” he said. “Keeping the same diet preferences and continuing to eat harmful, ultra-processed foods — even in smaller quantities — disrupts gut microbes.”
While acknowledging that weight loss can significantly reduce the risk of many diseases, Spector cautioned that failing to improve diet quality leaves people vulnerable to serious conditions. “You still predispose people to cancer and mental health issues,” he said.
In October 2024, Health Secretary Wes Streeting announced the rollout of GLP-1 medications, including Mounjaro, as part of the government’s strategy to tackle obesity. Since then, the use of weight-loss injections has surged. An estimated 2.5 million people in the UK are now using the drugs, and British adults have lost an average of around 8kg over the past two years, according to analysis by the online medical provider Zava.
Despite these figures, Spector believes the NHS and government are failing to adequately educate patients about nutrition. In the UK, ultra-processed foods (UPFs) account for 57 per cent of daily energy intake among adults, rising to 66 per cent among adolescents.
“It is a disgrace,” Spector said. “The messaging is still about fewer calories, less fat, less salt and less sugar. There’s nothing about food quality or satiety — the things that naturally reduce cravings. Unless diet quality improves alongside medication, weight-loss drugs will only be a temporary fix and people will end up back where they started.”
Spector supports the use of GLP-1 medications but fears their growing popularity could distract from the importance of gut health. “We shouldn’t be frightened of them, but we need to use them properly,” he said. “At the moment, people are simply eating less poor-quality food rather than using these drugs as a tool to reduce cravings for them.”
Scientific evidence increasingly links regular consumption of UPFs with a higher risk of obesity, type 2 diabetes, cardiovascular disease, mental health disorders and several cancers. Emerging research also suggests these foods may damage gut health by disrupting the gut microbiome.
Data from a study of 500,000 British patients who used Wegovy and Mounjaro between September 2023 and November 2025 found that users collectively lost 4.2 million kilograms — more than 660,000 stone — since Wegovy’s launch in the UK. Average weight loss was approximately 8kg per person, closely mirroring results from clinical trials.
Further insights into gut health were published last month in the journal Nature, which analysed stool samples from 34,000 Zoe users. The study ranked “good” and “bad” bacteria to better understand how gut microbes relate to health. While some scientists have previously criticised Zoe for its cost and questioned its clinical relevance for patients with diagnosed gut conditions, the research found clear links between gut bacteria and metabolic health.
Participants with cardiometabolic conditions such as type 2 diabetes were more likely to have higher levels of harmful microbes, fewer beneficial bacteria and higher body mass indexes than healthier individuals. “This gives us a clearer picture of what a healthy gut looks like,” Spector said. “It will also help us understand how interventions like fibre and probiotics can improve gut health.”
Spector, 67, has spoken openly about his genetic risk of developing type 2 diabetes and said he would take GLP-1 medication if advised by a specialist. However, his greater concern is dementia. His mother, now 92, was diagnosed several years ago, and Spector has undergone extensive brain health testing, which revealed early warning signs linked to vascular dementia risk.
“That’s something I want to postpone for as long as possible,” he said. “Optimising brain health really interests me, and nutrition has a far bigger role to play than we currently recognise.”
He now focuses on targeted dietary changes, including boosting omega-3 intake through foods such as anchovies, rather than relying solely on supplements. While he does not avoid treats entirely, Spector stresses moderation. “Our bodies can cope with these foods occasionally,” he said. “They can’t cope when we’re consuming them constantly.”
Ultimately, Spector argues that public health messaging must move beyond calorie reduction to address food quality and gut health. “We’re not being taught by the government or the NHS about the quality of the food we eat,” he said. “That needs to change.”
