Happy Halloween greetings from the Bear Cave! This week I have a couple of learning opportunities to share with you:

First, I published a guest post on the ​Vibrant Wellness blog​ on the topic of omega-3 fatty acids and muscle health in aging! Protein gets a lot of attention when it comes to muscle, but as we age, careful attention to muscle health involves more than simply increasing protein. In my guest blog, I explore a few different research studies exploring the effects of omega-3 fatty acid supplementation on various markers of muscle health in older adults. Please check it out and share with a friend! (It pairs nicely with ​last newsletter’s​ discussion of mitochondrial health and omega-3 fatty acids, in case you missed that one). There is a ton of great food for thought in these articles on how we can leverage both dietary and supplemental fats to optimize our muscle health as we age.

Next, I was talking with a community member recently about what kind of content is most valuable to Osa readers, and this member told me that she just really wants to know generally what to do to be healthy. At first I balked: But aren’t people tired of general advice? I learned from this community member that many people are just confused about the ocean of often-contradictory and confusing advice available these days. So, while I do find that personalized nutrition and lifestyle intervention is really where the rubber hits the road for the majority, especially those with specific symptoms or diagnoses, it is also true that there are foundational changes anyone can make which can positively impact health, even though how these changes are implemented and what their exact effects or experienced value are will differ among people.

With the goal of providing no-nonsense, evidence-based information that you can use this week we’re going to talk about the gut microbiome, which is considered by functional medicine to be foundational for health and is increasingly being recognized by conventional medicine as a pivotal player in immune function and disease. We’re going to explore an interesting study which compared and contrasted effects of a high fiber diet versus a high fermented food diet in a group of generally healthy adults. I enjoyed reading this study because it reached some surprising and interesting conclusions, and I think it gives us some actionable insights for how we can design or modify our diets to benefit our immune system and overall health via our microbiome. Enjoy!

The Gut Microbiome and the Immune System

First, let’s briefly review the intersection of the gut microbiome and the immune system. The “gut microbiome” (or, simply “microbiome”) refers to the population of bacteria, fungi, archaea, and even some protozoa and viruses that reside in the large intestine (aka the colon), and to a lesser extent in the small intestine, which sits between the stomach and the large intestine and is the major site of nutrient digestion and absorption. These microorganisms (primarily bacteria) ferment fibers, other complex carbohydrates, and even plant polyphenols (think: colors!) that have passed through our small intestine undigested. In fact, many complex carbohydrates in our diets are largely digested not by our own digestive enzymes but by enzymes secreted by the bacteria in our gut.¹ You may also recall that when our gut bacteria are fed by these complex carbohydrates, they produce by-products (“metabolites”) that stimulate the production of satiety hormones including PYY and the now-famous GLP-1 (for more on this topic, please review ​this blog post​ I wrote on the topic). These metabolites also have effects on the immune system, a staggering 80% of which lives in and around our intestinal tract.² This makes sense from an evolutionary perspective: our immune system is our body’s defense forces, so having these forces concentrated where foreign objects are most likely to enter (i.e., through the digestive tract) is a good defensive strategy that promotes survival. (Hopefully, knowing that your immune system is quite literally surveying every bit of food you consume inspires you to take extra care with what you allow in!)

If we have a good density and diversity of healthy bacteria present, our immune system is better equipped to quickly neutralize any threat and to send out the message of “all good here” to the brain. This message is communicated to the brain by way of cytokines, which are the chemical messengers of the immune system. In contrast, when our bacterial population is out of balance, not dense enough, or otherwise unhealthy, the immune system is ill-equipped and threatened, and likewise the intestinal structure itself is also less robust. In this case, the immune cells are more likely to ring the alarm bells by sending out cytokines which promote inflammation–these alarm bells call in the armed forces (i.e., other immune cells) in an attempt to neutralize any perceived threat. In this way, ingested bacteria, various toxins, and even seemingly innocuous foods can provoke a systemic immune response that can have effects which reach throughout the body and can be quite unpredictable and individualized.

