Depending on your tastes, you may find that many of your favourite foods are products of fermentation. Wine, cheese, bread, beer, and chocolate are just a few of these products that humans have enjoyed for thousands of years thanks to this simple chemical process. What started as a food preservation technique has now become a trendy way to modify the taste, texture, and health benefits of all types of food and beverages.
Fermentation involves the conversion of sugars to alcohols and organic acids using microbes like bacteria and yeasts. For example, the yeast used in winemaking turns the sugar in grape juice into ethanol and carbon dioxide as a by-product.
As early as 10,000 BCE, humans took advantage of the spontaneous fermentation that occurred in milk from early domesticated animals, creating nutrient-dense and long-lasting dairy products. The discovery of beer residues from this time period led scientists to find the world’s first brewery in a cave in Israel. Other fermented beverages were being brewed as well, such as a nine-thousand-year-old drink made by a Neolithic culture in China using fruit, rice, and honey.
The use of fermentation quickly expanded to other foods: bread made by Egyptians in 3500 BCE, pickles made by Mesopotamians in 2000 BCE, kombucha made by the Chinese in 200 BCE, and fermented corn drinks like tejuino made in pre-Hispanic Mexico. It wasn’t until 1856 when Louis Pasteur discovered forces he called “ferments”, what we know today as the catalytic action of yeast metabolism, that we began to understand fermentation as a process of life, not death. Further advances in microbiology helped to turn fermentation into an industrial process. New techniques in food science have refined the composition of microbes used in fermentation and led to entirely new food products like the Impossible Burger.
Once a necessary method of food preservation, many now know “fermented” as a word used by food companies to promote their products. But do fermented foods have any real health benefits? The answer is: possibly.
Consuming fermented foods could be beneficial by improving the nutritional value of the food, or by modulating the gut microbiome to prevent disease. Analyzing the nutritional properties of fermented foods is relatively straightforward, however, very few randomized clinical trials (RCTs) have investigated whether consuming fermented foods improves disease resistance.
There is some evidence to suggest that fermentation increases the vitamin content of some foods. Tempeh, a traditional Indonesian food made from fermented soybeans, is enriched for vitamin B12, a vitamin predominantly found in animal products, making it an excellent option for people with plant-based diets who have an increased risk of vitamin B12 deficiency. Yoghurt has additional folate (vitamin B9) compared to unfermented milk, and often possesses different riboflavin (vitamin B2) levels. Whether the riboflavin content is higher or lower than unfermented milk depends on the microbial abundance and diversity in the starter culture that’s used.
Some studies have focused on the antihypertensive and antidiabetic properties of fermented foods. Whole wheat sourdough bread has been developed using a specific strain of Lactobacillus that produces functional antihypertensive peptides, while other studies have shown that sourdough has a lower glycemic index than other breads.
The best-described health benefit of fermented foods, though, is the antioxidant activity that fermentation enhances. Oxidative damage has been linked to many age and diet related diseases like Alzheimer’s disease and stomach cancer, but the body can shield itself from this damage using enzymes like peroxidases and other compounds like vitamin C and carotenoids. Several studies have found that fermented foods, especially fermented milk, have higher antioxidant activity than similar unfermented products. Several factors affect the antioxidant potential of fermented milk, including the milk origin (goats’ milk has greater potential than camels’ or cows’ milk when fermented), fat content (fat-free yoghurt has greater potential than semi and full-fat yoghurts), and fermenting microbe strain (some species of lactic acid-producing bacteria confer greater potential than others). Similar antioxidant effects are described in fermented quinoa and fermented apple juice.
Many fermented food products are advertised as probiotic foods that improve gastrointestinal health by modifying the gut microbiome. While these labels are good for marketing, they are somewhat misleading. A 2021 statement by the International Scientific Association for Probiotics and Prebiotics (ISAPP) called much of the information on fermented foods presented by social media “exaggerated or inaccurate”. This is due to the lack of evidence presented by the food industry that their fermented products have consistent probiotic properties. For this to be the case, live microorganisms that can colonize the gut need to be sufficiently present in the product. However, with the many types of fermented foods available with different manufacturers and different starter cultures, these conditions are not always present in fermented foods. Furthermore, any probiotic effect from fermented foods is not clinically proven to have health benefits to the consumer, as results from the RCTs on fermented foods and probiotics are mixed.
The main issue when it comes to studying the health benefits of fermented foods is the inherent mosaicism that makes up the category of fermented food. These foods have different manufacturers, animal and plant origins, industrial processes, and, most diverse of all, the microorganisms used in the fermentation process. It’s difficult to precisely control the abundance and diversity of these microbes, which in turn affects the beneficial effects of the final product.
The explosion of interest in fermented foods can be attributed to the food industry’s marketing of these products as superfoods and consumers’ growing interest in improving their diet by natural means. While early studies on the nutritional benefits and probiotic characteristics of fermented foods are promising, most of the claims peddled by food manufacturers are overstated. Research still needs to move beyond chemical analysis of fermented foods and animal models towards the analyses of existing health databases and placebo-controlled RCTs with well-characterized microbe strains and nutrient compositions. But just like scientists, consumers are still getting to know how the microbiome works, and with more research fermented foods may one day be recommended as their own food group as part of a healthy diet.
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