Written by Hadi Jalali | Published on May 21, 2023 | Last revised on on May 21, 2023

How to Enhance Immunity with Fermented Foods

Throughout our digestive tract, each of us carries 2-3 kg of microorganisms that, along with their genes, strongly affect many aspects of our health. Here, we discuss how to develop and maintain a healthy and diversified gut microbiome to enhance immunity, improve mental health, and regulate inflammation, among other effects.

Benefits

  • Improves digestion and nutrient absorption
  • Improves immune function
  • Regulates inflammation
  • Reduces symptoms of anxiety and depression
  • Reduces the risk of cardiovascular disease, cancer, and type 2 diabetes

My take

I try not to overthink this habit. I usually have several fermented foods on hand, and eat some at every meal:

  • I maintain a water kefir culture, and use the water when I make protein shakes.
  • I make regular batches of fermented buckwheat and oats, which I eat with fruit, nuts, spices and honey for breakfast.
  • I make regular batches of sauerkraut, either using white or red cabbage and adding mustard seeds. I eat this with lunch or dinner. Towards the end of the batch, I start drinking the brine as well, which I find highly palatable. 
  • When I have the patience, I make kombucha, which I drink on some mornings.
  • I regularly buy yogurt and cheese, which I eat once a day.
  • I occasionally make a fermented cashew cream, which I like for breakfast or as dessert.
  • I sometimes buy kimchi (eaten as a side) and unpasteurized miso (mixed into warm water and drunk as soup).

Making these is much more affordable than buying them, not to mention there are many you won’t find in stores, such as fermented oats, buckwheat, or cashews. For me, fermentation is also fun to experiment with. Thanks to my yogurt-maker, which maintains a temperature of about 40°C or 104°F (many programmable appliances are able to do this), experimentation often only takes a day or two rather than three weeks. With regular ferments, I either ferment entirely in the yogurt maker, or use it to jump start a fermentation, then continue for a week or two outside the yogurt-maker on a dark shelf.

The habit: eating fermented foods

Eat a variety of fermented foods, frequently and consistently!

Key points

  • Buy from the refrigerated section.
    Fermented foods contain live active cultures that continue to ferment if they’re not refrigerated—often getting more and more sour over time. Refrigeration slows this down dramatically, but keeps the microorganisms alive. In stores, fermented foods on unrefrigerated shelves (such as sauerkraut or miso) have been pasteurized. They don’t contain beneficial live microorganisms.
  • Try to eat fermented foods with every meal.
    Microbiota (microorganisms in your digestive tract) are continuously made and excreted (through feces).
  • Don’t overthink the serving size.
    The recommended serving size for most fermented foods is 75-200 g, except for miso, where it’s recommended not to exceed 30 g due to its high sodium content.
  • There is no best fermented food. Aim for variety.
    Each fermented food contains its own specific set of microorganisms, with some overlap between different types of fermented foods. The more diversified your gut microbiota, the better. Ideally, try to consume a variety of fermented foods.
  • Feed your gut microbiome with fiber and resistant starch.
    How many microorganisms live in your gut and whether they get excreted depends on your gut chemistry and the food you eat. Eat foods that resist digestion: fiber and resistant starches make it to your intestines and feed your microbiota.
  • Poor sleep and stress both negatively affect the gut microbiome.
    Luckily, we’ve published habits for improving sleep quality and reducing stress.
  • If you overeat fermented foods, expect gas, or in the case of excessive supplementation with probiotics, brain fog.
    Introduce these foods into your diet in small servings, and increase the quantity and frequency over the course of a month to avoid issues.
  • If you plan to cook a fermented food, don’t bother buying it from the refrigerated section.
    Microorganisms in fermented foods generally die off at about 49°C (120°F). Some are more heat resistant, such as lactic acid bacteria, which start to die at about 60°C (140°F). How long they’re exposed to heat is also a factor. Since cooking may kill off any microorganisms present, you can save on cost and buy shelved fermented foods when you plan on cooking them.
  • Avoid antibiotics unless truly necessary.
    Antibiotics negatively impact your gut microbiome, reducing both its diversity and quality, and increasing the risk of reduced immunity.

Tips

  • Here are some common fermented foods you can buy in stores:
    • Yogurt
    • Cheese
    • Milk kefir (liquid or frozen, and can be dairy-free)
    • Kombucha
    • Kimchi
    • Sauerkraut
    • Miso
    • Natto
    • Tempeh
  • Kimchi and sauerkraut add great texture to sandwiches, quesadillas, and rice (or grain) bowls.
  • Microbiota come not only from food, but also through breathing, kissing, and skin contact with people, animals, and the environment—both natural (water, dirt, plants) and manmade.

Do I need this habit?

