When it comes to nutrient-dense carbs, root veggies are hard to beat: foods like sweet potatoes, carrots, and cassava are not only delicious, they’re also great sources of vitamins, minerals, phytochemicals, and fiber. (Be sure to check out my posts The Case for More Carbs: Insulin’s Non-Metabolic Roles in the Human Body, How Many Carbs Should We Eat?, Paleo, Resistant Starch, and TMAO: New Study Warning Worth Heeding, 5 Weird Root Vegetables Everyone Needs to Try, The Health Benefits of the Parsley Veggie Family and Potatoes: Friend or Foe?).
Root vegetables are any underground plant part consumed as vegetables, though not all of them are “true” roots. (Botanically, bulbs like onions, corms like taro, rhizomes like ginger, and tubers like potatoes aren’t actually roots, but in the culinary world, they all count!) Root vegetables originate from all around the globe, and were one of the earliest foods consumed by humans: archaeologists discovered evidence of cooked starchy roots dating back 170,000 years in a cave in South Africa! Even today, in many parts of the world, root vegetables are more important as a staple food than grains, especially West and Central Africa and Oceana. This due to both their versatility and their ability to store without spoiling for long periods after being harvested.
Although the full list of root vegetables numbers in the dozens, in this post, we’ll be looking specifically at starchy root vegetables, including:
- Potatoes (also discussed in Potatoes: Friend or Foe?)
- Sweet potatoes
- Yams (yep, they’re not the same as sweet potatoes! Even though “yam” is often used interchangeably with “sweet potato,” they actually belong to an entirely different plant family, and are distinguished by their rough, bark-like skin)
- Jerusalem artichoke
- Cassava (also known as yuca)
(You can read more about carrots and parsnips in my article on the parsley family!)
Root Veggies Are Nutrient-Dense
Nutritionally, root vegetables vary in their nutritional composition, but due to their role as storage organs (storing nutrients and energy for the rest of the plant), they tend to be rich in slow-burning carbohydrates and micronutrients. (See The Case for More Carbs: Insulin’s Non-Metabolic Roles in the Human Body, How Many Carbs Should We Eat?, and The Importance of Nutrient Density)
Potatoes, for example, are much more nutrient-dense than many people realize! One medium baked potato contains 160 calories, 3.8 grams of fiber, about a quarter of the DV for vitamin C, potassium, vitamin B6, and manganese, and notable amounts of magnesium, phosphorus, niacin, and folate, copper, and iron; it also contains smaller amounts of zinc, calcium, thiamin, pantothenic acid, and riboflavin. (Potatoes that have been cooked and cooled are also a notably high source of retrograded resistant starch (RS3), while raw potato starch is high in RS2.)
Likewise, one medium sweet potato contains 103 calories, 3.8 grams of fiber, and a whole lot of nutrition—including 438% of the DV for vitamin A, 37% of the DV for vitamin C, 28% of the DV for manganese, and plenty of vitamin B6, pantothenic acid, copper, niacin, thiamin, and magnesium. It also has smaller amounts of vitamin E, riboflavin, folate, calcium, iron, phosphorus, and zinc! This is on top of the wide range of polyphenols sweet potatoes contain (and which give them their beautiful colors), such as anthocyanins, carotenoids, and xanthophyll.
Other root veggies are great choices too! One medium turnip contains 34 calories, 2.2 g of fiber, 43% of the DV for vitamin C, and some B vitamins, calcium, manganese, potassium, and copper. One cup of rutabaga contains 50 calories, 3.5 g of fiber, 58% of the DV for vitamin C, 13% of the DV for potassium, 12% of the DV for manganese, and some B vitamins, calcium, magnesium, and iron. And, 100 grams of cassava contains 160 calories, 34% of the DV for vitamin C, 19% of the DV for manganese, and some potassium, copper, magnesium, folate, thiamin, niacin, and vitamin B6.
Root vegetables can support human health in a number of ways, with different veggies offering unique benefits (read: the wider the variety we eat, the better!).
