The results of a study by researchers at the University of Groningen and University Medical Centre Groningen suggest that high dietary intake of animal products, processed foods, alcohol and sugar, support a gut microbiome that encourages inflammation, while a diet rich in plant-based foods was found to promote gut microbial communities that have the opposite effect.

Reporting their findings in the journal Gut, the team concluded that implementing dietary changes could feasibly help to prevent gut inflammatory processes involved in some chronic diseases. “Modulation of gut microbiota through diets enriched in vegetables, legumes, grains, nuts and fish and a higher intake of plant over animal foods, has a potential to prevent intestinal inflammatory processes at the core of many chronic diseases,” they wrote. “We propose pro-inflammatory and anti-inflammatory mechanisms through which specific foods and dietary patterns could affect inflammatory responses in the gut as a rational basis for designing dietary interventions.”

First author Laura A. Bolte, PhD, and colleagues, described their study and results in a paper titled, “Long-term dietary patterns are associated with pro-inflammatory and anti-inflammatory features of the gut microbiome.”

The composition of the gut microbiome directly affects the balance of pro- and anti-inflammatory responses in the gut. And, as the authors noted, “As microbes thrive on dietary substrates, the question arises whether we can nourish an anti-inflammatory gut ecosystem.” Inflammatory bowel disease (IBD), for example, involves loss of balance between the gut microbiota and the intestinal immune system, they pointed out. But the gut microbial ecosystem may also affect systemic immunity, and an imbalance in the gut microbiome is implicated in a growing number of inflammatory conditions, the researchers further noted. “Beyond the local immune responses, the gut microbiota also affect systemic immune components and are implicated in a growing number of immune-mediated inflammatory diseases (IMIDs), ranging from diabetes to arthritis and systemic lupus erythematosus.”

What isn’t clear is if specific foods and dietary patterns might affect the composition of the gut microbiome and consequently inflammatory responses in the gut. For their reported research, Bolte and colleagues looked at the interplay between usual diet, gut microbes, and intestinal inflammation, in 1425 people, in four cohorts. Participants either had an  inflammatory bowel disease (331 people with Crohn’s disease or ulcerative colitis (UC)), irritable bowel syndrome (IBS; 223 people), or a normal gut (871 individuals). “In this study we aimed to investigate the complex relationship between habitual diet, gut microbiota and intestinal inflammation in humans,” the team wrote. Each person provided a stool sample for microbial analysis and filled in a food frequency questionnaire (FFQ) to quantify average daily nutrient intake. Specific food items were aggregated into 25 food groups, measured in grams per day. The researchers then carried out shotgun metagenomic sequencing to profile each participant’s gut microbial composition and function.

Analysis of the data revealed 38 associations between dietary intake and particular bacterial clusters. In addition, 61 individual foods and nutrients were associated with 61 species of bacteria and 249 metabolic processes across the study participants. Interestingly, the patterns were observed across all groups of study participants, indicating overlaps in diet and gut microbiome signaling between healthy people and those with inflammatory bowel disease or irritable bowel syndrome, suggested the researchers. “We identified significant associations that replicate across patients with Crohn’s disease, ulcerative colitis, irritable bowel syndrome and the general population, implying a potential for microbiome-targeted dietary strategies to alleviate and prevent intestinal inflammation.”

For example, processed foods and animal-derived foods were consistently associated with a higher relative volume of “opportunistic” bacterial species, including certain bacteria belonging to Firmicutes and Ruminococcus sp, and involved pro-inflammatory activity. Plant foods and fish, on the other hand, were associated with ‘friendly’ bacterial species involved in anti-inflammatory activity.

Eating nuts, oily fish, fruit, vegetables and cereals was linked to a higher abundance of bacteria, such as Faecalibacterium sp, which produce short chain fatty acids: these acids help control inflammation and protect the integrity of the cells lining the gut.

Red wine was similarly associated with a higher abundance of several bacteria producing short chain fatty acids. But total alcohol intake, spirits, and sugar were associated with friendly microbial species and functions. Coffee intake was also associated with a higher relative abundance of Oscillibacter sp, while fermented dairy products, such as buttermilk and yoghurt were strongly associated with anti-inflammatory bacteria, such as Bifidobacterium, Lactobacillus, and Enterococcus sp.

Food clusters of breads, legumes such as lentils, peas and chickpeas, fish, and nuts were consistently associated with a lower relative abundance of ‘opportunistic’ bacteria and pro-inflammatory activity. But a fast food cluster of meats, french fries, mayonnaise and soft drinks was associated with a cluster of “unfriendly” Clostridium bolteae, Coprobacillus and Lachnospiraceae bacteria across all study participants. In the absence of fibre, these bacteria turn to the mucus layer of the gut to feed off, leading to an erosion of the integrity of the gut, noted the researchers. “Higher intake of animal foods, processed foods, alcohol and sugar, corresponds to a microbial environment that is characteristic of inflammation, and is associated with higher levels of intestinal inflammatory markers,” they commented.

The team concluded that long-term diets that are enriched in legumes, vegetables, fruits and nuts, with a higher intake of plant over animal foods, a preference for low-fat fermented dairy and fish, and the avoidance of strong alcoholic drinks, processed high-fat meat and soft drinks, could potentially help to prevent intestinal inflammatory processes via the gut microbiome. “Replacement of animal protein by plant protein has a potential to reduce intestinal inflammatory processes by targeting microbial pathways involved,” they added.

The team acknowledged that the observational study wasn’t powered to establish cause, and it’s also not clear how long it takes for gut bacteria to respond to dietary changes. Nevertheless, the scientists noted, “Despite these limitations, we were able to derive dietary patterns that consistently correlate with groups of bacteria and functions known to infer mucosal protection and anti-inflammatory effects … The findings suggest shared responses of the gut microbiota to the diet across patients with [Crohn’s disease, ulcerative colitis, irritable bowel syndrome] and the general population that may be relevant to other disease contexts in which inflammation, gut microbial changes, and nutrition are a common thread.”