Restoring Peace, Bite by Bite

Now that you know that you need an abundance of healthy bacteria to have a healthy immune system, and you know that bacteria eat complex carbohydrates and polyphenols (i.e., the colors in plant foods), you have some idea of what might be a good strategy to repair a damaged microbiome. (And believe me when I saw we’ve ALL got damaged microbiomes). Two food-first strategies to increase the health of the gut microbiome are:

1. Increase complex carbohydrate (i.e., fiber) consumption. It’s important to note that you do not need to be eating a “high carbohydrate” diet to reap the benefits of complex carbohydrates. Remember, the types of carbohydrates that feed our microbiome are not the same type of carbohydrate that increase our blood sugar. We’re talking primarily about the fiber component of plant foods. However, it is also true that not all fibers feed bacteria, and when we are thinking about which foods to choose, we want to give speciall attention to those which contain soluble fiber, which is the kind that dissolves in water. I think of it as the kind that creates a gel. This type of fiber is primarily found in fruits, beans, chia seeds, flax, and seaweed. Remember that polyphenols, the colorful component of plant foods, feed bacteria also, and specific bacteria thrive on specific polyphenols. This is a huge reason why functional practitioners are always telling clients to “eat the rainbow.”
2. Eat fermented foods, which contain bacteria that benefit the gut microenvironment. Traditionally fermented foods include yogurt, kefir, cultured cottage cheese, kombucha, kimchi, miso, sauerkraut, pickles, and other fermented fruits and vegetables. These foods contain a large proportion of lactic acid bacteria from the genera Lactobacillus and Streptococcus but also can contain a variety of other bacteria including some from the genus Bifidobacteria, along with a variety of yeasts. These foods may provide direct and/or indirect benefits derived from the introduction of bacteria and yeast to the intestinal environment, as we’ll see from the discussion of a recent research study….

OK! On to the research!

A group at Stanford conducted an interesting trial comparing the immune effects of a high fiber diet to a high fermented food diet, which was published in the journal Cell with the title “Gut Microbiota-Targeted Diets Modulate Human Immune Status”.³ (They originally called this the “FeFiFo” study for “Fermented and Fiber-rich Food” study, which I thought was cute). This study involved a group of 36 adults who were randomly assigned to one of two groups: a high fiber diet (HiFi) defined as an increase in baseline fiber intake of at least 20 grams (which resulted in ~ 45 grams total fiber daily), or a high fermented foods diet (HiFe) defined as about 6 servings of fermented foods daily*. A serving of fermented food was defined as 6 oz. of kombucha, yogurt, kefir, buttermilk, of kvass; 1/4 cup kimchi, sauerkraut, or other fermented vegetables; 2 oz. of vegetable brine drink. (I am not entirely sure what a “vegetable brine drink” is exactly, but I think it must be the liquid from fermented vegetables, such as the juice from the (traditionally fermented) pickle jar).

*Note that 6 servings of fermented vegetables is indeed A LOT. However, there is not evidence that you need to eat this quantity to positively impact your microbiome. 2-3 servings per day is a more reasonable target for most people.

The study had three active phases: a 4-week “ramp up” phase to acclimate to the sizeable increase in fibrous and fermented foods, a 6-week maintenance phase, and a 4-week “choice” phase, during which time participants could choose to back off a bit on the fiber or ferments to a more sustainable level.

Measured outcomes included measures of microbiome-derived carbohydrate-degrading enzymes (called “CAZymes”), cytokines, and microbiome composition.

What did they find?

Keeping in mind that this was a small study and the participants were generally healthy people, I think that this study still produced findings that provide insights in food-first strategies to consider for optimizing our microbiome health. Here is a summary of the main findings:

1. The HiFi group experienced an increase in the density but not the diversity of their microbes, whereas the HiFe group experienced an increase in diversity but not density. (Density of microbes was estimated by density of microbial proteins in stool samples).
2. The increase in microbial diversity in the HiFe group did not appear to be directly from consumed microbes in the fermented food. The fermented food may have had a largely indirect effect on improving microbial diversity, perhaps by creating an environment recpetive to incorporation of new microbes or a shift in the relative abundance of pre-existing microbes. I thought this was a particularly interesting finding.
3. Despite a lack of increase in microbial diversity, the HiFi group increased their microbiome-encoded CAZymes, which indicates a higher capacity for the microbes to ferment ingested complex carbs–and, as a consequence, create beneficial metabolites such as short-chain fatty acids, which are associated with improved intestinal barrier function as well as improved metabolic health.
4. The HiFe group experienced a decrease in 19 different circulating cytokines, suggesting a lowering of inflammatory activity, whereas there was no signficant change in these cytokines in the HiFi group.
5. In the HiFi group, only those with richer microbial diversity at baseline experienced a lower of inflammation, as measured by signalling in specific immune cells. Highly active immune cells suggests a state of steady immune activiation.