For example, across numerous studies looking at different cultivars and components of sweet potato, this amazing tuber has also been shown to exhibit antioxidative, anti-inflammatory, anti-obesity, liver-protective, anti-aging, blood-sugar-lowering, and immunomodulatory properties. Both in vitro and in animal studies, purple-fleshed sweet potato has been shown to exert anti-cancer properties against colon tumors, and sweet potato anthocyanins have demonstrated protective activity against stomach cancer, breast cancer, and bladder cancer cells. Not only that, but sweet potatoes also show promise for enhancing cognitive performance and memory, in part by reducing inflammation and preventing free radical damage in the brain. In a mouse model of brain aging, supplementation with purple sweet potato color protected against cognition deficits, while also reducing oxidative damage and inflammation; sweet potato color also reduced brain inflammation in mice fed a high-fat diet (by inhibiting ERK, p38, JNK, and NF-κB activation). And, anthocyanin from purple sweet potato was able to enhance memory in rats!
Yams bring a host of benefits as well, including positive effects on brain function, cancer protection, diabetes, and even weight loss! Many of these benefits are related to its phytosteroid diosgenin, which has been shown to have significant hypoglycemic, antioxidant, anti-inflammatory, cholesterol-lowering, and anti-cancer properties (particularly against colon cancer, leukemia, squamous carcinoma, liver cancer, gastric cancer, breast cancer, and lung cancer cells). Where cancer is concerned, the diosgenin in yams has activity during multiple stages of tumorigenisis, helping modulate signaling events involved in cell differentiation, growth and proliferation, apoptosis, oncogenesis, and angiogenesis (including via p53 activation, caspase-3 activity modulation, and activation of the transcription STAT3 signaling pathway). Similarly, in a mouse model of colon cancer, eating diets containing either 2% or 5% yam powder protected against the formation of aberrant crypt foci (the earliest cancerous lesions found in colon cancer) by enhancing the antioxidant defense system and modulating inflammatory mediators such as NF-κB, inducible nitric oxide synthase, cyclooxygenase-2, TNF-α, and interleukin-1β. Yam may also help boost brain health: in a 12-week study of healthy adults, daily yam extract significantly improved cognitive function, and in mice, diosgenin from yam improved learning and memory abilities when undergoing maze tests. In a study of male rats, yam extract at fed at levels of 100 mg/kg, 200 mg/kg, and 300 mg/kg resulted in significantly lower food intake, lower blood sugar levels, and lower body weight, suggesting an appetite suppressive and blood glucose lowering effect.
Similarly, turnips have been show to exhibit anti-tumor, antidiabetic, antioxidant, anti-inflammatory, anti-hypertensive, nephroprotective, and hepatoprotective effects, largely via their bioactive compounds. The indole derivative arvelexin found in turnip has been shown to lower blood pressure and blood lipids, while also reducing inflammation. Phytonutrient-rich turnip extract was able to protect against liver toxicity in rats by reducing serum levels of glutamateoxaloacetate transaminase, glutamate pyruvate transaminase, bilirubin, and alkaline phosphatase. In a mouse model of type 2 diabetes, ethanol extract of turnip enhanced glucose and lipid metabolism, reduced lipid peroxidation, improved insulin tolerance, and lowered a number of important blood markers (glycosylated haemoglobin, insulin, glucagon, and C-peptide). In an obese mouse model, turnip extract was also able to suppress weight gain and fat accumulation without affecting food intake, and rats with fructose-induced metabolic syndrome saw a reduction in body weight, blood sugar levels, triglycerides, total cholesterol, and lipid peroxidation when treated with ethanolic turnip extract versus metformin. Alcoholic extracts of turnip have even demonstrated pain-relieving properties in mice!
Meanwhile, rutabagas are high in glucosinolates that possess antioxidant properties, and which have been shown to reduce inflammation and inhibit the growth of colorectal, breast, and prostate cancer cells. See also The Health Benefits of Cruciferous Vegetables
Eating cassava can also support our health in a few different ways. For one, it contains resistant starch, which has been shown to improve insulin sensitivity, increase satiety, lower the blood sugar response to meals, and promote feelings of fullness. Its vitamin C content gives it antioxidant potential and can support the immune system, and its manganese is important for bone production, blood sugar control, skin integrity, and the function of enzymes that protect the body from free radical damage.
