In a recent review published in the journal Nature Reviews Microbiology, researchers systematically reviewed the impacts of various dietary components and complete dietary regimes on gut microbial health. They analyzed studies on popular dietary regimes, including Mediterranean, vegetarian (plant-based), ketogenic, and Western diets, unraveling how dietary choices at different periods of human developmental stages contribute to metabolic disorders and adult health outcomes.
They further explore the relationships between gut microbial health and subsequent health and disease outcomes. Finally, they highlight progress in diet and gut microbial research, addressing current challenges and areas requiring additional data to improve public health.
Study: The interplay between diet and the gut microbiome: implications for health and disease. Image Credit: CI Photos / Shutterstock
What is the gut microbiome, and how does diet influence its composition and function?
The 'gut microbiome' is the total of all bacteria, viruses, protozoa, and fungi that reside in a host's digestive tract (gut), collectively forming a dynamic and intricate ecosystem that profoundly impacts host health. Recent research increasingly explores the associations between gut microbial health and host welfare outcomes. The findings suggest that gut microbiota composition and relative abundance can substantially alter the host's susceptibility to disease, nutrient metabolism, and even psychological well-being.
Conventional studies predominantly focused on the impacts of antibiotics on gut microbiome health. However, recent research trends are shifting to investigate the impacts of short and long-term dietary choices on microbiome performance. Advances in metagenomic sequencing and artificial intelligence (AI)-assisted analyses have contributed significantly to the latter, bolstering our understanding of the mechanistic and pathophysiological underpinnings of diet-gut microbial interactions and, in turn, facilitating the development of novel diet-centric therapies against common chronic and passing acute health concerns.
Unfortunately, 'one man's food may be another's poison' – a growing body of evidence highlights individual differences in gut microbiome composition and, more importantly, response to dietary interventions. Studies have highlighted how dietary interventions that benefit some geographical populations may display adverse health outcomes in others. In tandem with the global rise in popularity of objectively suboptimal dietary regimes (e.g., the Western diet) and the surge in the consumption of ultra-processed foods, a comprehensive collation and summarization of the vast available literature on the topic is required for both clinicians and the public to better understand what might benefit them (or their patients) best.
The present review aims to address this need while also highlighting current gaps in scientific knowledge and suggesting best practices to fill these gaps for a healthier tomorrow.
The effect of dietary regimes on the gut microbiome
Whole diets are known to have significant positive or negative impacts on gut microbial composition and performance. Some of the most common nutritional regimes include the Mediterranean diet and its derivatives, high-fiber diets, high-protein diets, vegetarian/plant-based diets, ketogenic diets, and the Western diet.
The Mediterranean diet emphasizes the consumption of unprocessed, predominantly plant-based foods, healthy fats, olive oil, and low-to-moderate amounts of dairy products and seafood. Red meats are usually abstained, though in regions wherein red meats are consumed, their proportion in the diet is minimal. Decades of research have established this dietary regime as the 'Gold Standard' in health and preventive medicine, with research into its microbiome influences highlighting an increase in the relative abundance of beneficial bacteria such as Faecalibacterium prausnitzii and Roseburia spp., alongside a reduction in harmful Ruminococcus gnavus, Ruminococcus torques, and Collinsella aerofaciens populations.
The green Mediterranean diet, a medically informed derivative of the Mediterranean diet incorporating a higher plant-based intake than its parent, further displayed increases in Prevotella spp. and reductions in Bifidobacterium spp., thereby contributing to body weight (BW) reductions and improved cardiometabolic outcomes. Similarly, vegetarian/plant-based diets share these benefits, with the high concentration of polyphenols in these diets conferring substantial anti-pathogenic and anti-inflammatory benefits to humans.
High-fiber diets have long been recommended for their long-lasting weight loss benefits, with recent research suggesting that their consumption can reduce the risk of chronic diseases, including cancers and type 2 diabetes. Recently, gut metabolomic patterns have revealed that they promote the abundance of Bifidobacterium spp., Firmicutes, and Lactobacillus spp. notable for their ability to metabolize complex polysaccharides, which contributes to the aforementioned health benefits.
Ketogenic diets are increasingly becoming popular, especially in health-conscious Western youth, despite their origins as an intervention for the treatment of epilepsy. These diets comprise low carbohydrate, high fat, and moderate protein consumption in an effort to emulate (or stimulate) fasting metabolic responses. This forces the body to shift from using carbohydrates to ketones as energy sources. Gut metabolomic research has revealed that these diets are associated with significant decreases in Actinobacteria and Firmicutes populations. Some studies have linked ketogenic diets with decreased host immune response, though this research is often confounding and requires further investigation.
Western diets and diets rich in ultra-processed foods have been observed to be associated with substantial reductions in beneficial microbial population abundances and overall gut diversity. These dietary patterns are known to cause diet-related chronic diseases such as overweight and obesity and their comorbidities (diabetes and cardiovascular diseases) due to an abnormal surge in gut inflammatory markers and reduced host immune response.
Gaps in current research and potential for the future
A vast amount of literature investigating the impacts of diets on gut microbial health focuses on one of a few food items, with only the most common dietary regimes (Mediterranean, vegetarian, and Western) studied on a holistic scale. Furthermore, despite an increasing body of literature on the differences in responses of distinct populations or ethnicities to 'standard' dietary interventions, this area of research remains understudied.
Advances in multi-omics techniques such as metagenomics, metatranscriptomics, metaproteomics, and culturomics will allow for improved identification of population- or even individual-specific responses to different food items and dietary regimes, allowing for the future development of precision nutrition. This emergent field seeks to tailor dietary interventions based on individuals' unique gut microbial compositions or to target specific nutritional or anti-disease requirements.
"By analysing microbiome composition and function, it is possible to identify insufficient or missing dietary components based on specific microbial signatures, as well as select the right probiotics or prebiotics for optimal gut health. Utilizing diet as a form of precision nutrition can be useful in the prevention, treatment and alleviation of disease."
Conclusions
The gut microbiome and its host's dietary habits are intrinsically linked. Alterations in the latter can substantially impact the former, for better or worse. Understanding the mechanistic underpinnings of these associations may allow for the development of personalized dietary recommendations that can help fight disease, improve public health, and even combat psychological disorders in the days ahead. Until then, this review highlights the pros and cons of various popular dietary regimes to arm clinicians and health-conscious individuals with the best foods to incorporate into their grocery lists and researchers with the ideal avenues to achieve a healthier tomorrow.
Ketogenic diet linked to gut microbes and seizure reduction in epileptic children