On Probiotics, Prebiotics, and the Gut Microbiome: Benefits, Problems

As you may know, everyone’s gut contains lots of bacteria. This bacterial community consists of many different species, some beneficial, some benign, some potentially harmful.

Though the role of gut bacteria may not be fully understood, we do know quite a bit. For example, we know that by doing fecal transplants in rodents, we’ve learned that we can make skinny rodents fat, and vice versa.

There also hypotheses that suggest the gut microbiome can influence the tightness or “leakiness” of the intestinal-wall cells, which can influence immune function or disfunction, and, thereby, many bodily functions, signs and symptoms.

The bottom line is that a healthy gut — and therefore a healthy body — depends on an appropriate gut microbiome.

One way that we influence the gut microbiome is by taking antibiotics, which may kill or diminish helpful bacterial species. This can make room for less desirable species to become more established and influential. Another way to influence the gut microbiome — this time for the better — is to take probiotics and to eat prebiotics.

Probiotics are bacteria that we can consume either as a supplement or as part of a food. Supplement probiotics are typically capsules. Probiotic foods are those that contain live bacteria including the following:

  • Yogurt (a fermented dairy food)
  • Kefir (a fermented dairy drink)
  • Sauerkraut (a fermented cabbage food)
  • Kim Chee (a fermented cabbage food)

The obvious connection between the probiotic foods is that they’re fermented, which is the process of live bacterial growing in the food, nourished by the natural carbohydrates. Just because you’re consuming what might be a probiotic food (such as those listed above), they are only true probiotics when they contain live bacteria. If you make your own probiotic foods from scratch, then they will contain live bacteria. If you’re buying commercially prepared probiotic foods, carefully read the label, which will list the live bacteria species present.

There is a problem with probiotic supplements in that they don’t always contain the bacteria that they claim. Within the last year or two, researchers at the University of Michigan purchased ten different bottles of probiotics from local stores. When they analyzed the contents, nine of the bottles seemed to contain no live bacteria in their capsules. The tenth bottle had live bacteria in its capsules, but the species wasn’t one of the ones it was supposed to have!

There are professional-grade probiotic brands such as VSL#3, which is available via Internet sellers if not stocked in local stores. If you’re taking a chance on just picking something off the shelf, then buying a refrigerated probiotic supplement at least increases the odds that it may contain live beneficial bacteria.

Prebiotics are foods that when consumed tend to provide food for the bacteria already in your gut. If you want a list of prebiotic foods, simply do an Internet search for that information.

Many people take probiotics (foods or supplements) and eat prebiotics to help support or develop a beneficial, healthy gut microbiome. The idea is that some of the live bacteria survive the trip from mouth to intestine, and thereafter can live and flourish. It is much the same concept as regularly overseeding a lawn to continue to establish new, healthy grass plants and choke out new or existing weeds.

There can be a problem with over consumption of probiotic supplements or foods. Some years ago I was taking a daily probiotic capsule to overseed my own gut microbiome. This went well for a while, but I began to notice daily periods of near nausea. Ultimately, I discovered that when I stopped taking the probiotics, my discomfort ceased. Similarly, more recently I’ve been adding about a half cup (4 fluid ounces) of kefir to my morning oatmeal. I would also consume generous amounts of prebiotics. After doing this for many months, I again experienced bouts of near nausea and abdominal discomfort — not pain exactly, but uncomfortable queasiness and a heavy sensation. I stopped the kefir consumption, and the abdominal discomfort began to ease up.

A constantly-recurring theme in my dietetic practice is that many food related benefits and risks are dose related; too little can be insufficient, too much may be wasteful, harmful or counter productive. I think this is the case for probiotics as well. I think a daily dose while taking antibiotics, for example, will not only be safe but also beneficial. Prolonged daily consumption of probiotics for no specific reason may eventually lead to some minor problems like I experienced. However, occasional routine consumption of probiotics will likely be not only harmless, but also beneficial for most persons.

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Author: Doug Hansford

Registered Dietitian/Nutritionist — trained in university and hospital; certified by the Commission on Dietetic Registration (RDN credential) and by Oxford Biomedical Laboratories (CLT credential). Member of the Academy of Nutrition and Dietetics. Specializing in food sensitivities treating irritable bowel syndrome (IBS), migrane, fibromyalgia, and other conditions related to food sensitivities, which can include asthma, eczema, heartburn/GERD, arthritis, joint pain, chronic fatigue, chronic sinusitis, skin eruptions, and autism/ADD.

Also a former certified personal trainer and part-time lecturer in the department of nutrition and food science at a major research university.