When it comes to nutrient-dense carbohydrates, root vegetables are hard to beat - Foods like sweet potatoes, carrots, and cassava are not only delicious, but they're also a great source of vitamins, minerals, phytochemicals, and fiber. Fortunately for root lovers, these veggies also have another major benefit - they are a total boon to our gut microbiota.
Root vegetables are great for the gut microbiota
Many root vegetables have powerful prebiotic properties, as they feed the beneficial bacteria in our colon and support a healthy composition of gut microbes
Let's take a look at the unique ways root vegetables help support a healthy community of gut critters.
Bifidobacteria and lactobacilli increase
Root vegetables contain a variety of carbohydrates that feed two major groups of probiotic bacteria: Bifidobacterium and Lactobacillus.
Bifidobacteria perform a myriad of functions, including vitamin production, preventing pathogens from colonizing the intestinal mucosa (including E. coli), protecting against yeast overgrowth, improving intestinal barrier function, and reducing intestinal endotoxin transport.
Additionally, lactobacilli (including the most widely used probiotic, Lactobacillus acidophilus) help inhibit the growth of pathogens such as H. pylori (through a process called "competitive exclusion"), and some species have anticancer and antidiabetic effects.
Basically, these bacteria are essential probiotic residents of a healthy gut, so making decisions that support their growth is very important.
And root vegetables are proven promoters of these amazing microbes. In a study that used an in vitro fermentation system in conjunction with human fecal slurry, two different varieties of sweet potato significantly increased Bifidobacterium levels over the course of 24 hours.
In addition, cassava (a starchy root that is also a source of tapioca) has been shown to stimulate the growth of bifidobacteria and lactobacilli.
A study of oligosaccharides released from cassava pulp showed that levels of Lactobacillus gasseri, which has significant anti-inflammatory activity, and Bifidobacterium breve, which can potentially improve fat metabolism and skin health, increased dramatically, as at the same time that Lactobacillus reuteri (which produces vitamin B12 and folic acid), Lactobacillus acidophilus (which helps restore the microbiota after antibiotic treatment) and Bifidobacterium adolescentis (which reduces the mineral-binding effects of phytic acid) increased to varying degrees.
In rats, food crackers containing cassava fiber and wheat flour (in proportions of 60:40 or 50:50) resulted in an increase in the Lactobacillus count, and in mice, xylooligosaccharides derived from cassava feces (another by-product of cassava starch processing) were also shown to promote the growth of Bifidobacterium and Lactobacillus species.
Several other studies showed that Jerusalem artichokes were able to improve the levels of various Lactobacillus and Bifidobacterium species in a variety of animals, due to their high concentration of fructooligosaccharides (or FOS), a subtype of inulin that is not digested in the gut. thin and serves as a powerful prebiotic for colon microbes.
Another vegetable rich in FOS are yacon (a slightly sweet tuber native to the Andes), and animal studies have also shown that a diet rich in yacon or yacon flour enhances the growth of bifidobacteria and lactobacilli.
A study of rats found that within a week of eating a diet containing 10% yacon root, the intestinal environment was significantly altered due to the abundant fermentation of yacon, leading to a significant increase in Lactobacillus acidophilus, Bifidobacterium pseudolongum and Bifidobacterium animalis.
Some yacon crops contain up to 70% fructooligosaccharides on a dry matter basis, so it's no surprise that this root vegetable is an effective prebiotic.
Root vegetables increase SCFA production
Short-chain fatty acids or SCFAs, including butyric acid, acetic acid, and propionic acid, are produced from the fermentation of fiber by specific groups of bacteria in the gut.
In addition to serving as the main food source for intestinal epithelial cells, SCFAs offer a huge list of benefits to our health, including reducing the risk of inflammatory diseases, protection against obesity and diabetes, and the risk of disease from the heart.
And, it so happens that the carbohydrates that are fermented in SCFA are found abundantly in most root vegetables, such as pectin, rich in carrots; fructooligosaccharides that are abundant in Jerusalem artichokes, burdock root, chicory root, and yacon; and resistant starch in the form of RS3 (high content in cassava and cooked and cooled potatoes).
In vitro, orange-fleshed sweet potato purees were shown to increase butyric acid production when fermented by human fecal bacteria.
In rodents, diets supplemented with yacon or yacon flour have been shown to increase SCFA levels. Rats fed a diet containing 6% fructooligosaccharides and yacon inulin experienced beneficial modulation of the gut microbiome, including a significant increase in butyrate levels.
Another study of rats found that a week-long diet containing 10% yacon root led to SCFA production that was 70% higher than when fructooligosaccharides were used alone, suggesting that the non-FOS components of yacon were also fermented. at SCFA.
And, when it comes to SCFA, potatoes deserve a special mention. Potatoes that have been cooked and cooled to create retrograde resistant starch have been shown to significantly increase SCFA production, as has raw potato starch.
And, continued consumption of resistant starch from potatoes appears to reshape the microbiota over time to generate even more SCFA.
In a rat study, for example, resistant potato starch had a butyrogenic effect that increased over time, and butyrate production increased six times after six months of consumption compared to half a month of consumption.
That suggests a slow adaptation process that occurs within the gastrointestinal tract and is a strong case for consistently including resistant starch in our diets for maximum benefit from SCFA production.
Reduce infection by pathogens
As a result of altering the gut environment, root vegetables can help prevent pathogens from colonizing and infecting the gut.
In mouse research, cassava fiber-supplemented grain products resulted in lower levels of Escherichia coli in animal feces, while promoting a greater abundance of probiotic bacteria, suggesting an ability to selectively suppress the growth of some pathogens while allowing the "good guys" "to flourish.
In mice, components of cassava root were also shown to decrease the number of Escherichia coli present.
And, some root vegetables contain compounds other than fiber that suppress the growth of pathogens. Yacon, for example, contains natural antimicrobial substances, as evidenced by the fact that yacon crops require almost no pesticides to grow.
Some of these substances have antibacterial activity not only against plant pathogens, but also against those known to infect humans, such as Bacillus subtilis and Staphylococcus aureus.
An experiment with mice even showed that yacon flour could prevent intestinal infection by Salmonella enterica serovar Typhimurium (S. Typhimurium), due to its ability to enhance non-specific immunity and improve the intestinal immune barrier.
Even carrots contain compounds that reduce the growth of pathogens. In one experiment, extracts from peeled and grated carrots were able to inhibit a variety of harmful bacteria including Listeria monocytogenes, Staphylococcus aureus, Pseudonomas fluorescens, Candida lambica, and Escherichia coli.
Improves the Bacteroidetes / Firmicutes ratio
In multiple studies, the ratio of Bacteroides to Firmicutes (two main phyla bacteria) has been correlated with obesity, with a higher ratio (more Bacteroidetes) associated with thinness, and a lower ratio (more Firmicutes) associated with greater body fat.
In immunosuppressed mice, three purple sweet potato polysaccharides increased the relative abundance of Bacteroidetes while reducing Firmicutes levels, helping to move the microbiota in the direction associated with leanness.
So, long live root vegetables! In case we need more reasons to add these delicious, versatile and nutrient-packed veggies to our diet, we can do it for our gut