Not so long ago, the five-a-day rule was the only dietary advice we seemed to need. According to the World Health Organisation, eating five daily portions of fruit and vegetables within a balanced diet was key to good health. Now it’s more complicated. ‘Good health’ has been replaced by ‘gut health’ and there’s more talk of fibres, phytochemicals, kefir and kombucha than you can shake a pickle at.
Research from the American and British Gut Project has concluded that the key to a healthy gut – which is vital for overall health – isn’t ‘five a day’ (especially if it’s the same five every day) but the variety of plants in our diet. This changing advice stems from our increasing understanding of the gut microbiome – something few of us would have heard of a decade ago but now attracts huge amounts of scientific research. So what should we really be eating for the happiest, healthiest gut, and why?
Jump to:
- How diet impacts your gut health
- Why your diet should have prebiotic and probiotic foods
- Foods rich in prebiotics
- Foods rich in probiotics
- Best diet for gut health
- What negatively impacts our gut health?
- Why eating with others is good for the gut
- The worst foods for your gut
- Other ways to improve gut health
How diet impacts your gut health
“Good gut health means having a good biodiversity of the gut, a diverse ecosystem of microbes,” says Dr James Kinross, a reader in colorectal surgery and consultant surgeon at Imperial College London and author of Dark Matter: The New Science of the Microbiome. “An important part of that comes from diet. The way I describe it to patients is that the engine in your car is obviously dependent on the fuel you put in it.”
The gut microbiome, the collection of trillions of bacteria, viruses and fungi that live in our digestive tracts, is home to 70 per cent of our immune cells, and also important for heart and brain function, metabolism, weight-management, mental health, clear skin, energy levels – it’s a long list.
These microbes thrive on having a variety of fibres from which to make thousands of different chemicals that interact in unique ways to keep us healthy and do vital jobs like mop up inflammation, defend us from parasites or synthesise neurotransmitters like dopamine and adrenalin. Our diet helps make up this mini personal pharmacy so we want it stocked with the broadest and best range of medicines possible.
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Why your diet should have prebiotic and probiotic foods
“Probiotic bacteria can give our guts regular exposure to live microbes,” says Kate Llewellyn-Waters, an author, nutritionist at KLW Nutrition and resident expert on television programme You Are What You Eat. “This is important as bacteria don’t live for long in our guts, so we should regularly replace them and keep them topped up. At the same time, it’s also important to ‘feed’ the live beneficial bacteria already present in our gut and we can do this by consuming foods with lots of prebiotic fibre. The two work together to maintain a healthy digestive system.”
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Foods rich in prebiotics
“Try to include at least two good food sources of live bacteria in your daily diet,” says Llewellyn-Waters, “and aim for lots of variety.”
- Live natural yogurt
- Kefir
- Sauerkraut
- Kimchi
- Miso
- Tempeh
- Pickled vegetables (fermented pickled rather than vinegar pickled)
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Foods rich in probiotics
- Apples
- Asparagus
- Artichokes
- Bananas
- Broccoli
- Cauliflower
- Fennel
- Flaxseeds
- Garlic
- Legumes
- Leeks
- Oats
- Onions
- Pak choi
- Wheat
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Best diet for gut health
“There is no single make or break food,” says Dr Kinross. “The number one thing you can do beyond any doubt is put more plant-based fibres into your diet.”
Plants high in fibre include lentils, chickpeas, black beans, broccoli, spinach, pistachios, but there are so many more. To fixate on a few is to limit diversity which is critical for gut health.
The evidence from the American and British Gut Project suggests that eating around 30 different plants a week is optimal (above 30 and health benefits begin to plateau.) “If you have seven more grams of plant fibre per day, your risk of cardiovascular disease, obesity, stroke, cancer, everything will fall,” says Dr Kinross. “On top of that, take a little bit of fermented food regularly.
“Other good gut health foods, particularly when it comes to promoting a healthy gut lining, include pumpkin, sweet potatoes, squash, nuts and also chicken stock, as the collagen promotes strong gut lining,” adds Llewellyn-Waters.
Other nutrients vital for optimal gut health which deserve a mention are:
- Wild fish such as wild salmon, avocados, nuts and olive oil which are rich in healthy fats, anti-inflammatory and gut healing.
- Black beans improve gut barrier function and also increase the number of beneficial gut bacteria.
- Antioxidant-rich foods. Most fruits, vegetables and herbs contain antioxidants such as vitamin C, vitamin E, lutein, beta-carotene, flavonoids and lycopene. Blueberries, green leafy vegetables, onion, oregano, turmeric, cumin, basil, ginger, cayenne pepper, dark chocolate (70 per cent minimum cocoa solids), green and white tea are other excellent sources.
