This important symposium brought together many nutrition professionals. It was an opportunity for YINI to invite leading experts to talk about the most recent perspective on the benefits of live microbes in fermented foods and gut microbiome. They highlighted what happens in both the pot and the intestine to better understand the health effects of yogurt.
Is the gut microbiota the intersection between diet and health?
The gut microbiota is gradually revealing its secrets. We now know that its ecosystem contains about 1000 different species of microorganisms, which encode more genes than the human host. Sharon Donovan (University of Illinois, USA) explained that these numerous genes interact with the human host through specific receptors located in the gut’s epithelial, neural and immune cells, as well as through the production of hormones and metabolites.
Recent research in animals has shown the essential role of gut microbiota in normal gastrointestinal, immune, metabolic and cognitive development and function. Human studies have highlighted that gastrointestinal conditions, such as inflammatory bowel disease and irritable bowel syndrome, but also other diseases such as obesity, type 2 diabetes and atopy, are linked to an imbalance of the normal gut microbiota (dysbiosis). It is therefore of great interest to better understand the role of dysbiosis in non-communicable diseases and to develop strategies to improve gut microbiota and health outcomes through diet. Review of the literature effectively suggests that diet can modify the intestinal microbiome, which in turn has a profound impact on overall health. This impact can be either beneficial or detrimental, depending on the relative identity and abundance of constituent bacterial populations. For example, it has been shown that a high-fat diet adversely reduces A. muciniphila and Lactobacillus, which are both associated with healthy metabolic states.
On the other hand, Sharon Donovan showed how dietary intake of prebiotics impacts positively the gut microbiome, and how fermented food containing live microbial species, such as yogurt or fermented dairy products enriched with probiotics, could benefit gut microbiome and health. Several groups have reported increased total bacterial load after regular consumption of fermented milk or yogurt. Notable increases in beneficial gut Bifidobacteria and/or Lactobacilli have also consistently been observed with several different types of probiotics. Probiotic-containing yogurt has been shown to significantly reduce counts of the enteropathogens E. coli and Helicobacter pylori.
A diet that is low in sources of prebiotics (soybeans, unrefined wheat and barley, raw oats, fructooligosaccharides (FOS)…) has been shown to reduce total bacterial abundance. On the opposite hand, high intake of these carbohydrates resulted in an increase in microbiota genes richness.
Donovan concludes with the observation that diet can modulate host-microbes interactions, which heralds a promising future therapeutic approach.
What happens in the gut?
Yogurt consumption has been associated with reduced risks of type 2 diabetes, metabolic syndrome, and heart disease, as well as improved weight management. By providing several key nutrients, yogurt is characterized by its live microorganisms (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. Bulgaricus), as well as strains of Bifidobacterium and Lactobacillus added specifically for their probiotic properties. Both culture organisms may benefit from the gut environment and, consequently, have an impact on health. These “probiotic” properties are of great interest for research. Robert Hutkins (University of Nebraska, USA) explored the interactions between ingested microorganisms and the gut microbiota, and the way exogenous microorganisms can change the gut environment.
The physiological mechanisms by which these microbes interact with the gut microbiota is the well-known phenomenon of colonization resistance. Recent research report that regular consumption of yogurt appeared to increase the numbers of Lactobacilli. The microbial diversity also appears to slightly increase with yogurt consumption in some subjects. The dairy matrix also matters! Still, dairy foods have long been the main delivery vehicle, and most probiotics do just fine in this matrix.
Clinical studies provide more and more evidence on the health benefits associated with yogurt consumption. Many recent studies have underlined the association between a greater microbial diversity and better health conditions, so this could be an important finding. For instance, it is well demonstrated that yogurt bacteria, via the enzyme β-galactosidase they provide, improve lactose digestion, allowing people with lactose maldigestion to eat yogurt. Research also shows that yogurt containing probiotics improves intestinal and extra-intestinal health, and leads to improved immune and anti-inflammatory responses to infectious diarrhea and respiratory infections. Hutkins also presented the latest areas of research on the microbiota-gut-brain axis, suggesting that probiotics and prebiotics could influence behavior.
In his conclusion, Hutkins also reminds that it is important to address the common misconception that fermented foods are the same thing as “probiotics”—the latter being live bacteria that confer health benefits when consumed in adequate numbers. Not all fermented foods contain live organisms. Beer and wine, for example, undergo steps that remove the organisms. Other fermented foods are heat-treated and the organisms are inactivated. Bread is baked and sauerkraut is often canned. So while these foods may be nutritious, they do not have probiotic activity, but may impact gut microbiota as well, as fermented foods.
What happens in the pot?
What could explain the health benefits of yogurt, reported by numerous epidemiological studies? Yogurt is a nutrient-dense food that contributes to the intake of protein, calcium, bioactive compounds and several micronutrients, which could help to explain some of its health benefits. Andre Marette (Laval University, Canada) presented recent evidence suggesting that dietary proteins can act as key regulators of immunometabolic factors and gut microbiota. Furthermore, he addressed several possible aspects that could explain the role of fermentation in the health benefits of yogurt. During the fermentation process of milk with yogurt cultures, dairy proteins are cleaved, generating in smaller molecules that can have some biological effects. These so-called bioactive peptides could explain the greater beneficial effect of yogurt on metabolic health compared with non-fermented dairy products, such as milk. Marette outlined potential mechanisms related to bacterial constituents and bioactive peptides produced during fermentation, that could be responsible for yogurt’s ability to protect against cardio-metabolic diseases (CMD). For example, the fermentation of yogurt may lead to an increased production of bioactive peptides with physiologic effects such as increased insulin sensitivity and glucose tolerance. Several peptides or peptide fractions have also been investigated for their bioactive properties such as anti-hypertensive, anti-thrombotic, satiety, opioid, immuno-modulatory, osteogenic, and antioxidant activities. Fermented dairy peptides and especially yogurt-type peptides generally exerted greater anti-inflammatory effects than other dairy products. These immunometabolic effects are associated with major taxonomic changes in the gut microbiota. Whether specific bacterial species are modulated by peptides released from fermentation from dairy products remains to be determined. These newly proposed mechanisms require therefore more research before being validated as a key factor in the protection against CMD, like type 2 diabetes or obesity.
A need for new dietary guidelines for fermented foods
Fermented foods and beverages have long been a part of the human diet, and with further supplementation of probiotic microbes, in some cases, they offer nutritional and health attributes worthy of recommendation of regular consumption. Despite the impact of fermented foods and beverages on gastro-intestinal wellbeing and diseases, their many health benefits or recommended consumption has not been widely translated to global inclusion in world food guidelines. Until now, dietary guidelines mainly focused on the nutrient needs, and consequently on the nutritional content of food. But for Seppo Salminen (University of Turku, Finland), it’s time to go further! Indeed, the health benefits associated with the consumption of fermented food, such as yogurt, are more and more evident, and the importance of beneficial microbes such as Lactobacillus in health promotion, by strengthening intestinal mucosal barrier, have been recognised. However, in Europe, only one health claim – on lactose digestion – has been approved for beneficial microbes. National nutrition guidelines or recommendations that include either probiotics or yogurt with live bacteria exist in five EU member states. Given that several physiological effects of probiotics are well established and that yogurt and yogurt with probiotics have benefits to humans, it has been suggested that yogurt should be part of food dietary guidelines. For Salminen, knowledge on health benefits is a real opportunity for evidence-based dietary guidelines with yogurt and yogurt with probiotic bacteria.
* IUNS 21st ICN, Buenos Aires, October 15-20, 2017.