Purple sweet potato has sustained the Polynesian people for centuries, as it is rich in vitamins and minerals as well as fiber. Did you know scientists are researching its effects on diabetes, gout, and inflammation? Read on to find out the purported benefits of purple sweet potato and how to add it to your meals.
What is Purple Sweet Potato?
Traditional Use
Purple sweet potatoes (Ipomoea batatas Lam) are a direct relative of the well-known orange sweet potato and come from the same family. The difference in color is explained by the presence of anthocyanins and antioxidants that give the flesh its purple color [1].
The origin of purple sweet potato traces back to South America, but because it is such a robust farming crop, its production has spanned the world, including Africa and China. Over time, different types have been developed including the Okinawan, Japanese, Taiwanese, and Stokes varieties.
Nutrition
As a direct relative of the orange-fleshed variety, purple sweet potatoes are rich in essential vitamins (including vitamin A/beta carotene, which makes this crop even more important in commonly deficient areas in Africa) and minerals, as well as a large amount of fiber, which helps provide a sensation of fullness and satiety [2].
The abundant amounts of anthocyanins are unique to naturally purple-fleshed fruits and vegetables and provide many of the additional health benefits explored in this article [3].
The glycemic index (GI) of sweet potatoes varies based on the cooking method, with boiling providing the lowest score [4].
Boiling produces a GI of 40 to 50 while frying and baking raise the GI into the 70 to 80 range.
Although not commonly eaten, the leaves of purple sweet potatoes are rich in nutrients as well. Some of the antioxidants found in purple sweet potato leaf extract include polyphenols like the caffeoylquinic acid derivatives [5].
Remember to talk to your doctor before making any major changes to your diet and day-to-day routine.
Mechanism of Action
The anthocyanins of the root and the caffeoylquinic acid derivatives of the leaves are both active components of purple sweet potato.
Limited research suggests that anthocyanins may reduce blood uric acid levels (which in excess can cause gout) by [6]:
- Inhibiting an enzyme called xanthine oxidase, which produces uric acid from naturally occurring purines in the body [7].
- Decreasing transporters in the kidney that would reabsorb uric acid from the urine (GLUT9, URAT1) [8, 9].
Scientists consider that they might also reduce high blood sugar by increasing insulin sensitivity, decreasing inflammatory molecules, and increasing the production of glucose transporters in the muscle [10].
In animal studies, anthocyanins protected the liver by:
- Decreasing inflammation [11]
- Reducing tissue scarring [12]
- Inducing the production of the liver’s own antioxidant enzymes while scavenging free radicals on their own [13]
Researchers are investigating if caffeoylquinic acid derivatives reduce excess blood sugar by increasing the secretion of GLP-1, which stimulates insulin secretion while reducing glucose production in the liver [14].
These compounds might reduce oxidative stress and pro-inflammatory cytokine secretion after exercise, according to a small human study [15].
However, proper clinical trials are needed to confirm these effects and mechanisms in humans.
Purported Health Benefits of Purple Sweet Potato
A minority of the following purported benefits are only supported by limited, low-quality clinical studies. The remaining studies were performed in animals or cells. Such studies should not be interpreted as supportive of any health benefit.
Altogether, there is insufficient evidence to support the use of purple sweet potato for any of the below-listed uses.
1) May Support Cardiovascular Health
Limited evidence suggests that purple sweet potato may contribute to healthy blood pressure control.
In an open-label, non-comparative trial, 20 human volunteers with elevated BMI and blood pressure were given 2 cartons of a commercially-sold purple sweet potato beverage (with 117 mg of anthocyanins per serving) each day for 4 weeks. Systolic blood pressure dropped by an average of 10 points, from 140 to just under 130 over a 29-day period [16].
However, the study was done only in Caucasians, who were predominantly male. Additionally, they used an open-label study design, which opens room for bias and other issues. High-quality, randomized-controlled trials are needed.
2) Effects on Gout
Scientists are looking to see if purple sweet potato can reduce high uric acid levels that cause gout. Clinical trials are completely lacking, however.
