Probiotic Efficacy: What Works Best?

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Probiotic efficacy depends on a variety of factors. Are supplements better than, for example, fermented beverages (e.g. kefir) or foods (e.g. yogurt, sauerkraut)? How many colony forming units (CFUs) should you take? And of which species and strain? In this short review, we provide several considerations relating to probiotic efficacy, dosing, and viability. Here’s what to consider before making your next probiotic purchase.

Related: Health Effects of Probiotics

  1. Different probiotic strains seem to have different physiological effects. One strain may be best for digestive health, another may be best for immune enhancement, while a third may be best to help manage lactose intolerance. Furthermore, each probiotic has optimal dosing ranges. These considerations–optimal strain and dose for a particular indication–have not been fully elucidated in the clinical setting. Dosing in human trials is currently based on animal studies, despite differences in intestinal surface area. Probiotic supplements typically contain at least 1 million CFUs but may have up to 1 trillion CFUs. Furthermore, it is suspected that more severe indications often require specialized strains and larger doses.
  2. Optimal duration of treatment is unknown. The amount of time it would take a given probiotic strain “to colonize, alter the microflora, and have an impact on immune function is unknown,” according to a clinical review. Human studies have shown significant variation in duration of treatment. Generally, probiotic effects will disappear within a few weeks if consumption is stopped. To maintain effect, they need to be taken consistently.
  3. Each probiotic strain may have different survivability in the gastrointestinal tract. Different species of probiotics have different tolerances to the stomach’s digestive conditions (presence of acids and bile salts) and have different growth and nutrition requirements. Few studies have actually examined the survival of probiotic bacteria after administration, and one strain’s survival tendencies should not serve as an indicator for the tendencies of another.
  4. Viable and non-viable bacteria have beneficial effects on human health. Both viable and dead probiotic bacteria have been shown to have immunomodulatory effects, suggesting that other factors (secreted substances, structural components) may have some beneficial effects, as well.
  5. Mode of delivery–yogurt vs. capsule, for example–will affect probiotic efficacy. Different probiotic formulations may have different physiological implications. Ingredients in yogurts are suggested to buffer some of the stomach’s harsh digestive condition and aid in bacterial intestinal passage.
  6. Dosage may change with age. Colonic microflora composition appears to change with age. It is currently unknown if elderly patients should be treated with different probiotics–or smaller doses–than younger patients. Furthermore, there are consideration of safety in immuno-compromised or critically ill individuals, for whom probiotic therapy is typically not recommended.
  7. Effects of long-term supplementation are not well-known. Long-term effects of probiotic therapy are not fully understood and questions of safety, particularly in those with underlying medical conditions, cannot be irrefutably answered.
  8. A combination of probiotic strains may have different effects than a single probiotic strain. It is not currently known if there are synergistic or, perhaps, detrimental effects when probiotic strains are given together.

Related: Can You Overdose on Probiotics?

Given a number of different consideration, there have been inconsistencies in the clinical data, which often makes it hard to draw definitive conclusion and provide specific recommendations. However, understanding where the problems lie also makes it easier to understand where to look and what to consider in an effort to tailor a probiotic to your needs.