Fermentation has been described as ‘a better invention than fire’. Hmmm, I wonder if this just relates to fermented drinks (wines and beers)? Would the same accolade be awarded to fermented foods without the drinks?

Fermented foods are beloved of preppers who store away non-perishable nutrient dense foods, just in case.

Fermented foods are also popular among the clean foodies for the proposed health benefits. Proposed benefits of fermented foods include reduced fatigue, improved digestion and elimination, lower cholesterol and blood pressure, cancer prevention and prevention of radiation injuries.

I doubt that the scientific literature has proven (unequivocally) that fermented foods are a better invention than fire, but maybe fermented foods have some proven health benefits?

What Are Fermented Foods?

Fermentation is a process by which microorganisms convert food into other products via the production of lactic acid, ethanol, and other metabolic byproducts.

Put another way, fermentation involves the slow decomposition of organic substances by microorganisms, or by enzymes of plants or animal origin. Biochemically speaking,  fermentation involves anaerobic or partially anaerobic oxidation of carbohydrates.

Fermentation is used to lengthen shelf life,  prevent spoilage and produce alcohol. While fermentation involves the anaerobic conversion of sugars to alcohol, it also produces energy for the microorganism or cell. Humans have been eating fermented foods for over 9000 years and it was a useful way to preserve food without refrigeration back in the day.

The history of fermented foods is interesting.

Captain Cook brought fermented foods (sauerkraut) on his voyages as he recognised that it is a rich source of vitamin C. Scurvy begone. The French chemist Louis Pasteur founded the science of zymology in 1856 when he connected yeast to fermentation. Research related to fermentation was even awarded the Nobel Prize (which is more than fire can claim).

When the atomic bomb dropped on Nagasaki in August 9 1945, physicians and patients who were just 1.4 kilometers away from the epicenter remained unaffected. The lead doctor at the unit contributed their survival to daily consumption of wakame miso soup, which is miso soup with seaweed. Based on this report Europeans prophylactically consumed miso soup during the Chernobyl disaster of 1986.

Later research supported the hypothesis that fermented foods help mitigate radiation damage. Pre-treatment with miso soup in mice was shown to protect mice from high dose radiation and showed increased crypt survival, crypt length, and prolongation of the time interval between the radiation and cell death (1).

I guess, the protective effects of fermented foods on radiation is another good reason for preppers to have fermented foods in their bug-out bags

Fermented foods include:

  • yogurt,
  • kimchi,
  • kombucha,
  • kefir,
  • tempeh,
  • natural pickles,
  • sauerkraut,
  • miso and natto.

Some fermented foods (yoghurt) require a ‘starter’. The starter contains bacteria. In the case of yoghurt, the starter is added to milk. The bacteria digests the sugar in the milk and creates yoghurt. On the other hand, sauerkraut does not need a starter, as the natural cabbage juice contains the bacteria needed to turn cabbage into sauerkraut.

‘Pasteurized fermentation’ products is essentially an anathema. Fermentation requires bacteria.


Miso is a fermented soybean paste, which is a traditional ingredient in Japanese cuisine. It is used as a flavoring in soup and traditional Japanese dishes (1). Miso has been adopted into Western cultures as a stock for soups and salads. It can be a mixture of soybeans, rice, wheat, minerals, vitamins, microorganisms, salt, plant proteins, carbohydrates and fat. Miso has a very high salt content, but salt reduction during fermentation can lead to spoilage of food and food poisoning.


Natto is fermented soybean, also known as shu douchi. It is a fermented soy product with a high content of menaquinone-7 or Vitamin K-2, which is an isoflavones that can help prevent post-menopausal osteoporosis. The natural content of vitamin K-2 in natto is more than 100 times that of cheeses and is believed to catalyze gamma-carboxylation (2).


Kimchi is a traditional Korean food manufactured by fermenting cruciferous vegetables with probiotic lactic acid bacteria along with garlic, ginger, and red pepper powder. Kimchi is considered to be a vegetable probiotic (3). Kimchi is rich in probiotic lactic acid bacteria. Key bacteria present in kimchi include leuconostoc, lactobacillus, weissella, bifidobacterium and saccharomyces (4).


