Live microbes consumed for health benefits have been delivered in milk products for millennia (See: The Complete History of Yogurt Making). Is this just a historical coincidence, or are fermented dairy products optimal to deliver a probiotic’s benefits? More recently, nutritional supplements (capsules, gummies, powders) and other foods (unfermented milks, juices, chocolate, tea) have been used to deliver probiotics. While we know that probiotic strain and dose can be important, what do we know about the value of consuming one product type over another?
Sanders et al. (2014) discussed this topic at length. A thorough review of the literature on how delivery matrix might affect fecal recovery of a probiotic, probiotic-induced changes in host microbiota, biomarkers and human health endpoints concluded that evidence is spotty and inconclusive. The impact of delivery matrix on different measures of probiotic function has not been investigated in a systematic manner and direct comparisons using the same strains, doses and assessment methods are lacking.
Two recent studies explored the role milk delivery might play in probiotic functionality. The research group, led by Associate Professor Maria Marco at University of California at Davis, asked three questions:
- Does delivery in milk improve a probiotic’s ability to decrease inflammation associated with colitis? (Lee, Yin et al. 2015)
- Does delivery in milk and low-temperature storage (probiotic dairy products are typically refrigerated) have an impact on intestinal survival of a probiotic? (Lee, Tachon et al. 2015)
- Does delivery in milk and low-temperature storage have an impact on a probiotic’s protein expression? (Lee, Tachon et al. 2015)
The studies were done in mouse models, with the probiotic strain L. casei BL23, comparing milk to a nutrient-free buffer (simulating consumption as a nutritional supplement).
The results show that L. casei BL23 works better at attenuating colitis in a mouse model when delivered in milk than in a nutrient free-buffer. Further, a milk-based delivery matrix and low-temperature storage conditions (4 ºC) led to adaptations that improved probiotic survival in the mouse digestive tract. In addition, incubation in milk induced over 200 L. casei proteins. Targeted mutation of some of those proteins led to a ‘less fit’ probiotic. These recent results suggest that dairy may be better for probiotic delivery.
But care should be taken to not over interpret the results, however tempted one may be by the popular press. Some key points:
- Mice are not people. A mouse model enables the researcher to control diet, host genetics and colonizing microbiota, resulting in the lack of many confounding factors that plague studies in humans. But, mice have different physiologies than humans. These models are very informative, but findings must be confirmed in humans.
- These studies were conducted with only one strain. Follow up research that expands the findings to other strains will tell us how widely distributed among probiotic strains these effects are.
- Often with probiotic research, models of disease are studied. But it is not clear what meaning such results have when considering how the research relates to the generally healthy human population. Results in a mouse model of colitis do not necessarily tell us much about results in a healthy human.
- These studies compared milk to a nutrient fee buffer. Is dairy a uniquely beneficial delivery matrix, or do other food substrates bolster probiotic performance?
These studies are noteworthy since they shed light on an important question regarding the importance of the delivery vehicle for probiotic functionality. In a broader context, probiotic function in humans is likely dependent on many factors in addition to delivery matrix, including the individual’s colonizing microbiota, diet, health status, genetics, and the specific probiotic strain and dose. Now we’re one step closer to understanding how to optimize probiotic benefits.