- Zinc-rich foods. Zinc is an important mineral for a healthy gut. Researchers from King’s College London have found an association between low zinc intake and inflammatory bowel disease – although if taking zinc supplements, it’s important not to exceed recommended levels. Good natural sources include: poultry, seafood, legumes, lentils and dairy products like cheese and milk.
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What negatively impacts our gut health?
“A diet high in ultra-processed foods, and low in plant-based fibre, is bad for your gut,” explains Dr Kinross. “We don’t yet fully understand the precise mechanisms that make ultra-processed foods so damaging to gut health but it seems that they might directly damage the lining of the gut which is where a lot of our immune system sits.”
However, poor diet is just one driver behind the loss of the diverse ecosystems we need for a healthy microbiome.
“Misuse of antibiotics, drugs and medicines are also key,” says Dr Kinross. “Pollutants play an important part, so does smoking and drinking too much alcohol.”
The way we eat – not just what we eat – also counts. “Having takeaways, eating alone instead of preparing foods yourself with your hands is not good for gut health,” says Dr Kinross.
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Why eating with others is good for the gut
“Sharing meals and eating with friends and family is an important way of maintaining these microbe communities within us. We need other people’s microbes as it ensures that we have diversity and resilience within our own microbiome. It’s a way of seeding it with preferential or helpful microbes; it’s exactly the opposite of catching a cold,” says Dr Kinross.
“Having physical interaction is important, simply because when we prepare food, by touch, by holding cutlery or mixing food with our hands, the microbes from our skin and hands are ultimately transferred. Eating socially, also means you are more likely to have physical contact – shake hands, hug someone or kiss them. This will also share microbes irrespective of diet.
Family sizes are shrinking, real world networks are shrinking, elderly people are isolated – all these things are creating what I would describe as an internal climate crisis – the mass extinction of microbes that we need inside us for optimal health.”
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The worst foods for your gut
- Ultra-processed foods – such as sausage, bacon, pies, biscuits, ice cream. There is much more to learn in order to understand why ultra-processed foods are damaging to gut health, but one theory is that they contain substances – chemical additives and preservatives – that impair microbial life in our gut and create inflammation. Another theory is that the sugars in ultra-processed foods cause harmful bacteria to bloom.
- Fried foods. These tend to be high in harmful fats that could damage the gut microbiome and lead to inflammation.
- Red meat. Research suggests that a diet high in red or processed meat carry a 30 or 40 per cent increased risk of bowel cancer, respectively. A likely cause is the chemicals either naturally found in meat, added during processing or produced when cooking.
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Other ways to improve gut health
Shared meals: “Sharing foods, preparing them yourself and eating them with friends and family is an important way of sharing microbes,” says Dr Kinross. “Our gut microbes are dependent on us being social.
There’s also evidence that eating home-cooked meals as a family improves dietary intake, creates healthier eating habits in young people and reduces obesity in later life.
Prioritise sleep: “The microbes in our gut fluctuate with our circadian rhythms,” says Dr Kinross. “We know that the gut microbiome of night shift workers is very different to those who work regular hours, even when you take into account confounding variables like different diet and nutrition.”
One hypothesis is that sleep deprivation triggers pro-inflammatory changes in the gut microbiome. Research suggests that irregular sleep patterns – even when sleep patterns vary by as little as 90 minutes – are associated with unfavourable alterations in gut microbiome composition.
Regular exercise: “Exercise improves gut health in a number of ways,” notes Dr Kinross. “It improves the profusion of blood flow, regulates appetite and eating patterns and also changes the microbes in the gut.” Both moderate and intense exercise are associated with positive changes in microbiome composition. By allowing more oxygen to reach the bloodstream, exercise creates an environment for good bacteria to flourish. It also reduces the time it takes for food to move through the digestive tract, enabling the gut microbiome to function more efficiently.
Manage stress: “One of the most interesting aspects of the gut is its deep connections with the brain,” says Dr Kinross. “Having good mental health can improve your gut health and having good gut health can improve your mental health – it’s a two way conversation.”
There are many pathways connecting the two. “The first is the immune system. Your gut is such an important determinant of how your immune system functions and 15 per cent of the cells within your brain are immune cells. They talk to each other.”
In addition are well established hormone pathways as well as the vagus nerve, the direct ‘super highway’ that links them. “It seems that bugs in the gut send signals to the brain but equally, when the brain is unhappy – when we’re stressed, anxious, depressed, it can communicate directly with the bugs in the gut and change gut ecology.” Research shows that stress can lead to gastrointestinal disorders such as IBS, ulcers and reflux.
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