Since both founders here at The Crafty Pickle Co. are nutritionists we stay close to the current evidence on living fermented foods like ours. Looking back on last year we've picked out some of the most interesting and compelling research from 2023 looking at different types of fermented foods. In this blog we've helpfully digested it so that you don't have to read through whole research papers (man can they be dry!).
Scientific research is the best way we have to understand the links between foods and our health, however fermented foods like ours are notoriously understudied, so this is an emerging field. It's also important to note that studying people is difficult because we lead complicated lives and don't like to be told what to do that much! So all of this latest research just gives us an indication of the possibilities of what these foods do. We've also only included human studies, as lots of the initial testing phases happen in lab or animal studies. However, these are really only important for scientists to direct future research and aren't useful for interpretation to human health.
Yoghurt & Cheese
The vast majority of the research into fermented foods has been done using yoghurt and cheese, two of the most commonly consumed fermented foods in the UK. Although not all cheese contains living microbes many cheeses which have been aged but not then heated do, such as parmesan, cheddar, gouda and edam.
A systematic review and meta-analysis (SRMA) which groups lots of studies together to analyse the strongest evidence found that in this study fermented dairy (1):
Was associated with a significantly decreased risk of depression (a reduction on average of -11%)
This link was specifically found when cheese and yoghurt were consumed.
Authors speculate that there may be some association with fermented dairy intake and depression here due to the gut-brain axis.
Milk Kefir
Milk kefir, a fermented drink made using a collection of bacteria and yeasts called a SCOBY is also fairly well studied. However, although there have been several new studies released recently there's still many more looking at other types of fermented dairy products. Three new studies from 2023 show us the following:
1. In a small study of 26 adult volunteers (2), compared to a control drink milk kefir (which contained 25-30 billion microbes):
Significantly increased Lactobacillus species in poop samples
Significantly improved performance on 2 metrics of memory
2. In a systematic review of human intervention trials on kefir and health (3) milk kefir was found to potentially:
Be useful as a complementary therapy to reduce risk of dental caries
Be useful as a complementary therapy in Helicobacter pylori eradication.
Help to improve blood lipid profile and hypertension.
Authors recognise the lack of data on safety and efficacy from the currently available evidence however.
3. A SRMA of human intervention trials of kefir and cardiometabolic risk factors (4) (those related to heart and metabolic health) found that milk kefir intake:
Significantly reduced fasting insulin and measures of insulin resistance
But had no significant effect on other markers such as blood cholesterol and triglycerides.
Fermented foods in general
Lots of studies have looked at the health effects of regularly consuming a wide variety of fermented foods. These can sometimes be more helpful as they tell us about different dietary patterns and how they can impact us. This is useful as it more closely reflects normal daily life where we eat a wide variety of different foods over time, not just huge quantities of specific foods for a short time. Three systematic reviews released in 2023 found the following.
1. A SRMA looking at the effects of consuming fermented foods (mostly fermented milk) on diarrheoal disease in children aged under 5 found that it (5):
Significantly reduced the mean duration of diarrhoea, however this was only by an average of half a day.
Significantly reduced the length of hospitalisation by a third of a day.
Had no significant effect on stool frequency.
2. A systematic review of studies looking at the link between fermented food and drink intake and neurodegenerative decline in old age found that the following products were associated with beneficial changes to the brain that may result in lower risk of dementia and Alzheimers (6):
From 1-3 drinks per day of beer and 1-4 drinks per day of wine
From 1-6 cups of coffee per day
Daily intake of fermented soy
And varied, balanced dietary patterns which include daily intake of fermented foods.
The authors are quick to point out that these associations do not imply causation and that not all studies agreed, particularly when it came to alcohol. Therefore, this definitely does not show that drinking more improves cognitive health!
