A major new review of dietary interventions has confirmed traditional plant-heavy diets are the best pathway to good health while some popular, new diets may not be so great for our gut.
The study by Deakin University’s Food and Mood Centre is the most comprehensive synthesis of controlled trials to date, analysing 80 clinical trials across 13 dietary interventions, including Mediterranean and Western diets as well as ketogenic, gluten-free, and plant- and animal-heavy diets.
The study findings, published in The Journal of Translational Medicine, show that diets high in fruits, vegetables and whole grains and low in ultra-processed foods were linked with higher levels of beneficial gut bacteria and better biological markers of health in blood, stool and urine.
Lead author Dr Hajara Aslam, Research Fellow from the Food and Mood Centre, said the findings added to growing knowledge about the way different dietary patterns influence the trillions of microbes living in our gut.
‘These microbes play a vital role in digesting nutrients, regulating the immune system and enabling communication between the gut and the brain.
The diets powering a healthier gut
‘Diets such as the Mediterranean diet, Korean diets, and plant-heavy diets were linked with higher abundance of gut bacteria that produce short-chain fatty acids. These are the primary energy source for cells in the gut and play an important role in maintaining the gut lining, regulating inflammation and keeping harmful bacteria in check,’ Dr Aslam said.
‘These plant-heavy diets were also linked to lower levels of inflammatory markers in blood. That’s a good sign because higher levels of inflammation are often linked to increased health risks.
‘Notably, plant-heavy diets were associated with lower triglycerides and total cholesterol, as well as improved fasting and postprandial glucose levels.
‘In contrast, Western diets – which are typically low in fruit and vegetables and high in salt, fat and ultra-processed foods – were associated with lower levels of short-chain fatty acid–producing bacteria and increased levels of opportunistic bacteria.
‘Opportunistic bacteria are generally harmless to healthy people but take the opportunity to cause infections when the body’s natural defences are down. Western diets were – unsurprisingly – also associated with increased biological markers linked to increased chronic disease risk.
The hidden gut impacts of trending diets
‘There were also interesting findings related to some popular diets. Low FODMAP, ketogenic and gluten-free diets were associated with reduced levels of short-chain fatty acid–producing bacteria.
‘This may be due to these diets often having lower amounts of fermentable fibre which is important for supporting beneficial gut microbes.
‘Despite this reduction in beneficial bacteria, low FODMAP and gluten-free diets were still linked to lower levels of inflammatory markers. This may be because these diets remove the foods that trigger symptoms in people with digestive conditions, helping to calm inflammation in the short term.
‘Overall, our findings highlight the potential of plant-focused, whole food diets to beneficially support the gut microbiota alongside other key biological markers related to health,’ Dr Aslam said.
Co-senior authors Dr Samantha Dawson and Professor Felice Jacka said the review provided some of the clearest evidence to date about what sort of diets beneficially influence the gut microbiota.
‘This review brings together decades of clinical trial research and shows that diet is a powerful and accessible way to influence the gut microbiota and related biological pathways important to health,’ Dr Dawson said.
‘Dietary interventions are a low-risk strategy for modulating the gut microbiota. We now need to do more intervention research to better understand how these changes improve health outcomes for conditions such as heart disease, diabetes and depression.’
‘This study adds to evidence that governments need strong food policies that make healthy diets cheaper, more convenient, and the default choice – policies that are still absent in Australia’, Professor Jacka said. ‘We must urgently confront the “elephant in the room”: the powerful, industrialised food system that drives unhealthy eating patterns.’
This media release was originally created and published by Deakin Media and is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
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