The diet myth: Go with your gut - changing the way we think about food 

Focusing on gut health and the microbiome is more useful than focusing on diet and calories and weighing scales

A leading scientist says calorie counting can lead to weight gain and general ill health in the long term.

A leading scientist says calorie counting can lead to weight gain and general ill health in the long term.

Tim Spector, professor of genetic epidemiology at King’s College London, argues that it is what is inside our gut that counts. 

“It’s that diversity of gut microbes that gives you a diversity of chemicals, a healthier immune system and better metabolism,” he says.

“Once people start seeing there is a link between the food we eat, our microbes and our immune system, that changes the way we think about food. It’s not just fuel — it really is changing the way our body works.”

The Diet Myth author says the micro-organisms in our guts are like an inner chemical plant, producing thousands of gut hormones and chemicals that not only break down food and use the contents to aid digestion but also send constant messages to our immune system. These organisms also produce brain chemicals, such as serotonin, as well as additional molecules that control how our bodies change food into energy.

Tim Spector, professor of genetic epidemiology at King’s College London. 

To do this microbes need about 30g of fibre a day. Good sources of fibre include wholemeal cereals and bread, jacket potatoes, wholewheat pasta and rice, vegetables, and fruit. With the average daily intake of fibre in Ireland much lower (about 14g), this may be why modern low-fibre, ultra-processed diets are so problematic for human gut health.

Internationally acclaimed author of Metabolical (2021), Robert Lustig agrees. The result of all this processed food is that “our livers are stuffed from the sugar our bodies turn into fat — we’ve literally turned ourselves into foie gras,” he says. “Our guts used to be full of beneficial intestinal bacteria that munched on fibre and kept everything in our bodies [in excellent order],” he says. “Now that food has been stripped of its fibre, and those bacteria get so hungry they eat the mucin barrier (the gelatinous coating that lines the intestinal wall) off our intestinal cells, setting us up for inflammation and leaky gut.”

Fibre is vital

Lustig says fibre is the key ingredient for a healthy gut. It has the dual advantage of slowing the absorption of sugars in the duodenum and preventing the liver from turning excess energy into fat — in turn preventing insulin resistance and chronic metabolic disease. The fibre then makes its way to the large intestine, where it can become food for the gut bacteria, which is essential for a healthy microbiome.

“Fibre is perhaps the single most important nutrient for health because it both protects the liver and feeds the gut,” adds Lustig.

Foods high in fibre include broccoli, lentils and other beans, berries, apples, pears and porridge.

Spector says a healthy microbiome can be achieved by consuming a diverse and predominantly plant-based diet that is free from highly processed foods. He recommends plants that are “rich in chemicals called polyphenols — generally ones with strong tastes and colours, slight bitterness, thick skins”. Or basically, the opposite of iceberg lettuce. Think instead of purple carrots, grapes that are sour and bitter, red lettuce, asparagus, spinach, and broccoli.

Other foods that support your gut microbiome include green tea, extra virgin olive oil, herbs, and spices – plus a small amount of dark chocolate. Fermented foods — kefir, kombucha, kimchi and kraut — as well as cheese and yoghurt act as fertilisers for resident gut bacteria.

If this all sounds familiar that’s because it is. It is very similar to a Mediterranean diet — high in fruits, vegetables, wholegrains and containing less meat and dairy products than a typical western diet.

The microbiome is also suggested to influence the body’s response to infection. Spector is best known for his work on the ZOE Covid symptom study (2020) which found that people who consumed a greater diversity of plant-based foods appeared to be less susceptible to catching Covid-19 or becoming seriously ill from it. In his view, the immune system is compromised if it doesn’t have a good microbiome controlling it.

“I don’t think eating for our microbiomes would stop pandemics, but I think it could make everyone less ill if they got infected.”

Fresh veg are essential for good gut health

Mental health

Poor gut health has been identified as a key factor in mental health. There is a growing consensus that depression may be linked to elevated levels of inflammation and that having the right gut microbes can counter this because they secrete a range of chemicals that keep inflammation in check as well as potentially having a direct mood-altering effect. Certain microbes help to produce serotonin — the same chemical increased by antidepressants.

UCC neuroscientist Prof John Cryan has been one of the most vocal proponents of a microbiome–brain connection. A study with two large groups of Europeans (2019) found that several species of gut bacteria are missing in people with depression, adding to the evidence that gut bacteria can influence mood.

Mounting research is reporting the impact even a short course of antibiotics can have on the microbiome which is one of the reasons why they should only be used when there is a clear indication of a bacterial infection.

Perhaps we should focus more on foods rich in fibre and polyphenols and less on diets, calories and weighing scales. Eating this way could also boost your mood.

• Dr Catherine Conlon is a Cork public health doctor and safefood’s former director of human health and nutrition