3. Another SRMA of 18 randomised controlled trials (RCT) in a total of 843 people with type 2 diabetes (T2D) or at risk of T2D, looked at fermented food intake and metabolic outcomes (7). This study found that fermented foods versus controls gave a:
Significant reduction in fasting blood glucose and insulin resistance
Significant reduction in blood lipoproteins including triglycerides, LDL cholesterol
Significant reduction in diastolic blood pressure
4. A small RCT in 45 adults gave participants either a 'psychobiotic' diet (one high in fermented foods and prebiotics) or a control diet (8). They found:
Only subtle changes in the microbial composition of participant's poop
The psychobiotic diet gave greater reductions in measures of subjective stress (-32% vs -17%). This effect was dose dependent, so those sticking to the diet the best had the greatest reductions in perceived stress.
Authors highlight that much more research needs to be done to further tease out effects of dietary changes on affect mood and to determine why this might be happening.
A further study which wasn't done in humans but which we found interesting was an analysis of 47 fermented foods available in Sweden (9). They looked at the microbial composition in terms of what bacteria are within them, they found that:
Lactic acid bacteria (those found in kraut and kimchi) and acetic acid bacteria (like those found in kombucha) dominated most samples.
Each type of fermented food had a unique composition.
Kombucha and water kefir had the highest diversity of microbes
S.thermophilus was abundant in yoghurts, which makes sense as this is one of the bacterial species added to milk to ferment it into yoghurt.
Lactococcus lactis was abundant in milk kefir, this has been studied for its probiotic properties
Lactiplantibacillus plantarum was commonly found in kimchi, kraut and fermented cucumbers. This species is also associated with health benefits in humans.
What does it all mean?
It's really important to remember that single studies rarely to never tell us anything that we could then use to directly inform our health. Even intervention trials in humans tend to be done on just a few individuals, so it's really difficult to draw conclusions about the wider population within the context of our complicated, messy lives. There's a lot more work to be done to truly unravel the interactions between fermented foods and health but for now most of the evidence is showing that they're safe and can be supportive of health for the vast majority of us,. They do this by helping to re-build the microbial diversity of our diets which can potentially help support our gut microbiome which we're beginning to understand is truly essential for health and life.
References
1 Luo et al. (2023). Fermented dairy foods consumption and depressive symptoms: A meta-analysis of cohort studies. PLoS One. 18(2):e0281346. doi: 10.1371/journal.pone.0281346.
2 Cannavale et al. (2023). Consumption of a fermented dairy beverage improves hippocampal-dependent relational memory in a randomized, controlled cross-over trial. Nutr Neurosci. 26(3):265-274. doi: 10.1080/1028415X.2022.2046963.
3 Kairey et al. (2023). The effects of kefir consumption on human health: a systematic review of randomized controlled trials. Nutr Rev. 81(3):267-286. doi: 10.1093/nutrit/nuac054.
4 Yahyapoor et al. (2023). Effects of Kefir Consumption on Cardiometabolic Risk Factors: A Systematic Review and Meta-analysis of Randomized Controlled Trials. Curr Drug Targets. 24(7):599-612. doi: 10.2174/1389450124666230427095742.
5 Olayanju et al. (2023). The efficacy of fermented foods in the treatment and management of diarrhoeal diseases: A systematic review and meta-analysis. Nutr Health. 29(1):71-83. doi: 10.1177/02601060221095678.
6 Porras-García et al. (2023). Potential neuroprotective effects of fermented foods and beverages in old age: a systematic review. Front Nutr. 10:1170841. doi: 10.3389/fnut.2023.1170841.
7 Zhang et al. (2023). Fermented foods and metabolic outcomes in diabetes and prediabetes: A systematic review and meta-analysis of randomized controlled trials. Crit Rev Food Sci Nutr. 1-18. doi: 10.1080/10408398.2023.2213770
8 Berding et al. (2023). Feed your microbes to deal with stress: a psychobiotic diet impacts microbial stability and perceived stress in a healthy adult population. Mol Psychiatry. 28(2):601-610. doi: 10.1038/s41380-022-01817-y.
9 Palmnäs-Bédard et al. (2023). Characterization of the Bacterial Composition of 47 Fermented Foods in Sweden. Foods. 12(20):3827. doi: 10.3390/foods12203827.