And what about one of the most famous root veggies at all: the potato? There’s good news for those who tolerate nightshades! Although observational studies haven’t always painted potatoes in a good light, this is often due to the way they’re consumed (fried in vegetable oils, eaten as French fries with fast food meals, or munched on as potato chips). After adjusting for confounders, one study found that potatoes are associated with a reduced risk of total mortality (25% risk reduction). Likewise, some bioactive compounds in potato (including alpha-chaconine and gallic acid) have been shown to induce the death of some cancer cells, including prostate, colon, and liver. The resistant starch in potato can also help improve insulin sensitivity, boost satiety, decrease blood sugar levels, promote feelings of fullness, and reduce food intake. In fact, in a study of 38 different foods, boiled potatoes ranked highest on the satiety index! (For more on the pros and cons of potatoes, see Potatoes: Friend or Foe of Paleo?)
Root Veggies Are AMAZING for Gut Health
Luckily for us root lovers, these vegetables come with another major benefit as well: they’re a total boon for our gut microbiota! (See What Is the Gut Microbiome? And Why Should We Care About It?)
Root vegetables contain a variety of carbohydrates that feed beneficial species of bacteria in the gut, including being especially awesome at supporting the growth of two particularly important genera of probiotic bacteria: Bifidobacterium and Lactobacillus. Bifidobacteria carry out a huge number of roles, including producing vitamins, preventing pathogens from colonizing the gut mucosa (including E. coli), protecting against yeast overgrowths, improving the gut barrier function, and reducing endotoxin transport. Likewise, 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 anti-cancer and anti-diabetic effects. Basically, these bacteria are essential probiotic residents of a healthy gut, so it’s crazy important to make choices that support their growth! And, root veggies are well-proven promoters of these incredible microbes!
Along with containing fiber that enhances the growth of the beneficial bacteria, the prebiotics in root vegetables also enhance the production of short-chain fatty acids (SCFAs).
SCFAs (including butyric acid, acetic acid, and propionic acid) are produced from fiber fermentation by specific bacteria groups in the gut. Along with serving as the main food source for intestinal epithelial cells, SCFAs offer an enormous list of benefits for our health, including reducing the risk of inflammatory diseases, protecting against obesity and diabetes, and reducing the risk of heart disease. And, it just so happens that the carbohydrates that get fermented into SCFAs are found abundantly in most root vegetables, such as pectin (high in carrots), fructooligosaccharides (abundant in Jerusalem artichokes, burdock root, chicory root, and yacon), and resistant starch in the form of RS3 (high in cassava and cooked and cooled potatoes) (for more on resistant starch, including why RS3 may be superior to other resistant starch subclasses, see Resistant Starch: It’s Not All Sunshine and Roses!)
And finally, root veggies contain antimicrobial compounds that help prevent pathogens from colonizing the gut. Another awesome gut health benefit of root veggies!
Let’s take a closer look at the unique ways root vegetables help sustain a healthy community of gut critters.
Potatoes prepared in ways that create resistant starch (namely, cooking them and then refrigerating them before preparing them to eat [RS3], or supplementing with raw potato starch [RS2]) can be superfoods for the gut microbiota. This is because resistant starch is insoluble yet highly fermentable, and plays a major role in the generation of SCFAs by gut bacteria that consume it. (See Resistant Starch: It’s Not All Sunshine and Roses.)
In a human study, RS2 was shown to increase the abundance of Ruminococcus bromii and Eubacterium rectale. Long-term feeding of RS1 and RS2 in rats showed that both types increased the abundance of anaerobes, the levels of Bifidobacteria, and total SCFAs in the cecum; meanwhile, RS2 (but not RS1) enhanced levels of Lactobacillus, Streptococci, and Enterobacteria. Resistant potato starch had a butyrogenic effect that increased over time, with butyrate production increasing six-fold after six months of consumption compared to half a month of consumption. (That suggests a slow adaptive process occurring within the GI tract, and makes a strong case for consistently including resistant starch-rich root veggies in our diets for maximum SCFA-producing benefit!). In pigs, RS3 has been shown to increase the abundance of Faecalibacterium prausnitzii while reducing levels of E. coli and Pseudomonas species. Interestingly, Ruminococcus bromii plays a keystone role in the degradation of resistant starch, releasing breakdown products that are then utilized by other microbes in the gut.
