A few months back, I was contacted by a British TV production company called Ricochet. They were in the process of planning the third season of a show called Superfoods: The Real Story and were looking for a scientific project about sauerkraut – one of the foods they focus on in season 3 – that they could feature on the programme. They had come across the protocol for the clinical trial I’m conducting on sauerkraut and irritable bowel syndrome and wanted to know whether I would be willing to appear on camera and discuss our project. I was happy for the opportunity to talk about my work/research on camera and said I would gladly appear on the show.
Yesterday, we shot the segment on sauerkraut at a medical facility in my hometown. It was a lot of fun. The presenter on the show, Kate, asked me a lot of questions about fermented vegetables, the human microbiome, nutrition, and so forth. Many of the questions she asked me revolve around topics that I think a lot of people – in particular the type of people that follow blogs such as this one – are interested in.
Unfortunately, most of my answers are probably going to be lost in the editing process; hence, they will never make it to the screen. For that reason, I thought I’d answer some of the questions here on the blog, so that you – the readers of Darwinian-Medicine.com – get to hear my thoughts on the things we talked about. I thought I’d focus on the microbes that are present in sauerkraut, as I think it’s an interesting theme.
The following questions form the basis of today’s edition of Ask Eirik:
How many bacteria are there in sauerkraut?
Sub-questions: What types of bacteria are there? Do all of these organisms survive past the stomach acid, and do they all colonize the gut?
– Question 1: How many bacteria are there in sauerkraut?
Fermented foods are packed with bacteria! A recent review paper entitled Health benefits of fermented foods: microbiota and beyond had the following to say about the concentrations of microorganisms in fermented foods such as kimchi and sauerkraut:
… some of the most familiar fermented foods, including sauerkraut, kimchi, kefir, dry fermented sausage, yogurt, cheese, kombucha, and miso ordinarily contain viable cells in notable quantities ranging between 106 and 109 cells/g or cells/ml. A relatively large fraction of those microbes survives passage through the human digestive tract. The ingestion of fermented foods potentially increases the numbers of microbes in the diet by up to 10 000-fold … (1)
Read the last sentence on more time and then take a second to let what it says sink in… As you can see, the consumption of fermented foods can dramatically increase the number of bacteria you get through your diet. As I’ll get to later, this can be both a good and a bad thing.
But what about sauerkraut specifically? Do we know how many bacteria that are present in a jar of sauerkraut? Some time ago, the famous health guru Dr. Mercola sent his sauerkraut off to a lab for analysis. Here’s what that the site NourishingPlot.com had to say about the results of that analysis:
Dr. Mercola sent his sauerkraut off to a lab and reported the findings of probiotics saying, “We had it analyzed. We found in a 4-6 ounce serving of the fermented vegetables there were literally ten trillion bacteria.” That means 2 ounces of home fermented sauerkraut had more probiotics than a bottle of 100 count probiotic capsules. Translated this means one 16 ounce of sauerkraut is equal to 8 bottles of probiotics. (2)
That’s pretty crazy to think about… According to this test, just 2 ounces (about 60 grams) of sauerkraut contain more bacteria than a jar of probiotic capsules!
Perhaps needless to say, the amounts of bacteria that are present in sauerkraut will depend on a range of factors, including fermentation method (the sauerkraut Dr. Mercola tested was produced with the use of a probiotic starter culture), fermentation time, the amount of salt used, and fermentation temperature. Also, it’s important to point out that this test, initiated by Dr. Mercola, isn’t necessarily 100% valid. It may be that some of the measurements are slightly off or that some things got lost in translations. That said, I think it’s safe to say that sauerkraut is filled with bugs!
– Question 2: What types of bacteria are present in sauerkraut?
It’s not just the quantity of bacteria that’s important, but also the diversity… This leads us over to the first sub-question posed earlier, which was: What types of bacteria are present in sauerkraut?
A 2007 study answers exactly that question. It examined the microbiota of commercial sauerkraut fermentations and found the following:
Previous studies using traditional biochemical identification methods to study the ecology of commercial sauerkraut fermentations revealed that four species of lactic acid bacteria, Leuconostoc mesenteroides, Lactobacillus plantarum, Pediococcus pentosaceus, and Lactobacillus brevis, were the primary microorganisms in these fermentations. In this study, 686 isolates were collected from four commercial fermentations and analyzed by DNA fingerprinting. The results indicate that the species of lactic acid bacteria present in sauerkraut fermentations are more diverse than previously reported and include Leuconostoc citreum, Leuconostoc argentinum, Lactobacillus paraplantarum, Lactobacillus coryniformis, and Weissella sp. The newly identified species Leuconostoc fallax was also found. (3)
Below is a figure showing the major types of bacteria that are present in commercial sauerkraut fermentations.
As you can see, the microbiota changes during the fermentation process. Different types of microbes dominate at different stages, which is to be expected, as the oxygen levels and pH of the ferment change during the fermentation process. Different microbes are adapted to different conditions and their reproductive fitness will therefore depend on the conditions of the space they find themselves in.
Keep in mind: the bacteria shown in the figure above are not the only types of bacteria that are present in sauerkraut. Other microbes are present as well, albeit in lower concentrations. Also, it should be noted that the microbiota of homemade sauerkraut differs somewhat from that of mass-produced sauerkraut. Many of the same types of bacteria dominate in homemade ferments, but the structure and diversity of the microbial ecosystem differ somewhat.
– Question 3: Do all of the bacteria that are present in sauerkraut survive past the stomach acid, and do they all colonize the gut?
The bacteria that are present in sauerkraut and other fermented foods are adapted to live in low pH conditions, and many (probably most) of them survive past the stomach acid (1). As for the second question, the short answer is no! Most of the microbes that are found in fermented foods tend to be transient; that is, they only pass through the digestive system, they don’t colonize it. That said, some of the bacteria found in sauekraut and other fermented vegetables are probably able to set up shop in the lower gut. Not all, but some!
This is the main reason why I recommend to eat a wide diversity of homemade, fermented vegetables. Each batch of fermented vegetables has a unique microbiota composition. By eating several different types, you increase the likelihood that you’re ingesting microbes that are able to colonize your gut.
Before we wrap up, I want to loop back to the thing I mentioned earlier about the pros and cons of the high concentrations of bacteria that are present in sauerkraut. The fact that fermented vegetables are packed with bacteria can be both a good and a bad thing. The good thing is that the consumption of fermented vegetables can bring a lot of potentially beneficial microbes into the lower gut. The bad thing is that (excessive) consumption of fermented vegetables may destabilize the gut microbiota, hindering the development of a stable, resilient ecosystem.
This is one of the reasons why my general recommendation is to occasionally eat small quantities of a diversity of fermented vegetables. More isn’t necessarily better. I don’t think it’s a good idea to eat large quantities on a daily basis. That said, there’s a lot of inter-individual variability with regards to how much fermented vegetables that can be consumed without ill-effects. Some people have a higher tolerance than others. The health status and microbiota composition of the individual have to be taken into account when an appropriate intake level is to be determined.