In the new Gut Microbiota for Health “Clinical Minute” series, we get a scientific expert’s take on one or more gut-microbiota-related questions that patients frequently ask their healthcare professionals.
TOPIC: Do fermented foods contribute to health?
Dr. Mary Ellen Sanders (MES) is the founding president of a non-profit association of academic and industrial scientists called the International Scientific Association for Probiotics and Prebiotics (ISAPP), and currently serves as ISAPP Director of Scientific Affairs/Executive Officer. She consults internationally in the area of probiotic microbiology.
MES: Consumer interest in fermented foods is high—these foods are discussed frequently in media related to food and health, and the US supermarket chain Whole Foods Market recently included fermented foods in its list of the top food trends of 2016. But what do we really know about fermented foods and health?
Patient question: What are fermented foods?
MES: As defined in a recent review article that was an outcome of the 2016 ISAPP meeting, fermented foods are “foods or beverages made through controlled microbial growth and enzymatic conversions of major and minor food components” (Marco et al. 2017). These include thousands of foods consumed by populations around the world, from chocolate and coffee to traditional sauerkraut and kimchi. Some fermented foods contain live microbes when consumed, and others do not. (Some processing steps kill or remove the live microbes.) A descriptive infographic on fermented foods is available from ISAPP.
Patient question: How do fermented foods differ from probiotics?
MES: It’s important to distinguish between fermented foods and probiotic foods. A subset of fermented foods that contain live microbes qualify as “probiotic”, but only if the microorganisms are characterized (known) and if research has associated them with a health benefit. The foods in this category include many commercial yogurts and some kefir products that list the bacterial species they contain.
Patient question: What health benefits are associated with fermented foods?
MES: A limited number of controlled human trials have been carried out on fermented foods (summarized in Table 2 of Marco et al. 2017), but direct evidence for health benefits of fermented foods is limited. Clearly, fermented foods provide the nutritional benefits associated with the nutrients contained in the foods. But for the fermented foods that are not also probiotic foods, we know little about extra benefits associated with the presence or growth of the fermenting microbes.
In cohort studies, consumption of fermented dairy foods is associated with weight maintenance (Mozaffarian et al. 2011), as well as a reduced risk of cardiovascular disease (Tapsell 2015) and type 2 diabetes (Chen et al. 2014). A few randomized, controlled trials have been conducted on different endpoints of metabolic syndrome, providing some causal proof of observations in associative studies. Furthermore, particular fermentation microorganisms in food are associated with certain health benefits. For example, yogurt cultures are known to improve tolerance of lactose by lactose intolerant people.
A vast number and variety of fermented foods exist, and surely they do not all lead to similar health benefits. Researchers have proposed, for example, that, depending on the raw materials and the microbe(s) responsible for the fermentation, ingestion of a fermented food could in theory inhibit the growth of pathogens in the gut, enhance nutritional value through increased vitamin synthesis or absorption, and/or improve food digestibility, among other things.
Patient question: By what mechanisms might fermented foods impact health?
MES: Scientists have some insights into how fermentation microbes may impact health. Some produce short chain fatty acids in situ, which are associated with many different health outcomes, including direct inhibition of intestinal pathogens. Some produce B vitamins during growth in the food, increasing the food’s nutrient profile. During the fermentation process, some secrete proteins and exopolysaccharides that act as anti-oxidants, prevent adhesion of intestinal pathogens, enhance immune responses, or improve blood lipids. But research gaps remain and these benefits need to be confirmed.
The number of live microbes contained in different fermented foods at the time of consumption is often unclear, but this question is being investigated for an upcoming review article commissioned by ISAPP.
Patient question: Do the live microbes in fermented foods support my gut microbiota?
MES: Researchers working on the gut microbiota have long observed that (1) the colonizing microbiota is important to health, and (2) modern diets, compared to diets of early man, are significantly lacking in live microbes. Dietary live microbes provide ongoing exposure of our alimentary canal to a fresh source of microbes. Many of these may not survive through the digestive process – our stomach and upper small intestine are harsh environments. But the ones that do survive, and components of the ones that don’t, have the potential to interact with the host, impacting immune, neurological, and other host systems.
SUMMARY: Fermented foods are associated with positive health effects.
MES: Overall, it appears that many fermented foods are associated with positive health effects, but we lack controlled clinical research to confirm this relationship. The subset of fermented foods that qualify as probiotic may have unique benefits attributable to the live microorganisms. Consuming fermented foods will at least temporarily bolster the live microbes transiting through the gut, and that is likely a good thing. Patients who want to find ways of adding fermented foods to their diet should be advised to seek the advice of a registered dietitian.
Chen, M. et al., 2014. Dairy consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis. BMC Medicine, 12(1), p.215. Available at: http://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-014-0215-1
Marco, M.L. et al., 2017. Health benefits of fermented foods: microbiota and beyond. Current Opinion in Biotechnology, 44, pp.94–102. Available at: http://linkinghub.elsevier.com/retrieve/pii/S095816691630266X
Mozaffarian, D. et al., 2011. Changes in Diet and Lifestyle and Long-Term Weight Gain in Women and Men. New England Journal of Medicine, 364(25), pp.2392–2404. Available at: http://www.nejm.org/doi/10.1056/NEJMoa1014296
Tapsell, L.C., 2015. Fermented dairy food and CVD risk. British Journal of Nutrition, 113(S2), pp.S131–S135. Available at: http://www.journals.cambridge.org/abstract_S0007114514002359