What Are Prebiotics?

Sep 19, 2022

By-Julia DeLissio

By-Julia DeLissio

Registered Dietitian and Certified Personal Trainer

Julia graduated from SUNY Oneonta in May of 2015, earning her B.S. in Dietetics. She then spent a few years working in a variety of gyms before matching to her Dietetic Internship. During that time, Julia cultivated a unique skill set from each gym. She began my journey at Crunch, where sh became interested in joint mobility and function. Julia then switched jobs to increase her education on anatomy and physiology, and become a personal trainer.

Julia clocked in over 150 hours of training under One-on-One Physical Therapy, while learning advanced anatomy through Equinox’s EFTI training program. She then relocated to Intoxx on Staten Island, where she single-handedly opened and ran a nutrition education department.

Prebiotics and probiotics are hot right now in the nutrition and wellness space, but does anyone actually know what they are? Do we think it is just a supplement? Do we know their benefits? All of these questions will be answered in part 2 of this 2 part blog series on prebiotics and probiotics!

Now that we have shed some light on probiotics, let’s take a deeper dive into prebiotics.

Prebiotics are food ingredients that help encourage the growth of pre-existing healthy gut bacteria. This may sound bad if you think all bacteria cause illness, however this is a GOOD phenomenon, repopulating healthy populations of bacteria needed for digestion and absorption of nutrients. Since Prebiotics foods are mainly foods that contain a nice serving of dietary fiber, it can be great for your gut health. The increased fiber in the diet can lead to improvements in stool, meaning the individual is less likely to feel constipated, which can be great for those who rely on heavy laxative use. Prebiotics also can lower cholesterol, since soluble fiber can gelatinize in the intestines and reduce cholesterol absorption. The gel-like substance picks up excess cholesterol from being reabsorbed, as shown in the picture below. This interaction between fiber and water can be observed if you were to mix Metamucil with water and wait a moment. You will notice the water will go from a liquid to a semi solid form.

***This is not to say all of your dietary fiber should be from Metamucil, or that Metamucil is a prebiotic. This is to explain and visually show the function of soluble fiber in an applicable scenario.

Common Sources of Prebiotics

Whole Grain/Sprouted Bread

To add to my point above, all prebiotics are fiber, but not all fibers are prebiotic. To be “prebiotic fiber” the fiber must not be able to be broken down or absorbed in the upper GI tract, be fermentable by gut bacteria, and stimulate the growth of populations of good bacterias. Some commonly known prebiotics that you may have seen on a protein or breakfast bar, include inulin and oligo fructose. Since those are more fibers that are added into bars and foods to improve their functionality, I’ve added a list of some common foods you can add into your diet to increase your consumption of prebiotics!

PREBIOTICS: Fermentation in the Gut

The body breaks down dietary fiber into acids, gasses, or alcohol molecules (the fermentation process can be found detailed in the probiotics blog article). These smaller, fragmented compounds provide energy to good bacteria in the colon, creating a habitat where populations of good bacteria can thrive. Common prebiotics include Inulin and Oligofructose, and these ingredients are added to products such as high fiber protein bars to increase the fiber content of the food.

What is the difference between the two?

Inulin is a complicated molecule made up of chains of fructose (essentially fruit sugar) linked by bonds that can’t be broken by human digestion. Inulin is highly fermented by gut bacteria and allows for populations of probiotics to grow.

Oligofructose is a subgroup of inulin. Both help increase bifidobacterium in the gut, which is a type of beneficial gut bacteria. Ideally we will consume most of our dietary fiber from fruits and vegetables, however that may not be practical for some people. You can add in some fortified fiber products, however I do
recommend adding them in slowly if you are not used to having a diet rich in fiber. Start with 10-15g of fiber a day and slowly increase servings of high fiber foods as tolerated. Fiber-fortified foods – e.g. Fiber One products, Metamucil, Quest bars, etc will likely contain chicory root or oligofructose, which are rich in prebiotic fiber. Prebiotics and probiotics are different but similar. I use this analogy to explain the difference to others.

Think of the gut microbiome as a farm.

Prebiotics are the “fertilizer and fuel” : How it grows. Sunlight, water, and fertilizer help the soil maintain its integrity so vegetables can grow. Prebiotics are only found in plants and are not easily digested.

Probiotics are the “crop and seeds”: What is growing. Think of good gut bacteria as what is on the farm, ex. Bifidobacteria is a bacterial colony and carrots are a crop. Probiotics are found in fermented food as opposed to the fiber component of foods. They can be killed by stomach acid, heat, and time, so take them on an empty stomach with water!