The various beneficial effects of soybeans, which are rich in phytochemicals, have received much attention because of increasing health awareness. Soy milk that has been fermented using lactic acid bacteria has been used to prepare cheese-like products, tofu (bean-curd), and yogurt-type products. However, the distinct odor of soybeans has limited the acceptance of such foods, particularly in Western countries. In Japan, while tofu and soy milk have long been habitually consumed, the development of novel, palatable food products has not been easy. The unpleasant odor of soy milk and the absorption efficiency for isoflavones can be improved using a recently developed fermented soy milk beverage. Cancer has been the leading cause of death, and breast cancer is the most common malignancy among women. The most common type of breast cancer is estrogen-dependent, and the anti-estrogenic effects of isoflavones are known. The present review focuses on the characteristics of soy milk fermented using probiotics, an epidemiological study examining the incidence of breast cancer and soy isoflavone consumption, and a non-clinical study examining breast cancer prevention using fermented soy milk beverage.

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A double-blind, placebo-controlled, randomized trial was conducted to investigate the beneficial effect of probiotic and prebiotic fermented milk on the skin of healthy adult women. Forty healthy Japanese adult female volunteers with healthy skin randomly received either a bottle of probiotic and prebiotic fermented milk containing Bifidobacterium breve strain Yakult and galacto-oligosaccharides (GOS) (active group) or a non-fermented placebo milk containing neither probiotics nor GOS (placebo group) daily for 4 weeks. Before and after intake, hydration levels and cathepsin L-like activity in the stratum corneum and phenol levels in the serum and urine were determined. After intake, the hydration level of the stratum corneum decreased significantly in only the placebo group and was significantly lower than in the active group (p=0.031). Cathepsin L-like activity, an indicator of keratinocyte differentiation, was significantly increased in the active group (p=0.027). Serum and urine phenol levels decreased significantly in the active group (p=0.014, p=0.002, respectively), and serum phenol levels were significantly lower in the active group compared with the placebo group (p=0.006). The consecutive intake of probiotic and prebiotic fermented milk can benefit skin condition without dryness and decrease the levels of phenol production by gut bacteria in healthy adult women.

Few studies have examined the effects of smoking habit, the frequency of alcohol drinking, exercise, and fermented milk consumption on defecatory symptoms and gut microbiota composition, and particularly their interactive effects. We examined the effect of these lifestyle factors on bowel movements and gut microbiota composition in 366 healthy Japanese adults by analysis of covariance. Smoking did not affect defecatory symptoms but was negatively correlated with total bacteria and Enterococcus counts. Drinking frequency was significantly positively correlated with a feeling of incomplete evacuation and counts of the Bacteroides fragilis group and Acidaminococcus groups. Exercise frequency tended to be negatively correlated with the Bristol Stool Form Scale score and was significantly negatively correlated with the counts of Enterobacteriaceae and positively correlated with the Prevotella counts in the faeces. The frequency of fermented milk consumption was not significant but tended to be positively correlated with stool frequency. The frequency of fermented milk consumption was significantly positively correlated with the counts of the Atopobium cluster, Eubacterium cylindroides group, Acidaminococcus group, Clostridium ramosum subgroup, and Lactobacillus in the faeces. The frequency of consumption of probiotic Lactobacillus casei-containing fermented milk was significantly positively correlated with stool frequency. The counts of probiotic Lactobacillus casei in the stool was positively correlated with the counts of Bifidobacterium and total Lactobacillus. These results suggest that smoking, alcohol drinking, exercise, and consumption of fermented milk, particularly containing probiotic L. casei, differently affect bowel movements and gut microbiota composition in healthy Japanese adults.

Several clinical studies have shown that isoflavones and Lactobacillus casei Shirota (LcS) have beneficial effects on skin condition and the gut microbiota, respectively. Thus, we investigated the effects of consecutive intake of fermented soymilk (FSM) with LcS on skin condition and the gut microbiota, as well as isoflavone bioavailability, in a randomised, double-blind, placebo-controlled trial as a pilot study. Sixty healthy premenopausal Japanese women received FSM containing a moderate level of isoflavone aglycones and a probiotic LcS, or soymilk (SM) containing neither of them, twice a day for 8 weeks. Skin condition was assessed by a subjective questionnaire for face and morphological analysis of the stratum corneum on the inner forearm. Faecal microbiota and urinary isoflavone were analysed by 16S rRNA gene amplicon sequencing and high-performance liquid chromatography tandem mass spectrometry, respectively. Both the FSM and SM groups had improved skin condition as assessed from scores of overall satisfaction, dryness, moisture, elasticity, coarseness, pigmentation and/or stratum corneum morphology, as well as significantly increased levels of urinary isoflavones during the intake period compared with the pre-intake period, although there were no significant differences between the two groups. There was a significant positive correlation between urinary isoflavone levels and skin questionnaire scores. In contrast, the relative abundance levels of Lactobacillaceae significantly increased and those of Bifidobacteriaceae tended to increase during the intake period compared with the pre-intake period. For the after-intake period they only decreased significantly in the FSM group. The levels of Enterobacteriaceae and Porphyromonadaceae significantly decreased during the intake period in the FSM group. These findings suggest that daily intake of FSM, as well as SM, provides health benefits that improve skin condition via increased levels of isoflavone absorption in the body, and that only FSM beneficially modifies the gut microbiota in premenopausal healthy women.