Tempeh is a fermented soy product with a higher ratio of isoflavones than tofu.


Pickles (e.g. cucumbers) are pickled in a brine, vinegar, or other solution and left to ferment for a period of time. Many pickles today are pasteurized and lack beneficial bacterial cultures. Live pickles have to be kept in the refrigeration section of any store (which is a good way to identify live pickles or fermented foods).

The theoretical health benefits of fermented foods are threefold:

1. During fermentation, live bacteria break down food making it easier to digest the food and absorb the nutrients. Fermentation does some of the digestive work and makes food more digestible. This makes it easier for humans to absorb the nutrients contained within the food.

2. Fermentation can also boost the nutritional content of food. For example, fermentation can produce B vitamins in food that the food does not naturally contain.

3. Fermentation can enrich the gut bacteria and can have favourable effects on the human microbiome (see later section).

There are 2000 products for sale on Amazon relating to fermented foods, which includes books, capsules and glass fermentation jars and expensive picklers.

Fermentation is very popular.

Fermented foods made Whole Foods top five food predictions for 2016.

The #hashtag fermentation has almost 400,00 posts on Instagram.

Is There Any Research?

There are 8,581 publications related to fermented foods including 200 clinical trials. To put this into context, there are over 20,000 publications relating to probiotics which include over 2,000 clinical trials.

Do Fermented Foods Help Osteoporosis?

A study in the Japanese population based osteoporosis study cohort evaluated the effect of habitual natto intake and bone mineral density in 944 women (5). There were statistically significant positive associations between natto intake and a protective effect on bone mineral density at the neck of the femur and the radius in post-menopausal women.
No association was found between intake of tofu or other soybean products and bone mineral densities. The authors concluded that the menaquinone-7, which is more abundant in natto as opposed to soybean products is the most likely bio-active bone protective component and may be particularly helpful in women who have low-affinity receptors for Vitamin D.

Bottom Line

There is some evidence to support a role for natto and bone health. However this cannot be extrapolated to other fermented foods as natto has unique constituents which are believed to affect bone health.

Do Fermented foods Affect BP?

Danish investigators conducted a full Cochrane Review in 2012, looking at the effects of fermented milk and hypertension (6). The review does not support any positive effect of fermented milk on blood pressure, and the authors recommended against the use of fermented milk to influence blood pressure at a population level.

Bottom Line

Fermented milk does not help lower BP.

Does Eating Fermented Foods Give You Probiotics? (And does that matter?)

The human microbiome has captured the poll position in medical research over the last number of years. We learned absolutely nothing about the microbiome in medical school. How things have changed.

Here are the key terms that are used in this emerging field of research.


The microbiome refers to the microbes (bacteria, viruses, fungi) that live within us and on our skin. The microbiome outnumbers human cells in a ratio of 10 to 1, and account for about two pounds of our total body weight. (No, you can’t lose weight by eliminating your micrbiome. You simply cannot survive without it).

The genetic load of the microbiome outweighs human genetic material 100 to 1. In many ways, we are just scaffolding for our microbiome.

Quite a humbling thought really.


The human gut is sterile at birth and evolves to contain 10,000,000,000,000 bacterial cells per gram of luminal content.

Bacteria present in the intestinal tract extend a profound effect on our health and are called the human microbiota.


Dysbiosis is a term given to a situation where there is a disturbance in the normal healthy microbiota balance or microbiome.


Prebiotics are selectively fermented ingredients that can change the composition of the human microbiome.


Probiotics are microorganisms that can confer a health benefit to the human host.

Lactic Acid Bacteria

Lactic acid bacteria are non-pathogenic, non-toxigenic gram positive fermenting bacteria that produce lactic acid from carbohydrates in the process known as fermentation.

From a basic science perspective, fermented foods are a source of probiotics. By definition, probiotics confer health benefits.

The aim of fermented foods is not to specifically increase a relative percentage of any single bacteria within the microbiome, but to increase the overall diversity of the microbiome.

Fermented foods are an excellent way to add diversity to the microbiome. Even though most of the bacteria in fermented foods do not actually take up permanent residence in the gut, they do produce beneficial effects as they pass through.

Bottom Line

Fermented foods are a source of probiotics which confer health benefits to the human host.

