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Common Confusion – Fermentable foods vs fermented food

Updated: Oct 14, 2019

I have been told by dozens of patients that they were avoiding all fermented foods based on our diet handouts for SIBO treatment and prevention. Was that really in our recommendations? I sure didn’t believe it was correct. It is true, some highly sensitive people react to fermented food. Perhaps this is due to histamine sensitivity, because the fermentation and aging process may produce histamine. Others might react to acids (acetic, butyric, etc.) or traces of yeast, ethanol or some other fermentation metabolite, but barring an individual response, there seems no reason to remove these foods from the diet of patients with bacterial and yeast overgrowth. I now think that many of us, including some healthcare professionals, conflate foods that have high fermentation potential with fermented foods.

Highly fermentable foods

Researchers and clinicians such as S. Haas, E. Gottschall, N. Campbell-McBride, SJ Shepard and PR Gibson, M. Pimentel, A. Siebecker, N. Jacobi and N. Robillard, have developed the modern dietary concepts underlying low fermentation diets. These diets organize common foods into various degrees of fermentation potential, allowing patients to reduce in vivo fermentation. Some of our patients can partially or completely control their IBS or IBD symptoms by using one of these low fermentation diets. It is unlikely that these approaches cure bacterial overgrowth (although this has not been studied), but can effectively control the fermentation of carbohydrates and the symptoms caused by the byproducts of this process – painful distention of the GI lining, stool frequency and consistency changes, abdominal bloating, reflux, nausea, etc. The more highly fermentable carbohydrates are fructans, oligosaccharides, disaccharides, monosaccharides (opinions vary) and most sugar alcohols (1). These fall into the general categories of prebiotics/fiber. Bacteria, archaea and yeast ferment these carbohydrates into hydrogen, methane, hydrogen sulfide, and carbon dioxide gas (2). In addition, acids such as acetic, lactic and butyric as well as ethanol are common metabolites of these processes.

Fermented foods

The same biochemistry applies to fermented foods. The big and essential difference is that this is an in-vitro process. Although the same gases and metabolites are produced, the gases escape into the environment. Fermentation locks, airlocks or water-sealed crocks are used to keep contaminants and oxygen out of the mix and allow the gases to escape during the process of fermentation in vitro. Unless the patient is sensitive to some other metabolite, the usual problems induced by gas pressure and chemistry are not an issue with fermented food. All the health benefits of fermentation – organic acids, anti-microbial agents, bioactive peptides, probiotics and nutrients (3) – can be ingested without the in vivo issues of gas accumulation.

Types of Fermented Foods

The common list includes beer, wine, yogurt, kefir, cheese, sourdough, fermented meat (salami, etc.), pickles, olives, sauerkraut, kimchi, fish sauce, tempeh, miso, soy sauce and kombucha (fermented tea). Cocoa and various ethnic foods may also be fermented.

Health Benefits of Fermented foods

Although it is believed that the probiotic organisms in fermented foods are “just passing through” and not creating an ecological niche in the gut flora, there is plenty of evidence of their benefits (3). It is thought that they do not persist in the gut for more than a few days. Frequent consumption of fermented foods leads to a “transient microbiome”. They are thought to influence the diversity and function of the gut microflora (4). Common organisms include various species of Lactobacillus. Leuconostoc, Streptococcus and Bifidobacteria. Even if the bacteria are not viable, there is significant benefit. These probiotics and their benefits include

· Fermented dairy and metabolic syndrome (5)

· Fermented soy and Type 2 diabetes mellitus (6) and hypertension (7)

· Probiotics and body weight and blood lipids in obese individuals (8)

· Yogurt and bladder cancer incidence (9)

· Yogurt and body weight (10)

· Probiotics and infantile atopic dermatitis (11)

· Probiotics and asthma prevention in the prenatal and neonatal periods (12)

· Yogurt and lactose intolerance (due to in vivo beta-galactosidase production) (13)

· Probiotics and superoxide dismutase upregulation in colitis (14)

· Probiotics and prevention of antibiotic associated diarrhea in children (15)

Additional benefits are improved mineral absorption by bacterial degradation of phytates via phytase production in breads (16), and increased polyphenols production in beer (17) and antimicrobial compounds in fermented milk (18).

Some so-called fermented products are “fake” in that they are not truly fermented. Instead they are processed with lye, salt or vinegar. This includes some pickles, olives and sauerkraut and these are not expected to have the same health-promoting effects as true fermented foods.

I am not a microbiologist and certainly do not consider myself an expert on probiotics. I wrote this column to take a closer look at this common misconception of fermentation potential of foods versus fermented foods. I welcome your comments on the information included in this article. Direct any comments to


1. Low-FODMAP Diet Improves Irritable Bowel Syndrome Symptoms: A Meta-Analysis. E, Altobelli. 9, Aug 26, 2017, Nutrients. , Vol. 9, p. pii. E940.

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10. Changes in diet and lifestyle and long-term weight gain in women and men. Mozaffarian. 25, Jun 23, 2011, N Engl J Med., Vol. 64, pp. 2392-404.

11. Treatment efficacy of probiotics on atopic dermatitis, zooming in on infants: a systematic review and meta-analysis. M, Zhao. 6, Jun 2018, Int J Dermatol. , Vol. 57, pp. 635-641.

12. Efficacy of probiotic supplementary therapy for asthma, allergic rhinitis, and wheeze: a meta-analysis of randomized controlled trials. X, Du. 4, Jul 1, 2019, Allergy Asthma Proc. , Vol. 40, pp. 250-260.

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14. Host lysozyme-mediated lysis of Lactococcus lactis facilitates delivery of colitis-attenuating superoxide dismutase to inflamed colons. SA, Ballal. 25, Jun 23, 2015, Proc Natl Acad Sci U S A. , Vol. 112, pp. 7803-8.

15. Probiotics and antibiotic-associated diarrhea in children: A review and new evidence on Lactobacillus rhamnosus GG during and after antibiotic treatment.

16. Phytase activity of lactic acid bacteria and their impact on the solubility of minerals from wholemeal wheat bread. D, Cizeikiene. 7, 2015, Int J Food Sci Nutr. , Vol. 66, pp. 736-42.

17. Use of Saccharomyces cerevisiae var. boulardii in co-fermentations with S. cerevisiae for the production of craft beers with potential healthy value-added. A, Capese. Nov 2, 2018, Int J Food Microbiol. 2018 Nov 2;284:22-30., Vol. 284, pp. 22-30.

18. Brazilian Kefir-Fermented Sheep's Milk, a Source of Antimicrobial and Antioxidant Peptides. MDSF, de Lima. 3, Sept 2018, Probiotics Antimicrob Proteins. 2018 Sep;10(3):446-455, Vol. 10, pp. 446-455.

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