What are Sweet Potatoes?
Sweet potatoes, or Ipomoea batatas, originated in Central or South America and have been cultivated by humans for over 5000 years. Today, there are over 400 strains of sweet potato grown around the world. Different parts of the plant, such as the leaves, stems and root tubers, are used for food, medicine and animal feed .
Sweet potatoes are only distantly related to potatoes. Sweet potatoes belong to the same family as morning glory (Convolvulaceae), while potatoes are considered a type of nightshade (Solanaceae). Potato tubers are derived from the plant stems while sweet potato tubers are derived from the root .
Satsuma-imo, or Japanese sweet potato, is a sweet, yellow-fleshed strain. Traditionally grown in Japan and Okinawa, it is now available at grocery stores across North America. It is a staple food of the Okinawans, who are some of the healthiest and longest-lived people on Earth. Their good health and long lifespan are attributed, in part, to their diet [2, 3].
The Japanese sweet potato is distinct from the Okinawan sweet potato, which is purple-fleshed. The Okinawan people eat both in abundance .
Components in Japanese Sweet Potato Tubers
The phytonutrients associated with different colors in sweet potato do have different health properties. Besides that, however, sweet potato strains have a very similar nutritional profile. Rich in vitamins, minerals, and phytonutrients, sweet potato has been named the ‘healthiest of all vegetables’ by The Center for Science in the Public Interest .
Sweet potato leaves are rarely consumed in western countries but are a good source of fiber, protein, and minerals. The macronutrient, micronutrient, and phytonutrient information provided below are for the tuber, which is the part that’s usually eaten [1, 4].
In a 100 g (86 calorie) serving of sweet potato, there are 20.1 g of carbohydrates. Of this, around 12.7 g are starch, 4.2 g are sugars (sucrose, glucose, fructose, and maltose) and 3.0 g is fiber. Sweet potato starch is higher in amylose than amylopectin, which raises blood sugar slowly. This makes it a healthy food choice for diabetics .
Sweet potatoes are primarily a source of healthy starch and fiber, but they also contain 1.6 g of protein in a 100 g serving .
Sweet potatoes are very low in fat, with just 0.1 g in a 100 g serving. There are no saturated fats in sweet potatoes .
Sweet potatoes are a good source of many beneficial phytonutrients. While some phytonutrients are found in all sweet potatoes, others vary depending on the flesh color. The yellow-fleshed satsuma-imo is particularly rich in coumarins, peonidin, quercetin, kaempferol and chrysoeriol [7, 1].
Phytosterols are a cholesterol-like molecule found in plant cells. In a meta-analysis of 41 trials, consuming 2 g of phytosterols a day was found to lower low-density lipoprotein or LDL (‘bad’ cholesterol) by 10 % .
The most abundant phytosterol found in sweet potato is β-Sitosterol (55.2–77.6% of all phytosterols found). Campesterol was the second most abundant. Aliphatic alcohols and α-tocopherol were also found in smaller amounts .
Many polyphenols work as antioxidants in the human body. They help prevent heart disease, cancer, Parkinson’s disease and other neurodegenerative disorders .
Yellow-fleshed sweet potatoes like the Japanese sweet potato are rich in phenolic acids. They are especially rich in coumarins .
Health Effects of Japanese Sweet Potatoes
Japanese sweet potatoes can be a part of a healthy diet, which is essential to maintaining good health. However, neither Japanese sweet potato nor its extract has been proven to improve any medical condition. Talk to your doctor to develop strategies to address any health concerns you may have .
Insufficient Evidence For
The following purported benefits are only supported by limited, low-quality clinical studies. There is insufficient evidence to support the use of Japanese sweet potato for any of the below-listed uses. While Japanese sweet potato is considered safe to eat as food, it should never be used in place of something your doctor recommends or prescribes.
Sweet potato may help with constipation. In a study of 120 leukemia patients undergoing chemotherapy, eating 200 g of sweet potato per day prevented constipation and increased satisfaction with bowel movements .
In another study of 93 patients with heart disease (acute coronary syndrome), the group that received a treatment regimen including sweet potatoes, foot baths, and acupressure massage had significantly less constipation. They also used fewer laxatives and enemas and were more satisfied with their bowel movements .
Animal & Cell Research (Lacking Evidence)
No clinical evidence supports the use of Japanese sweet potato for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies listed below should not be interpreted as supportive of any health benefit.
2) Heart Disease
When mice were fed a high-fat, sweet potato diet for 16 weeks, their arteries hardened less than mice who were fed a high-fat diet without sweet potato. The authors suggested that sweet potatoes might help prevent the hardening of arteries caused by high-fat diets .
No human studies have yet investigated the effect of Japanese sweet potato on heart health.
3) Antimicrobial Activity
A protein (defensin) isolated from sweet potato tubers prevents the growth of fungi and bacteria. This indicates it may be able to fight microbes on contact, but much more research is required to determine whether it has any usefulness as an antifungal or antibiotic .
In an animal study, a carbohydrate (sweet potato polysaccharide) isolated from sweet potatoes was given to mice. At a dosage of 250 mg/kg, it stimulated the immune system function. This effect has not been studied in humans, so it’s unclear whether the effect would be similar and how much we would need to eat .
In a study of human cancer cells, polyphenols (caffeic acid and 3,4,5-tri-O-caffeoylquinic acid) extracted from sweet potato leaves suppressed cancer’s growth .
Another molecule isolated from sweet potato leaves, (Ipomoea batatas anticancer peptide, or IbACP) caused cell death in pancreatic cancer cells .
Note that these are extremely early results, and these studies do not suggest that eating sweet potatoes prevents cancer. They simply contain some compounds of interest to cancer researchers.
Limitations and Caveats
While there is ample research indicating that Japanese sweet potatoes are rich in antioxidants, there is very limited research on other health benefits. With the exception of one animal study that looked at the effect of sweet potatoes on artery hardening, all other research has been on sweet potato extracts. There is no evidence that eating Japanese sweet potatoes will have the same health benefits as concentrated extracts.
Sweet potatoes contain oxalic acid, which may combine with calcium in the kidneys to produce kidney stones in people who are susceptible. Many people around the world eat sweet potatoes as a staple food without any ill effects. But if you are on a low oxalate diet, you should talk to your doctor about what amount of sweet potato (if any) is safe to consume [1, 2].
Japanese Sweet Potato Recipes
If you are interested in trying (or already love) Japanese sweet potatoes, try this delicious low-lectin recipe! Japanese 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 Japanese 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!
Japanese Sweet Potato as Part of the Lectin Avoidance Diet
Japanese sweet potatoes, like all sweet potatoes, are low in 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 [19, 20, 21, 22].
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 .
Where can I get Japanese Sweet Potato?
Japanese sweet potatoes are available in the produce aisle of most grocery stores.
The Japanese sweet potato is a yellow-fleshed root vegetable rich in vitamins, minerals, and antioxidants. It can be incorporated into a healthy diet, which is one of the most important elements of a healthy life!
Early research suggests that Japanese sweet potato may have specific health benefits to the heart, digestion, and immunity, but more research is required. The clearest benefit may be to people who struggle with constipation.