Is Eating Fermented Foods Good For Diabetics?

The effect of fermented red ginseng on glycemic control was evaluated in a placebo controlled trial in 45 Korean adults (7)

Fermented red ginseng led to a significant reduction in post prandial glucose in subjects with impaired glucose control as compared to placebo

Eleven healthy subjects consumed a control and test meal in a randomized cross-over design (8). The test meal, comprising 200 g of boiled white rice with a ‘viscous meal’ (50 g natto, 60 g Japanese yams and 40 g okras), and the control meal, comprising 200 g of white rice with non-viscous boiled soybeans, potatoes and broccoli. The test meal was associated with a significantly lower post prandial blood glucose level.

Korean investigators enrolled 21 adults with pre-diabetes in a study (9). Study participants received either fresh (1 day old kimchi) or fermented (10 day old kimchi) for 10 days. After a four week washout period, they switched to the alternate form of kimchi. Consumption of both types of kimchi significantly decreased body weight, body mass index, and waist circumference. The percentages of participants who showed improved glucose tolerance were 9.5 and 33.3% in the fresh and fermented kimchi groups, respectively. Fermented kimchi had additional effects on BP and insulin resistance/sensitivity.

Malaysian investigators found that fermentation using Mardi Rhizopus sp. strain 5351 inoculums could enhance the antihyperglycemic and the antioxidant effects of mung bean in alloxan-treated mice (10).

A total of 41 Korean patients enrolled in an intervention trial to evaluate the Korean traditional diet in patients with hypertension and/or diabetes and hypertension (11). The control group was advised to “eat as usual,” whereas the experimental Korean Traditional Diet diet group was fed the Korean Traditional Diet  three times a day for 12 weeks. Regular consumption of the Korean Traditional Diet for 12 weeks by hypertensive and Type 2 Diabetes patients resulted in favorable changes in cardiovascular risk factors.

This raises the question as to whether the health benefits are due to the fermentation process or the parent compound or maybe both e.g. soy versus natto.

Dutch investigators evaluated the effect of replacing meat protein with soy protein on insulin resistance in 15 post menopausal obese women (12). This study has been included here as a lens on soy in diabetes .

A randomized crossover trial of a diet contained protein of mixed origin (mainly meat, dairy, and bread) versus a diet partly replaced meat with soy meat analogues and soy nuts containing 30 g/d soy protein over 2- 4 weeks.  The soy-protein diet resulted in statistically greater insulin sensitivity and lower cholesterol compared to the meat based diet.

Bottom Line

Fermented foods may offer health benefits in diabetes. However, it has to be said that fermented foods are not a single entity but a diverse group of foods. It would be far better to study and recommend the use of a specific fermented food as opposed to using the umbrella term ‘fermented foods’ as different foods may offer differential effects.

Does It “Prevent The Growth of Pathogenic Bacteria”?

 There are two main clinical presentations of overgrowth of pathogenic bacteria: antibiotic associated diarrhea (Clostridium difficult infection) and intestinal bacterial overgrowth syndrome.

A double-blinded randomized placebo-controlled was conducted in Washington DC and looked at the effect of kefir on antibiotic associated diarrhea (13).

A total of 125 children aged 1 to 5 years presenting to primary care physician were given kefir to see if it can prevent antibiotic associated diarrhoea. The study has a negative results and showed that kefir did not prevent antibiotic associated diarrhea.

Symptoms of irritable bowel and small intestinal bacterial overgrowth syndrome are associated with an altered gut microbiome. There is nothing specific looking at fermented foods for irritable bowel .

There is a Cochrane review which evaluated the effects of probiotics in the treatment of irritable bowel syndrome (14). I think that this is worth including here even though it does not directly relate to fermented foods per se. A total of 19 randomized controls and 1650 patients were selected for the overview. Probiotics were statistically significantly better than placebo, but there was significant heterogeneity in study results. The authors concluded that probiotics were helpful in inflammatory bowel disease, but that the magnitude of the effect was unclear.

Bottom Line

There is no direct proof that fermented foods prevent the overgrowth of pathogenic bacteria.

Do They Help The Body Produce Acetylcholine? (And does that matter?)

