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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 it may be helpful in managing diabetes, gout, and inflammation? Read on to find out the benefits of purple sweet potato and how it can change your life.
What is Purple Sweet Potato?
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 [R].
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.
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 the sensation of fullness and satiety.
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.
The glycemic index (GI) of sweet potatoes varies based on the cooking method, with boiling providing the lowest score [R].
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 incredibly rich in nutrients as well. Some of the antioxidants found in purple sweet potato leaf extract include polyphenols like the caffeoylquinic acid derivatives [R].
Mechanism of Action
The anthocyanins of the root and the caffeoylquinic acid derivatives of the leaves are both active components of purple sweet potato.
Anthocyanins reduce blood uric acid levels (which in excess can cause gout) by [R]:
- Inhibiting an enzyme called xanthine oxidase, which produces uric acid from naturally occurring purines in the body [R].
- Decreasing transporters in the kidney that would reabsorb uric acid from the urine (GLUT9, URAT1) [R, R]
Anthocyanins also protect the liver by:
- Decreasing inflammation [R]
- Reducing tissue scarring [R]
- Inducing the production of the liver’s own antioxidant enzymes while scavenging free radicals on their own [R]
Health Benefits of Purple Sweet Potato
1) Purple Sweet Potato Helps Control Hypertension
Purple sweet potato can help you keep your blood pressure under 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 [R].
However, the study was done only in Caucasians, who were predominantly male.
2) Purple Sweet Potato May Treat Gout
Purple sweet potato can reduce high uric acid levels that cause gout.
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 [R].
3) Purple Sweet Potato Has Antioxidant Effects
The anthocyanins and polyphenols contained in the root and leaves reduce oxidative stress in the body.
Anthocyanins can potentiate other antioxidants, and function as a free radical scavenger. They increase the production of numerous antioxidant enzymes including:
- Superoxide dismutase
- heme oxygenase-1
- NQO1 – NQO1 is a critical enzyme in breaking down toxic substances and cancer-causing substances [R]
In 15 healthy males, stir-frying 200 g of purple sweet potato leaves reduced exercise-induced oxidative stress compared to a control diet, including fat and protein breakdown into free radicals [R].
Increased polyphenols from the leaves were associated with a 63% decrease in oxidative substances [R].
4) Purple Sweet Potato May Be Liver Protective
Purple sweet potato has a widely protective effect on the liver, largely through the root’s anthocyanins.
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) [R, R, R, R, R].
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 [R].
5) Purple Sweet Potato May Improve Diabetes
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 [R, R].
6) Purple Sweet Potato May Slow Aging
Anthocyanin extracts from the root of purple sweet potato may delay aging due to their antioxidant properties.
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 [R].
7) Purple Sweet Potato May Have Anti-Cancer Properties
In one mouse study, purified protein from fresh purple sweet potatoes reduced the growth and spread of human colon cancer cells introduced into mice [R].
8) Purple Sweet Potato May Be Anti-inflammatory
Purple sweet potato root has anti-inflammatory and immune-regulating properties.
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 [R, R].
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 cause significant inflammation [R].
9) Purple Sweet Potato May Protect Against Galactosemia
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.
A study in mice with galactosemia found that purple sweet potato extract reduced liver cell death caused by the excess galactose. This was achieved by its antioxidant properties, direct inhibition of cell death signals, and enhancement of cell survival signals [R].
10) Purple Sweet Potato May Aid in Weight Loss
In addition to reducing blood sugar and insulin spikes, purple sweet potato (both root and leaf) are high-fiber foods [R].
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.
11) Purple Sweet Potato May Be Anti-Microbial
Purple sweet potato root has antibacterial properties.
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 [R].
Another study showed that extracts from the Sinjami strain had antibacterial activity against Staph aureus, Salmonella typhimurium, and E. coli [R].
12) Purple Sweet Potato May Prevent Blood Clots
One of the caffeoylquinic acid derivatives (chlorogenic acid) may be helpful in preventing blood clots.
A study of blood samples in the lab explored chlorogenic acid effects and found [R]:
- 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
Purple Sweet Potato as Part of the Lectin Avoidance Diet
Purple sweet potatoes, like all sweet potatoes, are low in harmful lectins (to see a list of other foods low in lectins, click here).
Lectins are proteins that bind to carbohydrates. Although not all lectins are bad, some lectins and other substances found in plants can trigger immune reactions and damage the gut in certain people. These substances can be found in seemingly healthy foods like whole grains, beans, tomatoes, or fruit. Gluten (or gliadin), a protein found in wheat, barley, and rye, is a particularly dangerous type of lectin that can cause a lot of damage in the body [R, R, R, R].
Food sensitivity is a set of inflammatory or adverse reactions to food that isn’t an allergic reaction. While food allergies cause an immediate reaction (such as rashes, hives, pain, swelling, and in extreme cases, asthma/airway closure or anaphylactic shock), food sensitivities are usually not immediate and the inflammatory symptoms can last for a few days. Usually, a food sensitivity will cause symptoms that are obscure and don’t fit neatly into any diagnosis such as brain fog, pain, fatigue, anxiety, and insomnia [R].
Although there are food sensitivity tests available, several studies have shown they are not accurate or effective. The gold standard to identify non-allergic food sensitivities is to eliminate the food and bring it back. People with inflammation issues, autoimmune disease (Th1, Th2, Th17 dominance or leaky gut), histamine intolerance, or unexplainable health issues should experiment with an elimination diet, such as the Lectin Avoidance Diet, to see if their symptoms improve.
This cookbook is a guide to doing an elimination diet, starting with a list of foods that should be low in inflammation (usually doesn’t cause a reaction). After your symptoms subside, you can bring back eliminated food, one at a time, to see their effects. This cookbook allows you to figure out what works to reduce your symptoms, in a sustainable and delicious way.
Purple sweet potato is not known to have any significant side effects, nor the anthocyanin extract. However, since sweet potato is rich in vitamin A, large amounts may result in orange tinting of the skin and body fluids [R].
Limitations and Caveats
Many benefits of purple sweet potatoes were studied in animals and cells. While the findings are significant, these benefits may or may not apply to humans
Long-term safety of anthocyanins and purple sweet potato extract has not been evaluated.
No drug interactions have been well documented.
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 [R].
Similar caution should be exercised for those with kidney diseases [R].
Excessive levels of blood potassium can cause emergent heart problems.
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 maintains the beneficial effects, but purple sweet potato can also be baked or fried. The leaves can be stir-fried [R].
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.
Recommended dosing has not been fully established since many of the studies were done in animals.
“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!”
Purple Sweet Potato Recipes
If you are interested in trying (or already love) purple sweet potatoes, try this delicious low-lectin recipe! Purple sweet potatoes are flavorful, do not have any lectins, and are rated less inflammatory, which is great for those who have a lectin sensitivity. For a list of other foods low in lectins, click here.
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!
For more delicious recipes like these (such as Kale and Sweet Potato Salad, Korean Beef Lettuce Wraps, Coconut Hi-Maize Snickerdoodles, and many more), please check out our cookbook for a guide to doing an elimination diet and lectin sensitivity!
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