In a study of rats with high blood uric acid levels, anthocyanin extract from purple sweet potatoes decreased blood uric acid levels by 30%. This was nearly the same level as the control group with normal uric acid levels [6].
3) Antioxidant Effects
The anthocyanins and polyphenols contained in the root and leaves might reduce oxidative stress in the body.
Anthocyanins can potentiate other antioxidants, and function as a free radical scavenger. In the lab, they increase the production of numerous antioxidant enzymes including [13]:
- Superoxide dismutase
- heme oxygenase-1
- NQO1 – NQO1 is a critical enzyme in breaking down toxic substances and cancer-causing substances
However, the clinical evidence is not as convincing. We found only one published human trial.
In 15 healthy males, stir-frying 200 g of purple sweet potato leaves reduced exercise-induced oxidative stress, including fat and protein breakdown into free radicals, compared to a control diet [15].
In the same study, increased polyphenols from the leaves were associated with a 63% decrease in oxidative substances [15].
More research is needed.
4) May Support Liver Health
Purple sweet potato is traditionally used to support liver health. The root’s anthocyanins may have liver-protective properties, but clinical trials are lacking.
In multiple rat studies, anthocyanin extracts reduced the formation of liver scar tissue and liver cell damage induced by a variety of toxic substances compared to rats who did not receive anthocyanins. This was demonstrated via the reduction of liver inflammatory markers in the blood (ALT and AST) [12, 11, 13, 17, 18].
Another rat study found that extracts from the Korean Shinzami strain of purple sweet potato prevented damage following “shock liver,” a condition in which the liver suffers great damage from a period of poor blood flow [19].
5) Blood Sugar Research
Both root and leaf extracts reduce excess blood sugar in experimental animals. No clinical trials have been carried out. Thus, this purported benefit remains unproven [20, 10].
In a study of mice with type 2 diabetes, adding 3% leaf extract to their food for five weeks led to reduced levels of blood sugar. In addition, it raised levels of GLP-1 (glucagon-like peptide-1), which helps suppress the rise of blood glucose [14].
6) May be Anti-Aging
Anthocyanin extracts from the root of purple sweet potato may be anti-aging due to their antioxidant properties. Clinical data are lacking, though.
In a study of mice, anthocyanin extracts showed a dose-dependent reduction of malondialdehyde, a free-radical and marker of oxidative stress, in addition to raising levels of antioxidant enzymes superoxide dismutase and glutathione peroxidase. It was comparable to the anti-aging effects of vitamin C [10].
7) Cancer Research
The root and leaf of purple sweet potato are being researched in animals for their potential anti-cancer properties. The current evidence does not support the use of purple sweet potato for cancer prevention due to a lack of data [21, 10].
In mice studies, purified protein from fresh purple sweet potatoes and the leaf extract were researched against colon cancer and prostate cancer, respectively [22, 23].
8) May Reduce Inflammation
Purple sweet potato root may have anti-inflammatory and immune-balancing properties. Human studies are needed.
In mice with leukemia, purple sweet potato root extract supplementation for 12 weeks restored immune cells (T cells, B cells, and T-helper cells), and decreased TNF-alpha production (a marker of inflammation). It also reduced liver and spleen swelling normally seen with the disease [24].
In the lab, freshly harvested sweet potato extracts inhibited the reactive oxygen species normally created from lipopolysaccharide, a key molecular component of some common infectious bacteria (endotoxins) that causes inflammation [25].
9) Galactosemia Research
Galactosemia is a disease often found in newborns, in which an enzyme deficiency causes the inability to break down galactose (a common sugar found in dairy foods). Eating galactose with this deficiency leads to liver failure, kidney failure, cataracts, seizures, and brain damage, among other issues.
No valid evidence supports the use of purple sweet potato for improving outcomes in people with galactosemia.
A study in mice with galactosemia found that purple sweet potato extract reduced liver cell death caused by the excess galactose. Scientists think its antioxidant properties may be important, as well as potential inhibition of cell death signals and enhancement of cell survival signals. Clinical trials are needed [26].
10) Weight Loss
In addition to reducing blood sugar and insulin spikes, purple sweet potatoes (both root and leaf) are high-fiber foods [5].
