Veganuary, a dietary trend that involves going vegan for the month of January, has gained popularity in recent years due to growing interest in plant-based diets. However, there is consistent debate about the benefits and drawbacks of removing animal products entirely from the human diet. We asked Dr Ruairi Robertson, Postdoctoral Research Fellow in the Blizard Institute, about the potential health benefits of a vegan diet in the context of gut health, a growing health trend.
Vegetarianism and veganism are growing dietary patterns in the UK for a variety of reasons including concerns for animal welfare, environmental impacts of livestock farming and both actual and perceived health outcomes attributed to animal foods. Although animal-based foods can form part of a healthy diet, there is growing evidence that diets primarily based around plants can have significant benefits globally for both environmental sustainability and health, by reducing risk of non-communicable diseases such as heart disease and cancer.
Plant-based diets may also have benefits for other shorter-term health outcomes, especially gut health. Gut health is a rapidly growing health focus due to significant scientific advances in the field as well as high rates of gut-related disorders such as inflammatory bowel disease (IBD), colorectal cancer, irritable bowel syndrome (IBS) and other functional gastrointestinal disorders (FGID) in the UK and around the world. The severity, incidence and risk of each of these gut-related disorders are significantly impacted by diet. Growing evidence also suggests that these disorders are significantly influenced by our gut microbiomes – the collection of trillions of bacteria, fungi, viruses and other microorganisms living in our intestines. This interaction between diet, microbiome and gut health is the focus of much exciting scientific research in recent years which may lead to new developments in personalised diets, dietary recommendations or medical treatments for intestinal disorders.
The human gut microbiome is made up of thousands of species of bacteria, archaea, fungi and viruses which collectively form a microbial ecosystem, primarily located in the large intestine, that has a number of implications for human health. The human gut microbiome is essential, for example, for maintaining the integrity of the gut barrier, which provides your body with protection against disease-causing microbes, toxins and other potential invaders. To do this, the gut microbiome communicates with cells within the gut wall, helps to regenerate intestinal mucus and educates immune cells beneath the intestinal wall in order for the immune system to recognise threats. Importantly, the gut microbiome is most effective at carrying out all of these important tasks if it has a diverse array of different species to do so. Gut microbiome diversity is consistently associated with better health outcomes, including lower risk of many chronic diseases.
Diet has a profound impact on the composition and diversity of the gut microbiome. In particular, dietary fibre from plants helps to increase gut microbiome diversity as it is not digested in the upper intestine like other nutrients, and instead travels down to the large intestine where it is digested by the gut microbiome. This digestion of fibre by the gut microbiome has two benefits: firstly, it helps to stimulate the growth of beneficial microbial members of the gut microbiome, allowing them to carry out important functions for the human body; and secondly, the fibre digestion process creates important molecules such as short-chain fatty acids, which can be absorbed into the body and have a number of important health benefits such as strengthening the gut wall and even signalling to the brain to stimulate hunger or satiety hormones.
Dietary fibre is found in all plant-based foods, but is highest in foods such as whole grains, nuts, seeds, bananas, berries, beans and legumes. Many plant-based foods also contain ‘prebiotic’ fibres such as inulin, FOS and GOS, which specifically help to stimulate the growth of particular healthy bacteria in the gut. These foods include artichokes, garlic, asparagus, chicory, leeks and apples. Other plant-based chemicals known as polyphenols are also not digested in the upper intestine and instead are digested by the gut microbiome, which may explain some of their health benefits. Green tea, red grapes, cocoa, flaxseeds, dark berries and a wide variety of herbs and spices are all rich in polyphenols that are digested and metabolised by the gut microbiome. In addition to food containing fibre and polyphenols, fermented foods also help to improve microbiome diversity. Fermented foods such as sauerkraut, kombucha, kimchi and kefir are created through the action of microbes and therefore contains lots of beneficial bacteria and yeasts that benefit the gut microbiome.
Due to the importance of dietary fibre, polyphenols and plant-based fermented foods for the gut microbiome, it is unsurprising that growing research shows that vegetarian and vegan diets have benefits for the gut microbiome and overall gut health. So should we all be doing Veganuary? As always, the answer is not simple. A vegetarian or vegan diet will, by default, increase fibre intake, as fibre is only found in plant-based foods. This is important due to the fact that the UK population doesn’t meet its dietary fibre recommendations. Adults are advised to consume 30g fibre per day, however on average the intake is currently <20g per day. Veganuary may help to kick-start a longer-term diet that contains more dietary fibre, which will ultimately benefit your gut and gut microbiome as well as the environment. However, a rapid increase in dietary fibre can often worsen gut symptoms in those with sensitive guts. In fact, the low-FODMAP diet, which has excellent evidence for reducing symptoms of IBS, actually involves removing a number of foods such as garlic and onion that contain certain fibres, before gradually reintroducing them into the diet. Therefore, if you are prone to a sensitive gut, it may be better to slowly introduce more plant-based foods into your diet, rather than going fully vegan straight away. A ‘plant-based’ diet, that is centred around plants rather than 100% plants, may be a better place to start. If a vegan diet does work for you, make sure you are getting enough vitamin B12, which is found in animal foods, by eating fortified foods or supplements as recommended by the British Dietetic Association.
Veganuary has the potential to benefit your gut by increasing plant-diversity in your diet and increasing fibre intake in addition to providing benefits for environmental sustainability. However, a diet that contains some animal foods is still perfectly healthy for your gut. To improve your diet for gut health, try out some of the tips below.
Dr Ruairi Robertson has a BSc in Human Nutrition and a PhD in Microbiology. His research examines the interaction between diet and the gut microbiome.
He is currently studying the influence of the maternal and infant gut microbiome on early-life growth and infection in the context of child undernutrition. His research is predominantly based in large mother-infant studies in Zimbabwe and Zambia.
Recent publications include:
Dr Ruairi Robertson also hosts The Biomes Podcast, which explores fascinating new developments in our understanding of the human microbiome. In the series, he talks to leading scientific experts around the world about the incredible ways microbes affect your body, from belly to brain.