Maintaining a healthy and diverse gut microbiome is essential for optimal immune function and overall health. Imbalances in the gut microbiome, such as dysbiosis (microbial imbalance) or a reduction in microbial diversity, have been associated with immune disorders, such as allergies, autoimmune diseases, and chronic inflammation. Less dramatically, people with a less diverse microbiome tend to be more sensitive to infections such as the common cold

When we talk about the gut, we mean the 9-meter tube that begins at the mouth and ends at the anus. This is a large collection of organs. Like skin, it interfaces with the outside world, and its importance cannot be overstated.

What are the potential side-effects?

Based on current data, there are minimal adverse effects of consuming fermented foods on human health. Overall, the potential side effects of eating fermented foods are outweighed by the numerous health benefits associated with their consumption. But do consult with your doctor if you have pre-existing medical conditions that you feel may be affected by fermented foods.

The most common side effect of consuming fermented foods is gas. This can happen when you introduce a new fermented food to your diet, or when you eat a larger than usual amount of it at once. To minimize, introduce new fermented foods to your diet gradually. Eat a little each time, and increase the quantity and frequency over several weeks.

One less common side effect of consuming fermented foods is histamine intolerance. Aged cheese, sauerkraut, and fermented meats can contain high levels of histamine. If you are histamine intolerant, you may experience symptoms such as headaches, skin rash, or gastrointestinal discomfort when consuming these foods. Do note that not all fermented foods contain high levels of histamine, and the severity of symptoms can vary among people.

Another less common adverse effect is the risk of contamination with harmful bacteria. The fermentation process in itself is designed to eliminate harmful bacteria. But improper fermentation techniques or contamination during the fermentation process can lead to the growth of pathogenic bacteria. In these cases, the food often looks or smells off. Familiarize yourself with the appearance and smell of each type of fermented food you explore, and you’ll often be able to detect contamination.

What’s the science?

What’s the gut microbiome?

The gut microbiome is composed of trillions of microorganisms (microbiota) that live throughout the gut as well as their genes (metagenome). Together, they strongly impact various body functions.

In an average person, the gut microbiome weighs about 2 to 3 kg. It’s continuously remade and excreted. How many microorganisms, and whether they get excreted or not depends on gut chemistry and foods eaten.

Microbiota come not only from food, but also through breathing, kissing, and skin contact with people, animals, and the environment.

What does the gut microbiome do?
  • It contributes to digestion. Additionally, the genes made by microbiota are involved in the fermentation and digestion of particular nutrients.
  • It makes enzymes for digestion and catalyzing cellular events. This is influenced by the food you eat, and influences the food you can eat. Lacking certain enzymes, for example, would make it difficult to digest certain foods.
  • It affects brain function by facilitating the metabolism of certain neurotransmitters.
  • It affects immune function in several ways:
    • By educating the immune system in its ability to distinguish between harmless organisms and dangerous ones.
    • By maintaining barrier function. It stimulates the production of mucus and tight junction proteins. It prevents the entry of harmful organisms from the gut into the bloodstream. And the presence of beneficial bacteria in the gut helps to suppress the growth of harmful bacteria through competition for nutrients and space.
    • By regulating inflammation. This is partially due to the gut’s effect on immune response, as well as short-chain fatty acids made by microbiota, which have anti-inflammatory effects and modulate the activity of immune cells.
    • By interacting with immune cells in the gut-associated lymphoid tissue and mesenteric lymph nodes. It helps activate immune cells (such as dendritic cells and macrophages) which play an important role in recognizing and presenting antigens to other immune cells, initiating immune responses.
How do the gut and the brain affect each other?

The gut and brain communicate constantly and affect each other’s function. This is called the gut-brain axis.

The gut can signal the brain via the peripheral nervous system (parts of the nervous system outside brain, spinal cord, and retinas) using neurons in the gut—this type of communication is fast.

The gut can also signal the brain by producing neurotransmitters (such as dopamine and serotonin made by your microbiota) and hormones (such as CCK, GLP-1, PYY)—this type of communication is slower. For example, microbiota can make dopamine which enters the bloodstream, and changes the baseline levels of dopamine within the brain.

The brain is able to detect the fullness of the gut using gut neurons that detect its enlargement (or distention). This triggers the brain to suppress the desire to eat or drink more.

How do neurons in the gut affect eating behavior?

They adjust the release of neuromodulators. Neuropod cells in the gut send a signal via a branch of the vagus nerve, to the inferior ganglion of the vagus nerve, and to different stations in the brain stem, eventually causing the release of the neuromodulator dopamine. Dopamine in turn increases craving for the food you’re eating.

What foods are beneficial for the gut microbiome?
  • High fiber foods.
  • Low-sugar fermented foods.
  • Low-dose pre- and pro-biotics on a consistent basis—except in dysbiosis, or cases of long travel, excessive stress, or radical shifts in diet, where high dose probiotics may be helpful.

Research citations

Coming soon!

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