The Keto Guide to Fermented Food, Part 3

Which fermented foods are great for keto and which should you avoid?

Article by Mandy Pagano | 20 Dec, 2020

Article originally published on on 2/7/17. It has been lightly edited for re-publication.

Editor's note: We here at Ketogenic Success want to make it clear that we are not telling people what to eat. The opinions expressed in this piece are strictly based on the available, objective evidence as of the time of this writing and are subject to change should more data become available. We try to provide you, Dear Reader, with enough information so as to make an informed decision about what foods you do or do not include in your ketogenic lifestyle.

In previous weeks we went over what fermented foods are and why they're all the rage in the health and nutrition community. We also explored the differences between fermented goods that are processed by food manufacturers and those that are made at home.

This week we're getting to what everyone really wants to know: Which ones can a ketonian eat?

From our research there seem to be two categories when it comes to fermented foods: (1) Known As Safe,  and what we call (2) The Grey Area (Unknown/Potentially Unsafe).

Known as Safe

There are certain fermented foods that we know for certain, via an extensive body of scientific evidence, actually do show boosts of probiotics in the gut post-consumption, are known as safe to consume in normal quantities, and are low carb enough that the average ketonian should feel perfectly comfortable and confident incorporating them into a ketogenic lifestyle.

This category encompasses fermented milk products (plain yogurt, kefir, crème fraîche, sour cream, curd, and cheeses), and fermented vegetables (the most common of which are cabbage-based like kimchi or sauerkraut, are cucumber or pepper-based, or are some kind of chutney). As discussed last week and reiterated here, there are conditions to consuming these foods for the probiotic benefits.

  1. They must be unpasteurized
    • Pasteurization kills off any beneficial bacteria. While eating cheeses or sour cream, for instance, may be tasty and perfectly keto friendly, if they have been pasteurized prior to packaging (and most have) then you're not getting the probiotic benefits of fermentation.
  2. Know where to look
    • You are unlikely to find ideal fermented foods in a can or jar in the shelf stable aisles at the local grocer's. Fermented foods that are unpasteurized and containing live, active cultures are most commonly stored in the refrigerated sections of the grocery store.
  3. Closely examine labels
    • Both milk/cream products and vegetables generally have enough natural carbohydrates in them to ferment without adding sugar to the brine. If sugar is in the ingredients list, you should consider skipping it simply because it will have a higher carbohydrate impact than it would otherwise.

The Grey Area

This is where we're going to disappoint a lot of people. Basically everything else, including some very beloved fermented products, falls into this category for a variety of reasons. This classification does not mean you should never consume these foods. What we urge is for every individual to examine the evidence for themselves, weigh it accordingly, then make an informed decision as to whether or not to incorporate these products into your ketogenic lifestyle.

Kombucha is a good example of a fermented good that is very popular right now as a potentially healthy drink. The problem- and why we classify this as grey area- is that one word: potentially.

Unfortunately the evidence for Kombucha isn't very encouraging as of the time of this writing. Despite the many health claims made by Kombucha proponents, during research we did not find any clinical trials that showed health benefits (gut or otherwise) associated with Kombucha consumption. And we are not alone. We found several systematic reviews, in which researchers looked for evidence of clinical trials showing the safety and efficacy of Kombucha, and they turned up nothing as well.

We also rather alarmingly discovered that this popular drink can very easily become toxic if it is not brewed under impeccably sanitary conditions. It is listed as possibly unsafe by WebMD, and the FDA actually recommends against drinking home brews because of the sanitation issue as well as the difficulty in maintaining the right temperatures and acidity levels required to inhibit dangerous bacterial growth. The CDC has warned against excessive Kombucha consumption of more than 4 fluid ounces a day and against it altogether in persons who may have underlying medical conditions making them more susceptible to infection or metabolic acidosis. There is also the possibility of severe allergic reaction to the "mushroom" that is integral to making the brew.

Other problems with Kombucha (the commercial kind) are more due to manufacturing for flavor. Juices and extra sugars are more often than not added to the base product to make it palatable. This means that the majority of the sugars in your bottle are not consumed during the ferment and it may be either higher in carbohydrates than a ketonian should reasonably consume, or undesirable altogether for ketonians with very severe insulin resistance issues.

A fairly substantial number of the remaining fermented foods that are popular and widely available are in the grey area because they are soy based. Familiar fermented soy products are stinky tofu (regular tofu is not fermented), natto, fermented bean paste, miso, soy sauce, tamari, and tempeh.

One of the main problems with soy products, in general, is that they are goitrogenic. This means they contain high amounts of goitrogens, which are chemicals known to interfere with hormone production in the thyroid. You can read about the controversial nature of soy (with lots of footnotes!) here. You may also peruse the plethora of studies linking soy and the goitrogenic isoflavanoids in them to a variety of health conditions (most of which are hormonal) here.

It has been asserted by some alternative medicinal sources that traditional soy fermentation may inhibit or eliminate the goitrogens, but unfortunately at the moment that is more speculation than science. As with Kombucha, there is no clinical evidence that there is any benefit to consuming fermented soy products, and there is also no evidence that fermentation negates the goitrogenic properties of soy. In fact, many experts believe fermentation may actually increase the goitrogenic effects of soy, by freeing the goitrogens from the sugars with which they are molecularly joined (remember fermentation eats sugar) thereby making them more readily absorbable by the body instead of less.

It has been asserted that Asian populations eat lots of soy (which is mostly fermented) and are, generally, healthier than Western populations. While we in the West tend to think of soy products as staples of Eastern diets, in fact it is more appropriately deemed a condiment. The average soy consumption in China, for example, is around 2 teaspoons per day, so the idea that Eastern populations are consuming massive amounts of soy and maintaining excellent health is misinformation, at best.

This is not to say that these grey area foods are completely out of the question. Simply put, there is not sufficient evidence to confidently declare them as safe for regular consumption for any lifestyle, much less a ketogenic one. At the same time, we acknowledge that just because there is not currently evidence that these foods are safe for a ketonian does not mean that such evidence will never exist.

Further, as adults we must all make our own choices when it comes to what we consume. While we may not be able to recommend using Kombucha or natto as good sources of probiotics, you are the ultimate judge and must make your own decisions. Hopefully, through this series we have provided enough information in one place for your decision to at least be an informed one.

As with all foods, if you do choose to consume fermented goods that fall within the grey area, be sure to follow rules one through three in the section on safe foods above. Reading labels and being aware of what's in your food and what state it's in is important no matter what you're consuming.

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