What Are Prebiotics and Why Do You Need Them?

Gut health is having a moment and for good reason. It is connected everything from mood and focus to inflammation and chronic disease.  

You may have heard of prebiotics, not to be confused with probiotics, but what are they and what do they really do? In this post, I’ll break down what prebiotics are, how they work, and why they matter for your health. In addition, I give examples of common prebiotics found in both foods and supplements, and the ones you want to avoid if you have digestive issues.

What are Prebiotics?

Prebiotics are non-digestible fibers that feed the beneficial bacteria in your gut. They  are not broken down in the small intestine by digestive enzymes, thus, they enter the large intestine intact. Here, the good bacteria “eat”, or ferment (the correct term), the prebiotic fibers.

The key to prebiotics is that they feed the beneficial, not harmful, bacteria; therefore, allowing them to remain viable and proliferate. It’s like growing a new plant, but only you are growing your gut bacteria. Over time, these good bacteria overcrowd the bad (aka pathogenic) bacteria. In addition, the good bacteria get really clever at identifying unwanted intruders and make antimicrobial agents that kill them.

How do Prebiotics Differ from Probiotics?

Prebiotics are different than probiotics. Probiotics are live, active cultures consisting of bacteria that are beneficial to us and are found in foods like yogurt, kefir, kombucha, kimchi, and other fermented foods. (1) Common probiotic taxa include Bifidobacteria and Lactobacillus.

When consuming probiotics from food sources, they must be in high quantities to account for the bacteria that will not survive the harsh pH conditions of the stomach. Colony forming units, or CFUs, are often listed on foods so you know how many live cultures were in the product at the time of manufacture. For example, Lifeway Kefir contains 25-30 billion (yes, that is billion with a B!) CFUs when it was made. Some product labels mention “contains live active cultures” without mentioning quantity and will leave you guessing on how many live bacteria actually make it to your large intestine.

Common Types of Prebiotics

Prebiotics are dietary fibers, but not all fibers are prebiotics. Many plant-based foods naturally contain  prebiotics such as onions, garlic, leeks, artichokes, asparagus, potatoes, wheat, barley, rye, beans, peas, and legumes, bananas, apples, nuts, and seeds, and the list goes on. Many prebiotics are added to foods, like cereals and breads, dairy products, and even confectionery products, to increase the fiber content and improve nutrient quality.  Some examples of prebiotic ingredients found on the food ingredient label include chicory root, inulin, wheat dextrin, psyllium, and galacto- and fructo-oligosaccharides, also known as GOS and FOS.

Resistant starch is also a prebiotic found in bananas, potatoes, beans, legumes and peas (2). Resistant starch part of the starch in starchy foods that is not digested in the small intestine, so it feeds the good bacteria in the large intestine. Interestingly, by cooking and chilling these starchy foods the amount of resistant starch can be increased. The reason is that the starch granule re-compacts during the chilling process to re-form resistant starch. What an easy way to get more prebiotics in your diet! Here is a table of foods with the highest amounts of resistant starch:

Table 1.  Amount of Resistant Starch, a Prebiotic, in Foods Per Serving

Source: Unpublished data from Mindy A Patterson, PhD, RDN and Patterson et al, 2020 J Am Nutr Diet (2)

Tolerability of Prebiotics

Certain prebiotics are not well-tolerated by individuals that have sensitive stomachs, irritable bowel syndrome (IBS), or other gastrointestinal (GI) conditions. The reason is due to the length of the prebiotic fiber. Prebiotics are made of sugar components linked together with some having longer lengths than others. The shorter length prebiotics, such as inulin, FOS, and GOS, are rapidly fermented by the gut microbes causing the rapid release of gas, which leads to bloating, pain, and GI distress. These are typically not well tolerated. However, the longer chain prebiotics, like resistant starch, is slowly broken down by the gut microbes. Due to the slow fermentation of resistant starch, gas is not rapidly made causing improved tolerability. In fact, some prebiotic supplements containing resistant starch, like Renutrin, have received FODMAP Friendly certification, which means that individuals with IBS can tolerate the product.

Why Are Prebiotics Important for Your Health?

Aside from feeding good gut bacteria, prebiotics are known to improve microbial diversity that is often linked to improved health. While scientists do not know how diverse a microbiome should be for optimal benefits, it can be used as a health indicator.

Prebiotics help improve constipation, bloating, and stool consistency allowing for a better and easier “go.”  And because about 70% of our immune system is generated in our gut, prebiotics can boost immune function and reduce infection (3).

Some prebiotics like resistant starch can naturally increase GLP-1 (4) which is a hormone that helps regulate blood sugar and appetite. GLP-1 is released from the gut by compounds that are produced when the gut microbes break down the resistant starch. This hormone  has been shown to improve insulin sensitivity and overall metabolic health. Using prebiotics as a targeted GLP-1 therapy may be a way to alter metabolic health without expensive injections that often cause many unwanted side-effects.

Prebiotics may also have a connection to mood and brain health. Many studies show that prebiotics can reduce the risk of depression, anxiety, and neurodegenerative diseases like dementia and Alzheimer's disease.

How to Add Prebiotics to Your Diet

·       Food first! As a dietitian, I will always recommend natural prebiotic food sources. Many of these foods contain other types of fiber, polyphenols (also beneficial for gut health), and other bioactives to augment the prebiotics benefits.

·       Use cooking and storing methods to naturally increase the prebiotic, resistant starch! Try adding chilled potatoes to salads or adding beans to soups and salads. Or mash them up and use them as a dip!

·       When considering a supplement, always look at the type of prebiotic in the supplement ingredient label. If you have GI issues, you may want to stay clear of the shorter-chain prebiotic fibers.

·       Gradually adding prebiotic fibers to your diet can help ease GI discomfort and allows your body to adjust to the new, but soon amazing changes!

Final Thoughts

Prebiotics are powerful allies for your gut, metabolism, and overall wellness. If obtaining prebiotics through foods, make sure you are intentional and focus on plant-based foods. In addition, if you’re looking to increase your prebiotic intake with a supplement, clinically backed, well-tolerated Renutrin may be a good choice!

(1)    Wastyk HC et al. Gut microbiota targeted diets modulate immune status. 2021 Cell

(2)    Patterson MA et al. Resistant starch content in foods commonly consumed in the United States: A narrative review. 2020 J Acad Nutr Diet

(3)    Wang R et al. Roles of probiotics, prebiotics, and postbiotics in B-cell mediated immune regulation. 2025 J Nutr

(4)    Zang L et al. Metabolic phenotypes and the gut microbiota in response to dietary resistant starch type 2 in normal weight subjects: A RCT. 2019 Sci Rep