PROFESSOR TIM SPECTOR: Why I believe changing my diet could've prevented my stroke at 53... and delayed my mother's dementia - and how what I've learned could transform your health in just six weeks

For 15 years, Professor Tim Spector has championed the power of diet to improve our physical health.

The eminent scientist and co-founder of gut health company ZOE has long explored the role of the trillions of tiny bacteria that live in our gut – the gut microbiome – and how small changes to what we eat can have a remarkable impact on everything from our immune system to our heart, our metabolic health and our weight.

But as he tells the Daily Mail, a recent eureka moment unveiled a new discovery. And it was not one he had been expecting.

Two years ago, a study by ZOE found that those who followed Professor Spector's principles for a gut-healthy diet – eating 30 or more plants a week, upping fibre intake and cutting out refined sugar and processed food – not only reaped the health benefits but reported improvements to their mental health.

Within the 18 weeks of the study they found their sleep had improved, they had significantly more energy and they were happier overall.

It could have been dismissed as a chance finding.

But a second ZOE study last year, which encouraged participants to add fermented food such as kimchi, sauerkraut or sourdough to their daily routines, found a similar effect. Thousands of people using the ZOE app to tweak their diets and improve their health were reporting the same thing – eating better was making them feel better.

As Professor Spector, an honorary consulting physician and expert in epidemiology at King's College London, says today: 'We just weren't expecting that. It was a bit of a chance finding in that first study, and not what it had been intended to look at.

'But our findings, alongside other important research elsewhere, has really changed my mind about what is possible with diet.

'We've been treating the body and the brain as separate for far too long.

'Now we understand they're linked. And we have compelling science that suggests by eating well you can not only improve your mood and increase your energy, but potentially improve your brain health in the longer term so you protect yourself against diseases such as dementia. That's really empowering.'

It is as a result of his research at ZOE, and mounting scientific evidence from across the world, that Professor Spector has written a new cookbook, Good Mood Food, which aims to help everyone boost their mood and energy levels by eating a healthy diet full of brain-friendly foods.

In an exclusive new six-week newsletter series launching tomorrow, The Mail on Sunday's readers can discover how to put this research into practice – with the chance to feel happier and healthier within days and potentially, as a bonus, even lose up to a stone in time for Christmas.

The series (see panel on right) will include mood-boosting recipes from Good Mood Food and guide you through a new way of eating that could transform not just your waistline, but how you feel every day.

It'll show you what to put in your shopping basket – and what to leave on the shelves – and how to build delicious, filling meals.

And if weight loss is your goal and you start tomorrow, you could expect to lose up to a stone in time for the festive party season.

 Halfway through, Professor Spector will make a live appearance on dailymail.com to answer readers' questions and talk about his cookbook.

As Christmas approaches he'll reveal how to enjoy your favourite festive foods without undoing all your hard work – and, crucially, how to make these changes stick for life.

This is Professor Spector's most personal work to date. His mother, June, who is in her 90s, is living with vascular dementia, which is caused by the narrowing of small blood vessels inside the brain and is often linked to lifestyle factors, such as smoking or being overweight, or conditions such as high blood pressure and diabetes.

He says: 'Watching her gradual decline made me reflect deeply: could this have been delayed by five or ten years? Probably.

'If, 20 years earlier, we had applied all we know now through lifestyle and medication to reduce her inflammation and unbalanced metabolism, I'm sure her problems could have been delayed and brain ageing slowed down.'

Professor Spector, 68, acknowledges he has an increased risk of dementia because of this family history, and the stroke he suffered in 2011 when he was 53 (a stroke roughly doubles the risk of the degenerative disease developing).

'I know I'm at higher risk,' he says, 'and as many people who have seen dementia first-hand know, dropping dead is much less of a worry than slowly going down that dementia road.

'And every little bit I can do to prevent that is important to me. If I can go on this journey and show other people what I'm doing, hopefully I can show it's not hard. 

'I'm not sacrificing myself. I'm not having an hour of ice baths a day or lifting 50 kilo rocks, as some of the influencers tell you to do. The idea is to make lots of small, intelligent choices throughout a week, and each of those might give you a 1 per cent advantage.'

Those choices are eating a variety of plants – at least 30 different types – every week, adding herbs, nuts, seeds, spices and extra fruit and veg to plates, swapping processed meat for plant-based protein from lentils and beans, and aiming for 30g of fibre a day.

