Posted on Mon, 7 Jan 19
Fermented foods are of increasing interest nutritionally because they are a source of bacteria which may confer health benefits. But are they healthy or is it just hype? A new review summarises the science.
Kefir, kimchi… fermented foods are rapidly growing in popularity as health foods. An excellent update on the state-of-the-science in the journal Nutrition Reviews explores the evidence for fermented food-derived bacteria .
Most people are estimated to ingest between 1 to 10 billion bacteria daily, the majority of which come from fermented foods, point out the study authors. However, one of the controversies around fermented food-derived bacteria is whether or not they reach the gastrointestinal tract in sufficient amounts to influence the resident gastrointestinal microbiota and/ or our health.
Despite anti-microbial defences in saliva, stomach acid, pancreatic enzymes, bile, and strong resistance to colonization by foreign bacteria in the gastrointestinal tract, evidence does indeed suggest that, against all the odds, bacteria in fermented foods can not only survive transit through the gastrointestinal tract but can influence our microbiome and exert gastrointestinal and systemic health benefits.
Epidemiological studies have provided some evidence that fermented foods, in particular yoghurt, may be associated with health benefits including reduced risk of metabolic syndrome, certain cancers, cardiovascular disease, and type 2 diabetes.
Clinical studies have also suggested yoghurt may have some favourable effects on metabolic risk markers [reviewed in 2], but clinical trials have often found that ‘probiotic yogurts’ (those with probiotic bacteria added to the yoghurt) are generally more effective than ‘conventional yogurts’ with only the fermentation-associated microbes.
“Relatively few human clinical studies that examined the effect of fermented vegetables or other fermented foods on health outcomes have been described in the literature,” note the authors. Although there is some evidence suggesting beneficial effects of kimchi (Korean fermented vegetables) and kochujang (Korean fermented soybean-based red pepper paste).
“The hypothesis that diets rich in fermented foods containing live organisms could redress a dysbiotic intestinal microbiota is an attractive proposition, but it is not new,” concluded the reviewers. “More than 100 years ago, the Nobel laureate Ilya Metchnikoff wrote the following prescient passage: “The dependence of the intestinal microbes on the food makes it possible to adopt measures to modify the flora in our bodies and to replace the harmful microbes by useful microbes.”
“However, as Metchnikoff also noted, the absence of suitable methods was a major challenge. “Unfortunately, our actual knowledge of the intestinal flora is still very imperfect because of the impossibility of finding artificial media in which it could be grown. Notwithstanding this difficulty, however, a rational solution of the problem must be sought.”
With detailed analysis of the hidden microbial world now possible, we are sure to see an increase in research exploring the possible health benefits of probiotic microbes derived from fermented foods.
1. Kok CR, Hutkins R. Yogurt and other fermented foods as sources of health-promoting bacteria. Nutr Rev. 2018 Dec 1;76(Supplement_1):4-15
2. Dumas AA, Lapointe A, Dugrenier M, Provencher V, Lamarche B, Desroches S. A systematic review of the effect of yogurt consumption on chronic diseases risk markers in adults. Eur J Nutr. 2017 Jun;56(4):1375-1392.