Prebiotics Primer: What They Are, Do and Where to Find Them

Prebiotics are basically nutrients for the beneficial microbes in your body, including probiotics. In the past they were defined to be non-digestible carbohydrates which are selectively fermented by gut microbiota, leading to improvements in health
outcomes. Today it is known that more substances than non-digestible carbohydrates can selectively influence proliferation of beneficial microbes.

This webpage is the beginning of a series of pages about prebiotics, with this first page being published in Fall, 2019. Please check back for numerous additions that will be completed over time. This topic is an important one, with research on it exploding, and the huge market for prebiotic supplements rapidly growing. 

The Origin of Prebiotics Research

According to the ISAPP, the International Scientific Association for Probiotics and Prebiotics, the formal study of prebiotics is said to have begun in 1921 when experiments showed that carbohydrates enriched the human microbiota with lactobacilli. The experiments showed that the colon was dominated by anaerobes, bacteria that prefer or require low-to-no oxygen environments, and that certain foods allowed the anaerobes to multiply.

The concept was first defined in 1995 as a "non-digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria already resident in the colon." By doing so, the prebiotic indirectly benefits human and/or animal health.

Over the ensuing years, the concept was refined. In 2004 it was revised to "selectively fermented ingredients that allow specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon host well-being and health."

As of 2017 the ISAPP recommends that the definition be "a substrate that is selectively utilized by host microorganisms conferring a health benefit." This new definition allows for inclusion of substances that may not be fermented, yet still be used to promote a health benefit. It also allows for the sites of the promotion of health benefits to be realized beyond the gastrointestinal tract.

What Types of Substances are Prebiotics?

Strickly speaking, prebiotics are supposed to only selectively stimulate some, but not all, microbial groups, and no pathogenic microbes. They are also supposed to have a distinguishable health benefit. These strict requirements demand scientific randomized, blinded, placebo-controlled trials, just like the requirements for the strict term "probiotics." This strictness favors patented substances and drugs. If you buy a manufactured product labelled as a prebiotic, then, it should have clinical studies to support its use. Substrates that affect composition of the microbiota without involving selective utilization, such as antibiotics, antifungals, minerals, vitamins, and bacteriophages, are not prebiotics.

Nonetheless, realize that not everything works the same in everyone. Prebiotic effects depend on the microbes you have, which may vary from what others have.

Strictness aside, as a nutritionist, I believe that there is room to expand on the concept of the definition, and help people improve their lives, by recommending not only manufactured prebiotic supplements, but also foods and drinks that contain the substances that fit the strict definition of prebiotics, as well as those that have prebiotic-like effects, meaning that they may not necessarily only stimulate a select group of microbes, but yet they still have validated health benefits regardless of which microbe utilizes them. This expansion on the concept is what I will use in the remainder of the articles on prebiotics, as it allows food to be basis of health. As Hippocrates said “Let food be thy medicine and medicine be thy food.”

Prebiotic foods and drinks, then, in the expanded definition, are foods and drinks that contain substrates known to be utilized by host microorganisms that subsequently confer a health benefit on the host.

There are a few broad categories of substrates that are found in foods and drinks that will be explored on this site:

  • Certain fibers, which depends not only on the fiber but on the type of host (that is, human, ruminant, carnivore, etc. This is because ruminants, such as cows, have multiple gastrointestinal organs in which tough fibers are broken down and fermented, but humans only have one stomach that is not designed as a fermentation vessel, and one colon.)
  • Certain substances that may have a demonstrated prebiotic effect in one part of the body, but not in another body part (Xylitol, for example, may help in the oral cavity but not elsewhere. )
  • Certain substances that may have a demonstrated prebiotic effect in one stage of life, but not be relevant in other stages (human breast milk oligosaccharides, for example)
  • Plant polyphenols
  • Certain unsaturated fatty acids

Sources of Prebiotics or Prebiotic-Like Effects

As a  nutritionist, I prefer sources of prebiotics or prebiotic-like substances to be obtained from food. Here are some foods that contain beneficial substances that stimulate beneficial microbes to confer a  health benefit on you:

As I previously mentioned, this topic is a work-in-progress. Please check back often.

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