Probiotics and memory: When conclusions can go too far

By Stephen Daniells

- Last updated on GMT

© iStock/SIphotography
© iStock/SIphotography

Related tags Nervous system

A recent rodent study indicated that a combination of probiotics may impair memory in healthy animals – conclusions that industry experts say go ‘a bit too far’, and are at odds with the totality of the evidence.

The data, published in Molecular Psychiatry, tested the VSL#3 product, containing a mixture of Streptococcus thermophilus​ DSM24731, Lactobacillus acidophilus​ DSM24735, L. delbrueckii​ ssp. bulgaricus​ DSM24734, L. paracasei​ DSM24733, L. plantarum​DSM24730, Bifidobacterium longum​ DSM24736, B. infantis​ DSM24737, and B. breve​ DSM24732. Results indicated that an improvement in the microbiota and memory of rats fed junk food, but impaired memory in healthy animals.

In response to the paper’s findings, the scientific advisory board of the International Probiotics Association (IPA) told NutraIngredients-USA: “We are not surprised there is little benefit with a healthy diet in healthy animals. There simply is little room for improvement. The fact that memory performance was reduced may be chance.

“The conclusion in the abstract is grossly exaggerated; talking about subjects (i.e. humans) based on findings in animals. Also in the discussion one study is referred to as ‘proof’ while a recent meta-analysis pointed in the other direction (Wang et al). The study is interesting; but some of the conclusions go a bit too far.”

Systematic review

The Wang et al review cited by the IPA scientists was published in 2016 in the Journal of Neurogastroenterology and Motility. Data from 25 animal studies and 15 human studies were assessed. The interventions mostly used Bifidobacterium​ (eg, B. longum, B. breve​, and B. infantis​) and Lactobacillus​ (eg, L. helveticus​, and L. rhamnosus​), said the authors, with doses between 1 billion and 10 billion colony forming units (CFUs) for two weeks in animals and four weeks in humans.

“Combining all the studies in animals and humans, probiotics appear to have a positive effect in improving central nervous system function,” ​wrote Wang et al.

“According to the qualitative analyses of current studies, we can provisionally draw the conclusion that ​B. longum, B. breve, B. infantis, L. helveticus, L. rhamnosus, L. plantarum, and​ L. casei were most effective in improving CNS function, including psychiatric disease-associated functions (anxiety, depression, mood, stress response) and memory abilities.

“According to the data reviewed, different probiotics exhibited several common effects; however, these effects were strain-dependent and occurred via different pathways at a lower level of the CNS. Thus, more studies are needed for clarify which probiotics target which central biochemical substances and behaviors. In clinical applications, interventions with a probiotics cocktail may have greater effects, because different probiotics may create their effects at the same time through different pathways.”

“More experimental designs in humans should be developed, and more neuroimaging studies should be conducted rather than using only psychological questionnaires or scales. In addition to studies in healthy populations, clinical studies in patients with mental diseases would be worthwhile, because those with gastrointestinal disorders and psychiatric comorbidities, in general, appear to benefit from probiotic interventions.”

Molecular Psychiatry
Received ahead of print, doi: 10.1038/mp.2017.38
“Cafeteria diet and probiotic therapy: Cross-talk among memory, neuroplasticity, serotonin receptors, and gut microbiota in the rat”
Authors: J.E. Beilharz, et al.

Journal of Neurogastroenterology and Motility
Volume 22, Number 4, 2016, doi: 10.5056/jnm16018
“Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review”
Authors: H. Wang et al.

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