I have not thought about acetylcholine in years (not since 3rd med pharmacology). Acetylcholine is a neurotransmitter that acts at neuromuscular junctions, the central nervous system and some body organs.

Chinese investigators studied the acetylcholinesterase  inhibitory activities of commercial sufu and self-produced sufu (15). Sufu is a form of fermented Chinese soybean.

High levels of acetylcholinesterase inhibition would increase the amount of acetylcholine available by preventing the breakdown of the compound. Fermentation of soybean extracts with A. elegans resulted in  higher anti-AChE activity than did the potato extracts.

Interesting, but very far removed from clinical practice and it is very hard to draw any conclusions about what this might/might not mean.

The mandarin Hon-Chi is the red yeast rice fermented with Monascus pilous and Monascus purpureus.

Hon-Chi was given to fasting Wistar rats (16). The study design was complex and involved measuring blood glucose and assessing acetylcholine function at nerve terminals.

The study found that Hon-Chi increased release of acetylcholine from nerve terminals. The acetylcholine then  stimulated muscarinic  receptors in pancreatic cells and and released insulin and lowered glucose.

Bottom Line

There is nothing in the scientific literature to support any clinically relevant role for fermented food and acetylcholine.

Does It Improve Digestion?

Japanese subjects who consume more than three bowls of miso soup per day have a 60% higher rate of gastric carcinoma than those who do not (17). The Japanese Collaborative Cohort (JACC) Study for Evaluation of Cancer Risk was a study of 15732 men and 24997 women between 40 and 79 years of age. The study showed that gastric cancer was 60% higher in people who consumed more than or equal to three bowls of miso soup per day. Sodium intake had a linear correlation with a risk of gastric carcinoma (P=0.002). The authors of the study concluded that the high salt intake of miso soup was a causative factor in the excess gastric cancer seen in this cohort.

A study in 20 consecutive patients with constipation were given 500 mL/day of a probiotic kefir beverage was administered to all patients for 4 weeks (18).

Study participants reported an increased stool frequency (p<0.001), improved stool consistency (p=0.014), and decreased laxative consumption (p=0.031). The degree of straining during evacuation showed a tendency to improve after kefir administration but did not reach the level of statistical significance. Fermented foods may not benefit people who already have normal healthy gut and a healthy gut flora.

Bottom Line

Fermented foods do not seem to help with digestive issues.

Is Eating Fermented Foods Safe?

Side effects of fermented foods include gas, bloating, or change in bowel habit. Fermented foods are also very rich in sugar content, and so care has to be taken in diabetic patients. Fermented foods can also have a very bitter taste.

Fermented foods are associated with an increased risk of gastric and oesophageal carcinoma (17, 19). Specific fermented foods can have individual signature toxicity risks.

Kombucha has been associated with suspected liver damage, metabolic acidosis, cutaneous anthrax infections and even deaths (20).

Natto can increase the levels of vitamin K in plasma and negate the effects of blood thinning medication such as warfarin or coumadin. A study found that boiling significantly reduced the Bacillus subtilis count and also  reduced the content of menaquinone-7 (MK-7). (21)

The authors suggested that boiling natto could make it safe for people on blood thinning. However, I would strongly recommend checking in with your own doctor and closely monitoring your blood coagulation if planning to take any kind of natto with blood thinners.


Theoretically, fermented foods could offer numerous health benefits. But there is a big problem. The key problem is not just that there is very limited research. (I have to admit that the key problem was not immediately obvious to me). However, as I dived into the research for this article, it became apparent.

The problem is that not all fermented foods are created equally. Any blogs or infographics that set out to answer the question of the health benefits of ‘fermented foods’ are fatally flawed.

Fermented foods are not a thing. Fermented foods are certainly not a single entity. They vary hugely in terms of the parent compound, the bacteria used and the actual fermentation process. How can we lump sauerkraut, kefir and pickles in the same research category? It is no wonder that the results of the research are so inconclusive.

We need to do targeted studies looking at the effects of specific fermented foods for select medical conditions. We also need to compare and contrast the health effects of different types of fermented foods for select medical conditions.

With great respect, I have to say that fermented foods come nowhere close to fire. Fermented drinks, well that is another story.

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