Gut-microbiota-targeted diets modulate human immune status

This small study provided a proof-of-concept that specific 'microbiota-targeted dietary interventions' can rapidly change the gut microbiota and immune system. Using a cutting-edge multi-omics analysis, the researchers tested the effects of two different diets in healthy people. Diet #1 was high in fiber: surprisingly, it did not increase gut microbiota diversity but it did change gut microbial function and changed the activity of the immune system in a way that depended on the baseline microbiota diversity. Diet #2 was high in fermented foods (6 servings / day of yogurt, kefir, kimchi, kombucha, etc.): it both increased gut microbiota diversity and decreased inflammatory markers. Since the second fermented-foods-based diet appeared to have the most beneficial effects, it seems to be a promising way to maintain optimal health and prevent systemic inflammation.

The Gut Microbiome Is Associated with Circulating Dietary Biomarkers of Fruit and Vegetable Intake in a Multiethnic Cohort

Can the gut microbiota reveal exactly how many fruits and vegetables someone has eaten? In this study, concentrations of carotenoid, tocopherol, and retinol were measured in the serum of healthy people, and gut microbiota was analyzed to assess correlations. Some of these biomarkers of fruit and vegetable intake were associated with gut microbiota composition or diversity, but there was no distinct 'signature' for any of them. So while the gut microbiota measures cannot be used as a shorthand for fruit/vegetable intake, fruits and vegetables may have some kind of global effect on gut microbes.

Effects of cat ownership on the gut microbiota of owners

Several studies have found that having a dog in the household shapes your gut microbiota, possibly in a beneficial way. But what if you have a cat? This study analyzed data from the American Gut Project and found that cat owners indeed had differences in gut microbes compared to people who did not own a cat. What’s not clear is whether it’s positive or negative for health -- but as an interesting side note, the cat owners who weighed more (compared to those at an average weight) had gut microbes that appeared to be less affected by the presence of the cat.

Association of ultra-processed food intake with risk of inflammatory bowel disease: prospective cohort study

Prospective cohort studies (which track people & their health through time) are time consuming and expensive, but they're an excellent way to find out the factors that contribute to disease development! This impressive prospective cohort study covered 21 countries, with over 116,000 participants filling out food frequency questionnaires that were validated in their country. Participants were followed for ~9 years to assess dietary differences in those who developed inflammatory bowel disease (IBD). The study found that those who had higher daily servings of ultra-processed foods (sodas, sweets, processed meats, etc.) were more likely to be diagnosed with Crohn's disease or ulcerative colitis. This jives with previous research showing that diet is part of the 'perfect storm' that contributes to IBD development, and highlights the importance of dietary prevention strategies.

Mediterranean Diet to Prevent the Development of Colon Diseases: A Meta-Analysis of Gut Microbiota Studies

So if ultra-processed foods are conducive to IBD (see above), what sort of diet could have preventative effects? This meta-analysis investigated the hypothesis that the Mediterranean diet could be used as a preventative measure for IBD and colon cancer, and that this could be attributable to the gut microbiota changes induced by the diet. They found that the gut microbes in healthy people on a Mediterranean diet pattern tended to be 'anti-inflammatory' -- the opposite of those in people with intestinal disease. This adds to the support for the Mediterranean diet's health promoting effects.

Caloric restriction disrupts the microbiota and colonization resistance

Restricting calories is an evidence-based way to lose weight, but relatively few studies have investigated what happens to the gut microbes during this scenario. In this study, women who were on a calorie-restricted diet (with a first phase that included low-calorie shakes) did lose weight, and they also acquired a unique 'weight loss inducing microbiota'. This seems all good -- but the curious part was that the known pathogen C. difficile also increased, without leading to severe inflammation. This highlights the complex relationship between gut bacteria and positive health outcomes, since sometimes so-called 'bad' bacteria can increase without causing negative health effects.