GUT MICROBIOTA AND NUTRITION NEWSLETTER #36
April/May 2022
We hope you are all enjoying the change of season -- some signs of spring in the Northern half of the globe, and a transition to cooler weather in the Southern half!
This month’s curated content related to gut microbiota and diet opens with a review article and a clinical trial that support the benefits of plant-based dietary components on the microbiome. Next comes a review article that examines both human and animal studies that have been completed to date on the non-nutritive sweeteners sucralose and saccharin. For the more clinically oriented folks, we highlight a trial on enteral nutrition and stroke patients and its impact on microbial composition. Finally, we share an intriguing perspective article on glyphosate, coming out of the lab that Natasha currently works in.
Kristina's practice tip shares the latest science around Candida and other gut fungi.
Sending you a big cluster of spring lilacs with your reading!
Natasha & Kristina
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Effects of vegetarian diet-associated nutrients on gut microbiota and intestinal physiology
What accounts for the beneficial health effects of vegetarian diets? These diets are characterized by a higher intake of fibre, plant protein, flavonoids, vitamin A, and calcium, and lower intakes of fat. The nutrient profile of vegetarian diets compared with other diets partially explains the influences of vegetarian diets on the gut microbiome. This review discusses the specific macronutrients (carbohydrates, protein, and fat), micronutrients (vitamin A, calcium), and phytochemicals (polyphenols and phytosterols) present in the vegetarian diet and their influence on the microbial composition. Also reviewed are the microbe-derived metabolites and their interaction with vegetarian diet-associated nutrients, along with their influence on intestinal physiology.
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The effects of the Green-Mediterranean diet on cardiometabolic health are linked to gut microbiome modifications: a randomized controlled trial
This randomized control trial examined the effects of something called the Green-MED diet on cardiometabolic risk factors. The participants followed a Mediterranean-like diet, plus 3–4 cups/day of green tea and 100g/day of frozen Wolffia globosa (Mankai strain) plant frozen cubes as a green shake for dinner. The control group followed healthy dietary guidelines and another group followed the Mediterranean diet (MED) alone. Gut microbiota (from stool samples) was profiled by 16S rRNA gene sequencing. The Green-MED diet induced changes in the gut microbiome composition, with the different diets characterized by distinct taxonomic and functional changes. The MED and Green-MED diets both improved cardiometabolic markers, including the Framingham risk score, body weight, blood pressure, HOMA-IR, and fasting plasma leptin.
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Potential Effects of Sucralose and Saccharin on Gut Microbiota: A Review
Recent studies have reported that sweeteners may have the ability to alter the gut microbiota, with possible negative health effects. Until a few years ago, non-caloric sweeteners were considered metabolically inert and without apparent physiological effects; however, now we know that some of these sweeteners undergo multiple changes in the intestine, interacting with the gut microbiota and thus modifying their metabolites in different regions of the intestine. This review explores potential effects of saccharin and sucralose consumption on gut microbiota composition. Of the 13 animal studies reviewed, 12 studies show that saccharin and sucralose produce time- and dose-dependent changes in the gut microbiota. Some studies highlight how the amount of anaerobic and aerobic bacteria are modified. Others emphasize the effect of sucralose on the Bacteroidetes/Firmicutes ratio and how maternal consumption can affect the offspring. In human studies performed using amounts below the acceptable daily intake and short-term studies, no effects on gut microbiota are found. No long-term studies on humans exist, and sweeteners' health effects is an area for further exploration in humans.
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Effect of enteral nutrition on the intestinal microbiome and risk of death in ischemic stroke patients
This prospective observational study elucidates the impact of enteral nutrition (EN) therapy on the intestinal microbiome in ischemic stroke patients, and identifies the changes to the gut microbiome that may serve as potential prognostic markers. The first part compared the microbiota composition between normal healthy controls (HCs), acute ischemic stroke patients with oral feeding (ON), and acute ischemic stroke patients receiving EN. For most of the taxa that differed between groups, there was a greater decrease in the relative abundance in the EN group compared to the ON group. Akkermansia, Blautia, Faecalibacterium, Dialister, Lachnospira, Prevotella, and Roseburia abundances were significantly lower in the EN group than in the HC group, and those in the ON group were somewhere between the two. The second component of the study evaluated whether the microbiota composition was associated with stroke severity and microbiota-related mortality risk factors in a larger sample of EN patients. Enteral nutrition was associated with an increase in the abundance of beneficial bacteria. The relative abundances of Comamonas and Parvimonas were independently associated with 180-day mortality.
