Enhancing our immune response is a worthwhile strategy to protect ourselves against viral infections, whether flu, rhinovirus (common cold), or coronavirus (COVID-19).

I’ve talked previously about how the basic Wheat Belly strategy of wheat/grain elimination reduces metabolic endotoxemia provoked by the gliadin protein that increases intestinal permeability; how wheat/grain elimination and sugar limitation avoids the drop in immune response that follows high blood sugars; how vitamin D restoration restores T-cell immunity against viruses (as well as against autoimmune conditions and cancers).

I’ve also discussed how our L. reuteri yogurt, because it provokes hypothalamic release of oxytocin, may reverse thymic involution of aging, i.e., atrophy of the thymus gland in the chest that is the seat of T-cell immunity. Thymus gland atrophy is responsible for immunosenescence, i.e., loss of immunity with aging. So far, every observation surrounding L. reuteri and oxytocin made in experimental models has held true in humans: accelerated skin healing, augmentation of dermal collage deposition. reduction in appetite (anorexigenic effect), etc. It is therefore likely that this aspect of oxytocin likely applies to humans, too, though not yet fully corroborated. I’ve also discussed how reducing/eliminating another cause of metabolic endotoxemia, SIBO (small intestinal bacterial overgrowth), also reduces body-wide inflammation that impairs immunity.

I’d like to further explore another immune system-building strategy: cultivating the probiotic bacterial species Lactobacillus casei subspecies Shirota. Human clinical trials have demonstrated marked enhancement of the immune response accompanied by reduced susceptibility to respiratory infections and accelerated recovery should infection occur.

Among the effects, both immune-enhancing and otherwise, of administration of L. casei Shirota include:

Above (from Shida 2017) illustrates the reduction in upper respiratory tract infections (URTI, influenza, common cold, others) in men given 100 billion CFUs L. casei Shirota vs. placebo over about 3 months (the magnitude of bacterial counts, by the way, achievable by our own fermentation efforts, below, virtually impossible with commercial products available to us), demonstrating a reduction in infections by about half. (Bolder graph shows the L casei experience.) Not shown is the marked reduction in duration (5.0 vs. 2.8 days per episode), though not in severity.

One potential downside: Many of these studies were funded by the manufacturer of L. casei Shirota, introducing potential financial bias. However, I did not list the studies that demonstrated negative effects such as no reduction in allergic rhinitis and no improvements in blood sugar and measures of insulin resistance (including HbA1c, HOMA, fasting insulin) in obese pre-diabetic males, suggesting that there was no push to only publish positive outcomes. There is, no doubt, potential for bias but the weight of positive evidence that all point in the similar direction of enhancement of the immune response and reduction of inflammatory biomarkers suggest that these are likely genuine findings.

This strain of L. casei is commercially available in the U.S. as the Yakult brand of probiotic beverage, available through selected retailers, only having been introduced on a national basis since 2019. (Here is a store locator.) As with most commercially-prepared beverages, the manufacturer of Yakult does stupid things like use non-fat dairy and add sugar, so I would not recommend consuming Yakult off the shelf. I would instead suggest getting hold of some of the product, then making yogurt (or other fermented product) yourself. And we, of course, do not subscribe to typical yogurt-making rules and instead 1) ferment for extended periods of 24 or more hours and 2) ferment in the presence of prebiotic fibers to increase bacterial counts and richness of the end-product. Each 80 ml (2.7 ounce) bottle (5 servings) contains 6.5 billion CFUs of L. casei; a tablespoon or so provides more than enough to get you started, but may not be enough for effects such as protection from upper respiratory viral infection. Making “yogurt” from it therefore yields a bacterial count amplification system.