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Fiber and Probiotics (Why You Need Both)

What is the connection between fiber and probiotics? What about prebiotics, postbiotics and synbiotics?

In this article I will explain all of those terms. Read on to learn why fiber is so important for healthy gut microbes.

Why Probiotics (Microbes) Need Fiber

Probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host.” (1)

As the definition says, you need adequate amounts of these microorganisms in order to get a health benefit. How do you get them? You can take probiotics in pills or other supplements, or you can get them by eating fermented and cultured foods. 

So, probiotics are live organisms, and all live organisms need to eat! Once these microbes take up residence in your gut, where does their food come from?

Microbes eat whatever you put into your digestive system, and don’t actually absorb yourself. The ”good” bacteria like to eat plant fibers. Since you can’t break down and absorb many of the fibers in plants, they are available to feed your little community of microbes.

When you eat, you are not just feeding yourself, you are also feeding your microbiome. If you want to nurture the bacteria that will keep you healthy, you need to feed them the right foods. 

What Are Prebiotics?

The official definition of a prebiotic is “a substrate that is selectively utilized by host microorganisms conferring a health benefit” (2). In other words, it is a substance that your microbes prefer to eat, which in turn gives a health benefit to you, the host. 

The first prebiotic food that many humans get is actually breast milk, which contains oligosaccharides that nourish certain beneficial gut bacteria in the baby. Oligosaccharides are carbohydrates with between 3 and 10 sugar molecules strung together. When you start eating real foods, gut bacteria get their food from plants containing oligosaccharides. Your gut bacteria also love to eat polyphenols, another molecule found in plants (3).  

Benefits of Prebiotic Foods

When your gut microbes ingest all these plant fibers, they make substances that can help to keep your gut healthy. One example is short chain fatty acids, often known as SCFA. Learn more about short chain fatty acids.

All fatty acids are formed in a chain with a backbone of carbon atoms. Short chain fatty acids contain 6 or less carbons in their chain. Butyrate, propionate and acetate have 4, 3 and 2 carbons respectively.

Your body regenerates cells lining the gut more quickly than any other type of cell. These cells slough off and need to be replaced every five days or so. This requires quite a bit of energy. Cells are able to use short chain fatty acids such as butyrate to provide this energy. 

So by feeding your gut microbes, you are actually producing the energy you need to keep a healthy gut lining. 

SCFA also affect gene expression as they signal to turn certain genes on or off. There is growing evidence that they signal the production of proteins that strengthen your immune system (4).  

Short chain fatty acids affect appetite, blood glucose control and production of neurotransmitters (5, 6).  

There are other reasons to keep beneficial gut microbes alive and healthy. They help to maintain the mucus layer in your gut, and prime your immune system to recognize the right kinds of threat. Feeding and populating your gut neighborhood with the healthy microbes crowds out other species that might be harmful.

List of Prebiotic Foods

The foods listed below are some that we know can feed gut bacteria and benefit you, the host. This does not mean they are the only vegetables and fruits that act as prebiotics. Include some of these foods in your meals, but also be sure to eat a variety of other plant-based foods. Variety is the key!

What types of plant fibers are best for feeding the gut? Here are some prebiotic foods to eat regularly:

  • acacia fiber
  • artichoke
  • asparagus
  • apples
  • barley
  • mushrooms
  • onions
  • psyllium
  • seaweed
  • whole grain oats
  • whole wheat

Resistant starches are a category of foods that are resistant to digestion in the small intestine, so they move down into the colon where they can feed your gut microbes. Here are some resistant starches:

  • green bananas and banana peel (Yes, you can actually throw a piece of banana peel into a smoothie.)
  • lentils
  • plantain
  • rolled oats
  • potatoes or rice which have been cooked, and then cooled (think leftover rice or potato salad.)

Variety is Important

It isn’t enough to just say “I eat oatmeal in the morning” and leave it at that. If you want a diverse microbiome with a lot of different types of microbes, you need to feed them a lot of different kinds of foods. 

Pick several different prebiotic foods, and try new ones regularly. Instead of just going for 5 or more servings of vegetables every day, eat 5 or more different types of vegetables. 

What Are Synbiotics?

A synbiotic is a combination of a prebiotic and a probiotic (the microorganism and its food) in one product. This usually refers to a supplement that you take, even though the definition would also fit many fermented foods that you can eat.

Inulin, galacto-oligosaccharides (GOS), fructo-oligosaccharides (FOS), and pectin are examples of prebiotic fibers that are added to probiotic supplements.

It is not enough just to take a synbiotic supplement with one type of fiber. You still need to eat a variety of different plants to keep your microbes thriving and diverse. 

What Are Postbiotics?

According to the International Scientific Association for Probiotics and Prebiotics (ISAPP), a postbiotic is “a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host” (7).

Although the definition is still under hot debate, a postbiotic is basically either a non-viable (dead) microorganism, or parts of that organism, such as cell walls, or substances produced by that organism. This must provide a benefit to the host.

Substances like SCFA produced by organisms in your gut are not technically postbiotics because you didn’t take them, they were produced inside you. However, a supplement containing SCFA might be considered a postbiotic.

Final Thoughts

Probiotics are the microbes you ingest that give you a health benefit. Like all living things, they need to eat. Prebiotics are food for these microbes.

When microbes consume prebiotics they produce substances like short chain fatty acids that can help to keep your gut lining healthy. Short chain fatty acids also affect the production of proteins in the immune system. They affect appetite, blood glucose and production of neurotransmitters.

As they consume prebiotics, gut microbes also help to maintain the mucus layer in your gut and train your immune system to recognize threats.

It is important to eat a wide variety of prebiotic foods. Just like people, different microbes prefer to eat different foods. If you eat a lot of different types of plants, you will grow a more diverse microbiome.

Synbiotics are a combination of a probiotic and a prebiotic, packaged up together in a supplement. This is not a substitute for eating a variety of plant-based foods. 

Postbiotics are non-viable microorganisms or the substances that they produce that benefit the host. They are still being heavily studied, and even the definition is up for debate.

Is gut health on your mind? Let’s talk about the best way for you to move forward.

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