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Is the Use of Glyphosate in Modern Agriculture Resulting in Increased Neuropsychiatric Conditions Through Modulation of the Gut-brain-microbiome Axis?
Glyphosate is one of the most commonly used herbicides and crop desiccants in North America. Upon contact with a weed, glyphosate works by inhibiting a metabolic pathway (Shikimate pathway) involved in synthesizing aromatic amino acids in the roots of plants. The antimicrobial effects of glyphosate residues on ingested foods include killing commensal microbes such as Lactobacillus, Ruminococaeae, and Butyricoccus species, resulting in reductions in critical microbial metabolites that act through the gut-brain-microbiome axis, including indoles, L-glutamate and short-chain fatty acids. This perspective article weighs the evidence for chronic glyphosate exposure on the gut microbiome and the potential consequences on the gut-brain axis, correlated with increased incidence of neuropsychiatric conditions.
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Selected resource
For individuals who are using nutritional therapy for inflammatory bowel disease with the support of their medical team, check out this great website. This resource has a wealth of information comparing different diets, and includes practical advice on foods as well as tips for success.
Find the website here.
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Kristina’s Practice Tip: What you need to know about Candida and other fungi in the gut
Candida, a type of microscopic fungus, is often blamed for all manner of health problems: nausea, bloating, fatigue, mood swaings, and joint pain, among other things. If you search Candida overgrowth online or on social media platforms, you'll find all kinds of purported solutions, including a "Candida Diet" that eliminates sugar, gluten, alcohol, yeast, and certain dairy products on the theory that they feed the fungus and encourage its growth. But what do we really know about the existence of Candida in the gut, and the associated health problems?
Fungi in the gut microbiome
Fungi as microorganisms are much more complex than bacteria and archaea, since they are made up of multiple cells. The fungal members of the microbiome, sometimes called the 'mycobiome', are low in diversity and dominated by Candida as well as Saccharomyces and Malassezia. The mycobiome has not been as well-studied as the bacterial microbiome, and in fact, it's still quite rare for studies to include fungal measurements when they are linking the microbiome to disease. However, we do know that the gut mycobiome of healthy people is usually dominated by Candida albicans so the presence of these fungi per se does not indicate overgrowth. This species is known to have direct interactions with the immune system by inducing Th17 cells.
Gut fungal infections
We've all heard about fungal infections of the nails or skin -- but what about in the gut? Here's where things get interesting. A hundred years ago, gut fungal infections were exceedingly rare. But now they're increasingly common -- for example, in 2012 there was an outbreak in France of fatal infections by a fungus called Saprochaete clavata, which was previously not known to cause disease in humans. Various fungi, including Candida, have become more infectious in recent years, often moving outside the gut into systemic circulation and causing serious infections. In general, more fungal infections are observed in immunocompromised people. Essentially, fungi have become more dangerous to humans over time.
However, it's important to remember that these documented fungal infections involve acute symptoms such as vomiting, fever, or diarrhea. This is different from so-called "fungal overgrowth", which does not cause these symptoms. (See here for an article by gastroenterologist Eamonn Quigley, MD, on common misunderstandings about Candida in the gut.) Doctors currently have no way of diagnosing overgrowth because there are no criteria for what constitutes higher-than-normal levels of gut fungal species. At least one study did correlate higher levels of fungi in the small intestine with unexplained gastrointestinal symptoms, but didn't manage to establish normal limits on gut fungi and didn't prove that the symptoms were actually caused by fungal overgrowth.
Where do we stand?
Currently, we know that fungi are important members of the gut microbiome, which interact with the immune system. Candida and other fungi exist in the gut of healthy people, but they are also associated with infections. These infections can originate in the gut and disseminate to the rest of the body, causing serious illness. The increasing prevalence of fungal infections is indeed worrying, and scientists are exploring whether this is occurring because the fungi themselves have evolved, or because humans (including their microbiomes) have changed in ways that make them more susceptible.
Clinically, there's no accepted standard for identifying fungal overgrowth, and health professionals lack evidence that definitively links gut fungi to various symptoms. So any interventions aimed at decreasing Candida, including dietary protocols, will not be guaranteed to work. With that said, decreasing sugar and starchy, low-fiber foods in the diet can be beneficial overall -- so a client who is highly motivated to try a Candida diet can perhaps be encouraged to reduce those dietary components specifically.
Future scientific studies in this area should aim to show how specific symptoms are caused by fungal overgrowth, and to demonstrate that antifungal protocols can alleviate them.
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