Fermented Foods

What are fermented foods?

Fermented foods are foods and drinks made by friendly microbes that turn natural sugars into acids or gases. This changes the taste, helps preserve the food, and can add live cultures that may support gut health [1].

At a glance

• What it means: Foods transformed by microbes like bacteria or yeast
• Why it matters: Can be tasty, longer lasting, and a source of live cultures
• Common examples in the UK: Yoghurt, kefir, cheese, sourdough bread, sauerkraut, kimchi, miso, tempeh, kombucha, pickled vegetables made by fermentation

How fermentation works in food?

Microbes eat the natural sugars in food and make acids or gases [2]. The acids give a tangy flavour and help stop harmful microbes growing. Some fermented foods still contain live cultures when you eat them. Others are cooked or pasteurised, which kills most live cultures but keeps the nutrition and flavour.

Fermented foods vs pickled foods: which is better?

Not all sour foods are fermented. Traditional pickling uses vinegar added to the food [3]. Fermented pickles make their own acids during fermentation [4]. Both can be part of a healthy diet. If you want live cultures, look for labels that say “raw,” “unpasteurised,” or “contains live cultures.”

What are the potential advantages of eating fermented foods?

• Gut support: Some fermented foods contain live cultures that can help keep the gut microbiome diverse [5].
• Digestibility: Fermentation can break down parts of foods, which may make them easier to digest for some people [6].
• Nutrients: Fermentation can create helpful compounds and may make certain nutrients more available.
• Food safety and storage: The acid made in fermentation helps preserve food safely when it is prepared and stored correctly.

Effects vary by product and person. Fermented foods are not a cure for medical conditions.

What is the most common fermented food?

Type of fermented food	Tips
Yoghurt and kefir	Choose plain yoghurt with live cultures. Add fruit for sweetness. Kefir is a drinkable cultured milk. Start with small servings if new to it.
Cheese	Hard and soft cheeses are fermented but most do not contain live cultures by the time you eat them. Enjoy as part of balanced meals. Watch portion size and salt.
Fermented vegetables	Sauerkraut and kimchi are cabbage based and naturally tangy. Look for chilled versions that say “live” or “unpasteurised” if you want active cultures.
Sourdough bread	Made with a starter of wild yeast and bacteria. Bread is baked so it will not contain live cultures, but people enjoy the flavour and texture.
Soy ferments	Miso and tempeh add savoury flavour and plant protein. Miso and tempeh add savoury flavour and plant protein. Miso is often used in soups. High heat reduces live cultures but keeps flavour.
Kombucha	Fermented tea that is naturally fizzy and sour-sweet. Can contain small amounts of alcohol from fermentation. Not suitable for children or pregnancy if unpasteurised.

Who should be cautious with fermented foods?

• Pregnancy and breastfeeding: Choose pasteurised products and follow standard food safety advice.
• Weakened immune system: Speak to a healthcare professional before using unpasteurised ferments with live cultures.
• Allergies and intolerances: Check labels for milk, soy, gluten, or fish products used in some ferments.
• Histamine sensitivity or certain gut conditions: Fermented foods can be high in histamine and may not suit everyone.
• Salt intake: Many fermented foods are salty. Balance portions if you are watching your blood pressure.
• Alcohol content: Some drinks like kombucha may contain trace alcohol. Not for children and avoid if you need to stay alcohol free.

Portion guidance

Yusra says: small amounts are enough. Try one small serving per day, such as:

• 125 g pot of live yoghurt
• 150 ml kefir
• 2 tablespoons sauerkraut or kimchi with meals
• 1 slice of sourdough bread
• 1 cup of miso soup

Increase slowly and listen to your body. Some people notice bloating at first which often settles.

Label reading made simple

• Look for “live cultures,” “raw,” or “unpasteurised” if you want active microbes.
• Check salt and sugar on the nutrition label.
• Scan the ingredients for allergens like milk or soy.
• For kombucha, check whether it is pasteurised and note alcohol warnings.

Storage and food safety

• Keep chilled products in the fridge and use within the date shown.
• Use clean utensils to avoid contamination.
• If smell, texture, or taste seems off, do not eat it.
• Homemade ferments need careful hygiene. If you are unsure, choose shop bought options made to UK safety standards.

Simple ways to add fermented foods

• Stir yoghurt into porridge or serve with berries.
• Add a spoon of sauerkraut next to grilled fish or a baked potato.
• Use miso to season soups and dressings off the heat.
• Swap a snack for a small glass of kefir.
• Enjoy sourdough toast with eggs and tomatoes.

Frequently asked questions

Are fermented foods the same as probiotics?

Some fermented foods contain live cultures, which can act like probiotics. Not all ferments meet the strict definition of a probiotic [7]; many are pasteurised. They can still be part of a healthy diet.

Do I need supplements if I eat fermented foods?

Most people can get what they need from a balanced diet rich in plants, fibre, and fermented foods if they enjoy them [8]. Supplements may be useful in some cases. Speak to a pharmacist, dietitian, or your doctor if unsure.

Can children eat fermented foods?

Yes, many are safe for children [9], such as live yoghurt. Avoid unpasteurised products and drinks with alcohol content.

Nutritionist's Corner: Final Thoughts

“Fermented foods can be a simple way to support a varied, tasty diet. Start small, choose products with clear labels, and focus on overall balance with plenty of plants and fibre. If you have allergies, are pregnant, or have a medical condition, pick pasteurised options and seek advice when needed. Enjoy them as part of meals rather than looking for quick fixes.”

— Yusra Serdaroglu Aydin, MSc RD

Vivere helps you take control of your health with personalised insights from state-of-the-art gut microbiome testing, nutritional guidance, science-backed supplements such as NAD+ shots and expert support. Sign up today and start living better, for longer.

Medical disclaimer

This page is for general information. It is not a substitute for personalised medical advice. If you have a health condition, take medicines, are pregnant, or care for a child, speak to a healthcare professional for guidance that fits your needs.

Sources

[1] Fermented foods can add depth to your diet - Harvard Health Publishing

[2] An overview of fermentation in the food industry - looking back from a new perspective - PMC

[3] Sudhanshu S. Behera, Aly Farag El Sheikha, Riadh Hammami, Awanish Kumar, Traditionally fermented pickles: How the microbial diversity associated with their nutritional and health benefits?, Journal of Functional Foods, Volume 70, 2020, 103971, ISSN 1756-4646, https://doi.org/10.1016/j.jff.2020.103971.

[4] Alan Y. Culture fermentation of Lactobacillus in traditional pickled gherkins: Microbial development, chemical, biogenic amine and metabolite analysis. J Food Sci Technol. 2019 Aug;56(8):3930-3939. doi: 10.1007/s13197-019-03866-8. Epub 2019 Jun 11. PMID: 31413418; PMCID: PMC6675860.

[5] Leeuwendaal NK, Stanton C, O'Toole PW, Beresford TP. Fermented Foods, Health and the Gut Microbiome. Nutrients. 2022 Apr 6;14(7):1527. doi: 10.3390/nu14071527. PMID: 35406140; PMCID: PMC9003261.

[6] Fermented foods can add depth to your diet - Harvard Health Publishing

[7] Do fermented foods contain probiotics? - ISAPP

[8] How — and why — to fit more fiber and fermented food into your meals - Harvard Health Publishing

[9] Fermented Food Guidelines for Children - Pediatrics Research Journal