High dietary fiber provides the sensation of fullness and satiety, curbing urges to overeat. Purple sweet potato anthocyanins may also help with weight loss and body composition.
In mice and rats, purple sweet potato extract supplementation for 4 to 16 weeks reduced both total body weight and body fat after being fed a high-fat diet [27, 28].
11) Anti-Microbial Studies
Purple sweet potato root has antibacterial properties in cells. However, its effects on microorganisms in animals and humans are unknown.
In a bacterial growth plate study, purple sweet potato extract was plated with common infectious bacteria, including E. coli, Salmonella, Proteus, and Vibrio parahaemolyticus. The extract inhibited the growth of all of these bacteria [29].
Another study showed that extracts from the Sinjami strain had antibacterial activity against Staph aureus, Salmonella typhimurium, and E. coli [30].
No health-related conclusions can be drawn from these studies.
12) Potential Effects on Blood Clots
One of the caffeoylquinic acid derivatives (chlorogenic acid) may reduce blood clotting.
A study of blood samples in the lab explored chlorogenic acid effects and found [31]:
- A reduction in the activity of pro-clotting enzymes (activated factor X, activated factor XIII, thrombin)
- Reduction of fibrin clot formation
- Increase in time to clot formation (prothrombin time, partial thromboplastin time, thrombin time).
- Anti-clotting effects in mice
Additional studies are needed to determine the effects of purple sweet potato and its active compounds on blood clotting.
Limitations and Caveats
Many benefits of purple sweet potatoes were studied in animals and cells. While the findings are significant, these benefits may not apply to humans.
Long-term safety of anthocyanins and purple sweet potato extract has not been evaluated.
Using Purple Sweet Potatoes
Natural Sources/Forms of Supplementation
Purple sweet potatoes can be eaten as regular sweet potatoes and cooked in the same manner. Boiling provides the lowest glycemic index and likely maintains their nutritional content, but purple sweet potato can also be baked or fried. The leaves can be stir-fried [4].
The anthocyanin extract is available through many suppliers, though most are extracted from other anthocyanin-containing fruits such as blueberries. Extracts of purple sweet potato are available but more difficult to find.
Dosage
Dosing has not been established since many of the studies were done in animals. Clinical data are lacking.
However, in one study, the dosage of sweet potato drink (Ayamurasaki, sold commercially in Japan) for treating high blood pressure was 125 ml twice a day [16].
Drug Interactions
The drug interactions of purple sweet potato are unknown.
However, since purple sweet potato contains high amounts of potassium, people with heart conditions requiring a beta blocker should take caution and consume sweet potato in moderation. Beta blockers can cause elevations in blood potassium [32].
Similar caution should be exercised for those with kidney diseases [33].
Excessive levels of blood potassium can cause emergent heart problems.
Speak to your doctor before consuming large amounts of purple sweet potato to avoid any potentially dangerous drug interactions.
Side Effects
Purple sweet potato is not known to have any significant side effects when consumed as part of a healthy diet. The safety of its anthocyanin extract has not been established. Additionally, since sweet potato is rich in provitamin A, large amounts may result in orange tinting of the skin and body fluids [34].
User Experiences
“Really suppresses appetite. I’m not that hungry after eating even a small one ”
“I learned about these potatoes because my pup has a very sensitive digestive system and they helped her manage her loose bowels and upset tummy.”
“They are so delicious- especially with some babaganoush!”
“I microwave these potatoes and also eat the skin! I also bake them, keep in the refrigerator and eat one every day. I eat them warm or cold!”
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Do not consider user experiences as medical advice. Never delay or disregard seeking professional medical advice from your doctor or another qualified healthcare provider because of something you have read on SelfHacked. We understand that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified healthcare provider.
Mashed Purple Sweet Potatoes
This delicious dish is flexible and serves 4.
- Peel and cut 2 lbs sweet potatoes into large pieces, and place into salted water.
- Continue boiling until soft (easily pierced by a fork), and then drain.
- Add salt and pepper to taste, 3 tablespoons ghee, and 1/4 cup whole milk to drained sweet potatoes and mash until smooth.
- Season with desired herbs or toppings.
- Serve and enjoy!
