A new study has looked at the interactions between "friendly bacteria" commonly found in probiotic supplements and certain micronutrients - with results suggesting many synergistic effects.   Experiments conducted in a laboratory setting found a number of micronutrients were able to enhance the survival and growth of many of the probiotic bacterial strains tested. Probiotics are commonly used to control the growth of less desirable microbes in the gut and it was also found that some micronutrients worked in synergy with the probiotics, exerting their own inhibitory effects on these microbes.

The study was led by Dr. Supriya Yadav from the Agharkar Research Institute, India, and the results are published in the journal Biofactors. The researchers noted the recent trend of probiotic bacteria being added to so called 'functional foods', as well as nutritional supplements, to improve the quantity, digestibility and bioavailability of the nutrients they contain. For example, probiotics have been shown to enhance the bioavailability of the vital minerals, zinc and iron. 
 

According to Yadav and colleagues the reverse relationship - the effects of micronutrients on the growth of probiotic bacteria -  had not been investigated. The researchers therefore designed experiements to determine the influence of selected micronutrients and antinutrients (phytochemicals such as phytic acid and oxalic acid which inhibit mineral absorption) on the growth of selected probiotic strains. 

Eight nutrients and antinutrients were selected -  zinc sulphate, zinc carbonate, ferrous sulphate, ferric citrate, quercetin, gallic acid, phytic acid, and oxalic acid. Their effects on the growth of Lactobacillus acidophilus, Lactobacillus plantarum, Bifidobacterium longum, Bifidobacterium bifidum, one commercially available multistrain probiotic formulation (containing six Lactobacilli and two Bifidobacterial cultures), as well as commensal E. coli, were monitored individually.

The researchers reported that quercetin and zinc sulphate significantly enhanced the growth of Lactobacillus acidophilus and the multistrain formula, but that the other micronutrients had no discernible effect.

Oxalic acid, generally considered an antinutrient, also had positive effects on L. acidophilus and the multistrain formula, with no effect on growth of other probiotics.  

Additionally zinc sulphate, ferrous sulphate, quercetin, and oxalic acid were found to significantly inhibit the growth of E. coli. Whether this is a good or bad thing is open to debate as some strains of E.coli have been shown to have beneficial health effects (see E. coli-containing probiotic Mutaflor).

Finally, the researchers determined that phytic acid had an inhibitory effect on L. plantarum and both strains of Bifidobacteria, but did not affect growth of the other probiotics one way or the other.

Yadav and colleagues conclude that the inclusion of micronutrients and phytochemicals such as zinc sulphate, iron sulphate, and quercetin in probiotic formulas may enhance probiotic bacterial growth and the therapeutic effect of such products. Their results would also suggest that those supplementing with certain probiotic strains might wish to take these supplements at times away from foods high in phytic acid, or even avoid such foods altogether. Foods with a high phytic acid content include seeds, nuts, grains and pulses.

It should be noted however that this research was preliminary and to obtain a better idea of how probiotics and micronutrients interact there is a need for human studies.

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