What are the take-home messages?

The key finding for me from this study is that increasing fiber can improve short-chain fatty acid production but is less likely to improve microbial diversity and is also unlikely to improve inflammation, unless the microbial population is already diverse. In contrast, increasing fermented foods in the diet improves microbial diversity and lowers inflammation. As a caveat, it is important to keep in mind that this study is limited (as most studies are) by its relatively short time frame of 14 weeks and its small number of participants. It could be that with more time, fiber could potentially improve diversity, for example.

Action tips*

I think we can use this information to strategize improving our own microbiomes and immune systems. Ideally we will use a combination of fiber and fermented foods. Because a greater microbial diversity appears to decrease inflammation, prioritizing an increase in fermented foods is a wise strategy. If you have trouble tolerating fermented foods (you are not alone!) LOW and SLOW is the mantra. Low can mean something as little as 1 teaspoon of yogurt or kimchi. If you have known yeast sensitivity, it is best to steer clear of yeast-heavy ferments which include kefir, kombucha, and miso until you have yeast in balance.

After successfully introducing fermented foods, gradually increasing soluble fiber (and resistant starch, perhaps: see ​this post​ for more info on resistant starch) can ensure the new microbes have the food they need to thrive. Remember that soluble fiber can be found in fruits, beans, chia seeds, flax seeds, and seaweed. Adding a tablespoon (more or less, as tolerated) of ground flax seeds and/or chia seeds daily is one simple way to easily increase soluble fiber while additionally adding healthy omega-3 fats. Resistant starch is formed by cooking and then cooling carbohydrates such as potatoes, rice, and pasta. I would caution that those with sensitive guts and/or blood sugar dysregulation should keep a close eye on how resistant starch affects them. As with fermented foods, going slow and slow is also a wise strategy for increasing fiber, especially if you have been eating a low-fiber diet.

What if you can’t tolerate ferments or fiber? *

For those with extra sensitive systems, simply increasing polyphenols by eating a large variety of colorful vegetables and fruits daily may be the best strategy. This is appropriate for those following a temporary restrictive eating pattern, such as a personalized elimination diet or autoimmune protocol.

Enjoy the Halloween holiday!

Warmly,

*Disclaimer: This does not constitute medical advice and is for general informational purposes only. Please consult with your healthcare provider to determine whether diet or supplement changes are right for you.

References

1. Kaoutari, A., Armougom, F., Gordon, J. et al. The abundance and variety of carbohydrate-active enzymes in the human gut microbiota. Nat Rev Microbiol 11, 497–504 (2013). https://doi.org/10.1038/nrmicro3050 ​https://pmc.ncbi.nlm.nih.gov/articles/PMC9020749/​
2. Wiertsema, S. P., van Bergenhenegouwen, J., Garssen, J., & Knippels, L. M. J. (2021). The Interplay between the Gut Microbiome and the Immune System in the Context of Infectious Diseases throughout Life and the Role of Nutrition in Optimizing Treatment Strategies. Nutrients, 13(3), 886. https://doi.org/10.3390/nu13030886 ​https://pubmed.ncbi.nlm.nih.gov/33803407/​
3. Wastyk, H. C., Fragiadakis, G. K., Perelman, D., Dahan, D., Merrill, B. D., Yu, F. B., Topf, M., Gonzalez, C. G., Van Treuren, W., Han, S., Robinson, J. L., Elias, J. E., Sonnenburg, E. D., Gardner, C. D., & Sonnenburg, J. L. (2021). Gut-microbiota-targeted diets modulate human immune status. Cell, 184(16), 4137–4153.e14. https://doi.org/10.1016/j.cell.2021.06.019 ​https://pmc.ncbi.nlm.nih.gov/articles/PMC9020749/#F5

Photo credit: Micheile Henderson, at Unsplash