Under the Microscope: The Science of Bioavailability

Find out how fermentation helps aid your digestive system absorb more nutrients from grains, seeds, and legumes.

| Winter 2019


Fermentation enthusiasts tend to talk a lot about the nutritional benefits of fermented foods. After all, in addition to the nutrients of the original ingredients, there are all those beneficial microbes and the products of their metabolic processes. Essentially, fermentation microbes enhance nutrition because they increase the bioavailability of nutrients present in grains, seeds, and legumes.

Bioavailability is a measure of how easily your body can absorb a particular nutrient, such as iron, or vitamin C. If a nutrient has a high bioavailability, it means you’ll be able to absorb more of that nutrient when you eat the food containing it, while low bioavailability means your body will struggle to extract that nutrient from your food. For example, you may have heard that if you’re trying to increase your blood iron levels, you should avoid consuming dairy with your iron-rich steak and spinach. This is because calcium tends to bond with iron in foods to create new molecules that your body can’t readily absorb; thus, calcium decreases the bioavailability of the iron.

Getty Images/RuslanDashinsky

Grains, seeds, and legumes are packed with micronutrients — including  essential amino acids — and minerals, but like many other plant-based foods, most of that nutrition is locked up tightly in the cellulose structures of plants, which our bodies break down inefficiently, if at all. In addition to structural barriers, plant-based foods tend to be fairly high in phytic acid, which is prone to bonding with metals — such as iron, zinc, and calcium, as well as amino acids — rendering these essential minerals already lacking in our diets, even more inaccessible. With an advantage over humans, ruminants and other multi-stomached animals often have phytase enzymes in their digestive tracts, which allow them to break down plant structures, helping to extract the nutrients inside more easily.

But for humans, fermentation helps increase the bioavailability of nutrients in plant-based foods, in part, because the microbes break down the cellulose fibers of plants by consuming the glucose and other simple sugars that comprise them. Fermentation also tends to lower the pH of plant-based foods, making them more acidic over time, which allows the phytic acid to chemically release the iron, zinc, calcium, and amino acids that tend to bond with it. With cellulose fibers structurally broken down and phytic acid unbound from these nutrients, our intestines can absorb the healthy compounds from plant-based foods at much higher rates than they would if we were to eat unfermented versions of the same foods.

Adobe Stock/Rudolf Hein

Cultures around the world, many of which rely on plant-based diets, have taken advantage of the doubled benefits of fermented grains, seeds, and legumes, from dosa made with fermented rice and lentil batter; to tofu, miso, and soy sauce made with fermented soybeans; to injera made with fermented teff grains; and many other regional ferments. The fermentation process extends the shelf life of softer grains and beans, and increases the bioavailability of crucial nutrients across the board, to support better health even when food options are limited.



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