Thursday, September 17, 2009

Primal Potatoes, part 4

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
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.


Bryce said...

I wonder what, if any, similarities brown rice might have to sweet potatoes, as far as being a somewhat benign source of glycogen replenishment?

I've started having either brown rice or sweet potato the night before a heavy lift day. I tend to fast before I lift, so I guess I'm topping off the glycogen stores before I begin the fast. Thus, I go into the session with a reasonable glycogen supply, deplete most of it, and then go on for the rest of the week with a high level of insulin sensitivity.

Greg said...

I have been enjoying the primal potatoes posts. I would love to see a post on minimal carbohydrate consumption for maximum athletic performance without compromising health. Is the basic idea to not consume carbohydrates once your glycogen stores are full? I would think 150g of carbs would not fill up your glycogen stores.

Stephan Guyenet said...

Hi Don,

I think it's interesting to note that the sweet potatoes that are used as staples are typically less sweet than the ones we eat here (lower fructose content). Ours have been bred for sugar.

Sweet potato varieties that are eaten as staples such as the Caribbean batata are typically not sweet. The batata actually is similar to a potato in appearance and flavor-- starchy, white, dry and bland. I see it as "convergent evolution".

Don said...


I prefer sweet potatoes because they have a higher nutrient density and alkaline ash.


150 g carbohydrate will not fill glycogen stores fully. I would only want them full if planning to do a very exhaustive activity. For most recreational training, I would say that half-full stores will give all benefits--i.e. not more than 200 g.


Interesting. I haven't checked to see how much fructose a modern sweet potato contains...but I will guess that it is less than many fruits.

Jonathan Byron said...

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.

What about electrolytes? To me, that seems to be a key weakness of most low-carb diets (and one where potatoes, bananas, and other foods offer a key benefit). Potassium, Magnesium, and other elements needed for regulating osmolarity are found primarily in plant foods that are also high in carbs.

I know people that have to take a potassium supplement to prevent cramps when they eat low carb. This aspect does not seem natural or primal to me.

Don said...


You make a good point about potassium and low carb diets. I agree that they are weak on some micronutrients. I have not found a way to design a diet containing less than 75 g carbohydrate that also provides adequate magnesium and potassium. Hence, I don't recommend going below 75 mg carbohydrate. (see my Primal Diet on a Shoestring post).

When I tried going below 75 g carbs, or zero carbs, I got nocturnal spasms in my calves, which resolved when I reintroduced sufficient vegetables and fruits. Richest sources of magnesium are nuts, a low carbohydrate food.

However, I don't believe you must eat potatoes to get adequate potassium. Non-starchy vegetables and fruits also provide plentiful potassium. A medium potato provides 782 mg potassium. One-half of an avocado provides 680 mg, 1 medium tomato 440 mg, 100g raw kale 447 mg, 1 peach 308 mg, 1 cup strawberries 244 mg. Since most of these are lower in carbs and calories, you can consume large amounts of potassium without also ingesting large amounts of carbohydrates, if you eat liberal quantities of non-starchy vegetables and fruits.

On the other hand, I know from experience that people can lose fat while eating 100-200 g carbs daily and including bananas and sweet or white potatoes. I consider them primal foods since they appear in H-G diets.

Aaron said...

Don, any chance you could comment on this?

I don't always agree 100% with ray peat, but I have to say that what he is saying here is very intersting. Seems to poo-poo starches against fruit. Made me go back to this post:

Makes me think that the group with the highest AGEs were the ones with the highest polyunsaturated fat intake-- even though those stats were left out by the author of the study! Seems odd that the vegans had the lowest AGEs of the vegetarian groups-- I think this must be because they had the lowest polyunsaturated fat in the face of having the highest fructose intake!

Almost makes me rethink fructose a little- especially if you aren't consuming crap loads in one sitting!

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