Intriguingly, different sources of resistant starch can have significantly different impacts on SCFA production, and it turns out that RS3-containing root veggies may have some benefits over RS3-containing grains! This is because even within resistant starch subclasses, subtle variations in structure can influence the response of the microbiota. For example, depending on the food source they come from, the double-helix shape formed in retrograded resistant starch (RS3) results in crystalline entities with different shapes that support the growth of different bacteria. What scientists call the “A-type polymorphic form” (generated from cereal grains) forms double-helix shapes with a more compact, dry structure, while the “B-type polymorphic form” (generated from tubers with a high amylose content) forms a more open helix shape with higher water content. In studies, B-type forms result in higher butyrate production than A-type forms, suggesting that foods like cassava and cooked and cooled potatoes are better for increasing butyrate levels than grains are!
Sweet potatoes have also been studied for the gut microbiota-supporting properties.
In one study, consuming 300 grams daily of Benitenshi sweet potatoes (a Japanese cultivar with reddish-purple skin) for one week improved bowel condition, increased the ease of defecation, and caused no unfavorable changes in abdominal distention, while also significantly increasing levels of the operational taxonomic unit that contains Faecalibacterium species. Researchers have also tested polysaccharides extracted from purple sweet potatoes (including water-soluble polysaccharide [WSP], dilute alkali-soluble polysaccharide [DASP], and concentrated alkali-soluble polysaccharide [CASP]) on normal mice as well as those treated with the immunosuppressing drug cyclophosphamide. In normal mice, the water-soluble and concentrated alkali-soluble polysaccharides increased the levels of Bacteroidetes, Lachnospiraceae, and Oscillospira, while decreasing levels of Firmicutes, Alcaligenaceae, and Sutterella. In cyclophosphamide-treated mice, all three of the purple sweet potato polysaccharides increased the relative abundances of Bacteroidetes, Ruminococcaceae, Lachnospiraceae, Ruminococcus, and Oscillospira, while lowering the levels of Firmicutes, Proteobacteria, Alcaligenaceae, and Sutterella. All three polysaccharides also enhanced the production of acetic acid, propionic acid, and butyric acid in normal mice, while the water-soluble polysaccharide increased the production of these SCFAs among cyclophosphamide-treated mice. And in a study using an in-vitro fermentation system along with human fecal slurry, two different sweet potato varieties significantly increased levels of Bifidobacterium over the course of 24 hours.
In vitro, orange-fleshed sweet potato purees were shown to increase production of butyric acid when fermented by human fecal bacteria. Researchers have also tested polysaccharides extracted from purple sweet potatoes (including water-soluble polysaccharide [WSP], dilute alkali-soluble polysaccharide [DASP], and concentrated alkali-soluble polysaccharide [CASP]) on normal mice as well as those treated with the immunosuppressing drug cyclophosphamide. All three polysaccharides enhanced the production of acetic acid, propionic acid, and butyric acid in normal mice, while the water-soluble polysaccharide increased the production of these SCFAs among cyclophosphamide-treated mice.
Even the flavonoids in sweet potatoes can benefit the gut! In one study, anthocyanins from Chinese purple sweet potato increased the proliferation of Bifidobacterium adolescentis, Bifidobacterium infantis, and Lactobacillus acidophilus while also inhibiting the growth of Salmonella typhimurium and Staphylococcus aureus.
Across multiple studies, the ratio of Bacteroides to Firmicutes (two major bacteria phyla) has been correlated with obesity, with a higher ratio (more Bacteroidetes) associated with leanness, and a lower ratio (more Firmicutes) associated with higher body fat. In immunosuppressed mice, three purple sweet potato polysaccharides increased the relative abundances of Bacteroidetes while lowering the levels of Firmicutes, helping move the microbiota in the direction associated with leanness!
