Professor Tim Spector revealed he was left “angry and upset” after realising he made a major mistake with his own health.

Tim, the co-founder of nutrition brand Zoe, thought he was a “healthy, knowledgeable doctor” during his medicine career. But he found the advice given to patients about food was ”out-of-date”, “unhelpful” or “unrealistic”.

The 66-year-old says he then started to investigate further and discovered the “advice didn’t stack up”. He cites things like low-fat diets and promoting exercise for weight loss as well as “other nonsense” for his realisation.

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In his new cookbook Food for Life, he wrote: “The more I started digging, the angrier and more upset I became about how misleading this information was. From my medical and physiology background, I knew the advice didn’t stack up – like going on a low-fat diet, counting calories, exercise being fantastic for weight loss and many other bits of nonsense.”

Tim felt that patients were “being misled” by the information given out by the government. He says it made him question his own medical practices.

He added: “We simply hadn’t been taught about nutrition. I thought I was a healthy knowledgeable doctor, but I realised I had got it wrong, and that was quite a shock for me.”

In 2009, Tim says he became aware of the gut microbiome and how it differs between individuals. He says this became apparent during a study of identical twins, in which he found even people with shared DNA can have different gut microbiomes, leading to them developing different diseases.

This he says prompted him to realise the gut could answer “epidemiological” questions he had been trying to answer for 20 years. However, grant funding was hard to get in the UK, so he crossed the Atlantic to continue his work.

He says his research found there were links between the gut microbiome and health issues such as heart disease, obesity, and food allergies. This led Tim to changing his own diet as he trialled different approaches to gut health.

Tim initially went vegan, before realising his food choices impacted on his mood, concentration and energy levels. Gradually he began to eat better and better, noticing a change in his weight too.

He explained: “The food I was eating prior to 2011 was – without me knowing – slowly making me sick. But I came to learn that it was the food I was not eating that was the real problem.”

The health expert says he cut down on ready-to-eat ultra-processed food – most of which was “low-fat and low nutrient” – and instead introduced more fibre and plant diversity into his meals.

The change led to Tim founding Zoe with Jonathan Wolf and George Hadjigeorgiou in 2017. The plan offers its users personalised food scores and advice from nutritional experts.