Red and white skinned sweet potatoes
Image source: Bon Appetit
As I mentioned in Paleo Potatoes, part 3, Bovell-Benjamin reports that “Early records have indicated that the sweet potato is a staple food source for many indigenous populations in Central and South Americas, Ryukyu Island, Africa, the Caribbean, the Maori people, Hawaiians, and Papua New Guineans” (1)
Sweet potato has also served as a staple for several other groups with high immunity to diseases of civilization, including Kitavans and Okinawans. It appears that this tuberous root has some unique components that may help explain why these groups sustain good health.
Note: I don't intend this as a promotion of a high carbohydrate, sweet potato based diet, just an exploration of the properties of this tuber.
Sweet potato component combats diabetes
Japanese researchers have isolated from the skin of the white-skinned sweet potato a component, known as Caiapo, that appears to have insulin-sensitizing antidiabetic and possibly antiatherogenic properties. Studies with diabetic patients have had positive results.
For example, Ludvik et al compared 12 weeks of Caiapo supplementation at 4 g/d with a placebo in a randomized, double blinded study with 61 clinically stable type 2 diabetes patients treated with diet alone (2). Thirty patients received Caiapo, and 31 received a placebo. After 3 months, The following results emerged:
• Average fasting blood glucose declined 15.2 mg/dl, from 143.7 mg/dl to 128.5, in the Caiapo group, but decreased only 6.1 mg/dl, from 144.3 to 138.2, in the placebo group. After 3 months of treatment, 48.3% of patients in the Caiapo group had fasting blood glucose levels below 126 mg/dl, the level diagnostic for diabetes.
• Average HbA1c declined from 7.21% to 6.68 in the Caiapo group, but increased from 7.04% to 7.10 in the placebo group. Caiapo performed better than either acarbose or nateglinide in controlling HbA1c.
• Average total lipoproteins (“cholesterol”) declined from 225.1 mg/dl to 214.6 in the Caiapo group, but increased from 240.9 to 248.7 in the placebo group.
• Average triglycerides declined from 211.6 mg/dl to 205.4 in the Caiapo group, but increased from 216.1 to 219.7 in the placebo group.
• Body mass declined in both groups, but to a greater degree in the Caiapo group (Caiapo, 3.7 kg; placebo, 1.0 kg).
Ludvik performed another study, this one lasting 5 months. “This study confirms the beneficial effects of Caiapo on glucose and HbA1c control in patients with T2DM after 5 months follow-up. Improvement of insulin sensitivity was accompanied by increased levels of adiponectin and a decrease in fibrinogen. Thus, Caiapo can be considered as natural insulin sensitizer with potential antiatherogenic properties” (3).
Of course, this Caiapo intervention did not perform anywhere near as well as a low carbohydrate diet, as discussed by Stephan here. Nevertheless, it did a pretty good job in the context of a high carbohydrate diet; perhaps it would have had a greater effect if the participants had also restricted their total carbohydrate intake. In any case, it appears that the sweet potato has unique properties perhaps not had by other starchy foods.
Miyazaki et al showed that the anti-diabetic components of the white skinned sweet potato “increased phagocytic activity and phagosome-lysosome fusion in neutrophils and monocytes in a dose-dependent manner” (4).
Caiapo found in orange sweet potato flesh as well as skin
Although Caiapo comes from the skin of the white sweet potato, a team from North Carolina State University College of Agriculture and Life Sciences “discovered that the Beauregard variety of sweet potatoes - which makes up about 85 percent of the production in North Carolina - has essentially the same protein patterns as a commercial dietary supplement known as Caiapo, marketed to control blood glucose in diabetics….. [and] that the protein content of the flesh of the Beauregard sweet potato was higher than that of the peel” (5).
How I Apply Sweet Potatoes In My Diet
As I have pointed out, you can eat sweet potatoes in moderation and still maintain a pretty low carbohydrate diet. Presently, I only eat one on each of the days that I spend glycogen in resistance training. Even on those days I don't go above a total of 150 grams of carbohydrate.
1. Bovel-Benjamin AC. Sweet potato: a review of its past, present, and future role in human nutrition. Adv Food Nutr Res. 2007;52:1-59.
2. Ludvik B, Neuffer B, Pacini G. Efficacy of Ipomoea batatas (Caiapo) on Diabetes Control in Type 2 Diabetic Subjects Treated With Diet. Diabetes Care 27:436–440, 2004.
3. Ludvik B, Hanefeld M, Pacini G. Improved metabolic control by Ipomoea batatas (Caiapo) is associated with increased adiponectin and decreased fibrinogen levels in type 2 diabetic
subjects. Diabetes Obes Metab. 2008 Jul;10(7):586-92. Epub 2007 Jul 21.
4. Miyazaki Y, Kusano S, Doi H, Aki O. Effects on immune response of antidiabetic ingredients from white-skinned sweet potato (Ipomoea batatas L.). Nutrition. 2005 Mar;21(3):358-62.
5. Stanard S. Researchers reveal sweet potato as weapon against diabetes.