Professor Spector encourages people to avoid ultra-processed packaged foods – although some, such as baked beans and Weetabix, are still allowed – and to add fermented food to meals.

The idea, fundamentally, is that these foods nourish the trillions of bacteria in the gut, and that this in turn nourishes the brain. So what is the evidence behind it all?

There have long been studies that suggest that what we eat affects our health. In particular, the Mediterranean diet – which is similar to the ZOE approach and focuses on whole grains, fruit and vegetables, lean meat and fish, olive oil and beans and lentils – has been found to boost heart health, reduce cholesterol, blood sugar and blood pressure, and help maintain a healthy weight.

Several studies have shown the diet can also reduce the risk of dementia by roughly 18 per cent – the brain benefits because the heart keeps oxygen and nutrients flowing through the delicate network of blood vessels that supply the brain.

Conversely, consuming lots of ultra-processed food – packaged food made with chemical additives that you wouldn't find in a home kitchen – has been linked in numerous studies to low mood and an increased risk of chronic health conditions and diseases such as cancer and dementia.

Work by Professor Spector has shown the state of our gut microbiome influences how we process blood sugar, digest fat, gain weight and respond to infection.

'We now know the brain and the gut communicate through the vagus nerve, which extends from the brainstem to the digestive system,' he says. 

'And while there's still lots that we don't know about the brain, what you eat affects the composition of the microbiome, and in turn that affects the chemical signals that the gut is constantly sending out to the body and to the brain.

'So, for example, if you're eating lots of junk food, that drives inflammation in the gut and causes more harmful bacteria to grow. The message the brain gets is that the body is unwell, or under attack in some way.

'The brain then sends out signals appropriate for the body in that situation – tiredness, fatigue, a lack of pleasure. It's saying, 'You're sick, stay in bed.' Ultimately it's designed to protect the body, but it drives this low mood.'

Conversely, a healthy gut can also trigger the body to produce the brain chemical serotonin – known as the 'happy hormone'.

What made this science more concrete was a 2017 Australian trial on humans which proved that improving gut health through diet could treat depression. 

In the trial, called Smiles, all 67 participants had a diagnosis of moderate or severe depression and all had a 'poor' diet – low in fibre and fruit and vegetables, and a high intake of sweets, processed meats and salty snacks. Many had been ill for some time.

Half were supported to improve their diet, while the other half got social support only.

After 12 weeks, a third of the diet support group were no longer depressed compared with just 8 per cent of the social group.

'This isn't trivial,' Professor Spector says. 'It's a greater cure rate than antidepressants, which studies show can only help around a third of people.

'If our ZOE study is correct, and around half of people see improvements to their mood with diet, then food becomes a better drug than antidepressants.'

Studies show fermented food may have a big role to play, too.

A major study last year that looked at the effect of adding fermented food into diet found improvements to mood and energy, with a dose-dependent effect – the more you consume, the bigger the benefits.

It focused on live yogurt, and brain scans on participants found that consuming it every day increased the volume of the hippocampus – the part of the brain associated with learning and memory. 

In addition, the scientists found there was more connectivity between the hippocampus and the frontal lobe, which is involved in thinking and planning.

It isn't exactly clear why this is, although reducing inflammation is known to be a big part of it.

'Wearing my epidemiology hat, the biggest predictor of cardiovascular death or other problems is actually inflammation rather than high cholesterol or blood pressure,' Professor Spector says.

'There's also a link between inflammation and depression or dementia. One US study showed that if you had five ferments [fermented foods] a day you reduce your blood inflammation markers by 25 per cent – that's as effective as low-dose steroids.'

No studies have yet demonstrated conclusively that a healthy gut microbiome can prevent dementia, as the science remains in its early stages. It is plausible – experimental work suggests that altering the gut microbiome can reduce signs of Alzheimer's in the brains of mice.

Professor Spector acknowledges the lack of conclusive evidence, but says: 'The risk factors for mental health issues and dementia are all very similar, which tells us there must be common ground.

'And in all the studies, you see poor diet there every time.

'We can turn this epidemic of depression and dementia around with an existing treatment – it's called food.

'If we can get Mail readers to sign up to this newsletter and follow my diet principles for a couple of weeks, they'll realise how much better they're feeling. Perhaps they might even carry on for the rest of their lives.

'Then I think we'll have done our job.'