Like other starchy roots, cassava has proven prebiotic properties, making it a very gut-friendly food. A study of cassava bagasse (the fibrous, starchy components of cassava left over after the fresh root is processed) found that it could stimulate the growth of Bifidobacterium and Roseburia species, and in microbiota extracted from obese individuals, stimulated the growth of Bifidobacterium to a 10-fold greater degree than inulin did. In a study of oligosaccharides liberated from cassava pulp, levels of Lactobacillus gasseri (which has significant anti-inflammatory activity) and Bifidobacterium breve (which can potentially improve fat metabolism and skin health) increased dramatically, while also boosting populations of Lactobacillus reuteri (which produces vitamin B12 and folate), Lactobacillus acidophilus (which helps restore the microbiota after antibiotic treatment), and Bifidobacterium adolescentis (which reduces the mineral-binding effects of phytic acid) to varying degrees. In rats, feeding crackers comprised of cassava fiber and wheat flour (in ratios of 60:40 or 50:50) resulted in an increased Lactobacillus count, and in mice, xylooligosaccharides derived from cassava dregs (another byproduct of cassava starch processing) was likewise shown to promote the growth of Bifidobacterium and Lactobacillus species.
In rats, grain products supplemented with cassava fiber resulted in lower levels of Escherichia coli in the animals’ feces (while also 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 likewise shown to decrease the number of Escherichia coli present.
Yacón (a slightly sweet tuber native to the Andes) is rich in fructooligosaccharides (FOS), a highly fermentable carbohydrate known to support the grown of probiotic bacteria. (Some yacón crops contain up to 70% fructooligosaccharides on a dry-matter basis, so it’s no surprise this root veggie is an effective prebiotic!) Animal studies have also shown that a diet rich in yacón or yacón flour enhances the growth of bifidobacteria and lactobacilli. One rat study found that within one week of eating a diet containing 10% yacón root, the intestinal environment was significantly altered due to the abundant fermentation of yacón, leading to a significant increase in Lactobacillus acidophilus, Bifidobacterium pseudolongum, and Bifidobacterium animalis.
In rodents, diets supplemented with yacón or yacón flour have been shown to increase levels of SCFAs. Rats fed a diet containing 6% fructooligosaccharides and inulin from yacón (compared to a yacon-free control diet) experienced a beneficial modulation of the gut microbiome, including a significant increase in butyrate levels. Another rat study found that a week-long diet containing 10% yacon root led to SCFA production that was 70% greater than when fructooligosaccharides alone were used, suggesting non-FOS components of yacón were being fermented into SCFAs, too!
Yacón also contains natural antimicrobial substances, as evidenced by the fact that yacón crops require almost no pesticides to cultivate! Some of these substances have antibacterial activity against not only plant pathogens, but also ones known to infect humans, including Bacillus subtilis and Staphylococcus aureus. One mouse experiment even showed that yacón flour could prevent intestinal infection from Salmonella enterica serovar Typhimurium (S. Typhimurium), due to its ability to enhance non-specific immunity and improve the immunological intestinal barrier.
While not as extensively studies, there’s evidence of gut microbiome-boosting effects from several other root veggies. For example, inulin extracted from burdock root (a vegetable common in northern Asian cuisines, and which makes a great addition to stir fries, braises, and soups!) significantly boosted counts of lactobacilli and bifidobacteria in vitro. Jerusalem artichokes (no relation to actual artichokes!) are able to enhance levels of several Lactobacillus and Bifidobacterium species across a variety of animals, due to its high concentration of fructooligosaccharides (FOS).
And, turnip extract has been shown to inhibit a variety of potentially harmful microorganisms, including Candida albicans, Bacillus subtilis, and Pseudomonas aeruginosa, along with the stomach ulcer-causing bacteria H. pylori. The polyphenol apigenin, found in high levels in rutabaga, inhibits the growth of Klebsiella pneumoniae, Enterobacter cloacae, E. coli, Salmonella typhimurium, Proteus mirabilis, Enterobacter aerogens, and Vibrio harveyi.
Root Veggies for the Win!
So there we have it: in case we needed more reasons to add these delicious, versatile, and nutrient-packed veggies into our diet, we can do it for our gut!
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