Resistant Starch and Fiber in Potatoes

Back to my two favorite subjects: Potatoes and resistant starch. A new paper out, one that examined the fiber and starch profiles of numerous potato types. This is the first paper to fully describe the RS found in raw, cooked, and cooked and cooled potatoes.

Those weeds, they’re everywhere!

From the Food Chemistry journal, “Evaluation of nutritional profiles of starch and dry matter from early potato varieties and its estimated glycemic impact” (Pinhero et al, 2016). It’s still in draft, but I managed to sneak a few tidbits out for you.
Several studies reported that potatoes generally have medium to high GI, which has often adversely affected their consumption, but have overlooked the many nutritional and health benefits of potatoes.
Exactly as we have been saying here at the Vegetable Pharm since Day 1. Potatoes are good food. I’ve never payed much attention to the Glycemic Index (GI). If you eat real food, you have no worries. The GI is for those that eat at Burger King three days a week, and have donuts most days. Avoid processed food, and there is no more Glycemic Index to worry about. It has irked me to no end hearing potatoes compared to bags of sugar (Paleo Diet Roundup).
And just today, an article suggesting that “potatoes” are responsible for lung cancer!
The wrong carbs — white bread, potatoes, processed food — can lead to lung cancer.  People who eat a lot of these foods, according to a new study, had a 49% greater chance of developing lung cancer than those who ate a healthier diet…Even non-smokers are at grave risk.
I’d agree if this statement was qualified with “French fries and potato chips,” but the fact is, potatoes are one of the healthiest foods on Earth. Have you seen what’s going on in China? The Chinese government is promoting potatoes over rice because they’ve found potatoes to be a more complete food and it’s easier and cheaper to grow. Also potatoes do not require anywhere near the fertilizer and pesticide that rice does. The problem is, the Chinese seem to hate potatoes. But they are trying!
To the point, a new study examined the starch and fiber content in 14 types of potatoes when raw, cooked, and cooked and cooled. The potatoes used were standard varieties commonly found in the supermarket. To make things easier, I added the type they are in parenthesis and ranked them.
Have a read through the study if you are interested in the Glycemic Index or Glycemic Load, they went into a lot of effort to show that potatoes, when not in French fry and potato chip form are not such the high glycemic “bags of sugar” they have been portrayed as.
Ann Overhulse Photography

 

More to the point, these charts from
the paper:

Total Dietary Fiber:
There is no category for “uncooked” potato under Total Dietary Fiber because an uncooked potato is almost 100% TDF in all cases.

 

 

 


Resistant Starch Content:

 

 

 

 

 


 

Glycemic Index/Load:

 

 

Edited to add (3/15/16) :

 

I find these charts absolutely fascinating, it’s the best compilation I’ve ever seen in one place. And what’s
better, it confirms the RS contents that I found over the past couple years in diverse papers. 

Test Procedures
When making these charts, the researchers used the same potato for each test to eliminate errors. They took a raw potato of each variety and grated off some slices for testing “uncooked.” Then they boiled each potato for 10 minutes until tender and sliced off a couple more pieces. They immediately tested the hot potatoes as “cooked” and stored the cooled potatoes at 4 deg C (about 40F) for 48 hours for “retrograded”. I could not have designed a better test myself, this is perfect!
Results
1. There are big variances between potatoes in each category.
2. Raw potatoes have the most fiber and RS by a long ways.
3. Cooked potatoes drop very low in terms of fiber and RS. 
4. To get some fiber and RS back, cool your potatoes in the fridge, at least over night.
5. If you are concerned about Glycemic Index, cooling the potatoes lowers it 10-15%.
 
Take Home Messages
 
Potatoes are GOOD FOOD. Don’t let anybody fool ya. But don’t let anybody talk you into thinking that French fries and potato chips are anything like real potatoes. When I talk about potatoes, I’m talking about boiled, roasted, baked, steamed, or fried in a pan with minimal oil.  Not deep fried and soaked in artificial flavors and colors.
 

For best results, eat a VARIETY of potato types. Don’t just get the familiar looking ones, get them all from time-to-time. It’s fun to experiment with different types. There does not appear to be a pattern, i.e. reds have more fiber. They all just seem to be different. Keep in mind, though, they all have a great mixture of RS and fiber. No single potato could be called bad. The purple potato that measured very low in RS makes up for it in polyphenols and flavanoids from the purple pigments.

 
Don’t overlook raw potatoes. Don’t make them a meal, but when you are cutting up potatoes for dinner, have a slice or two raw. This will undoubtedly triple your fiber intake for the day. And also don’t overlook leftovers. In fact, make extra potatoes specifically for leftovers. This study did not test another hypothesis that re-heated and re-cooled potatoes grow in RS with each cycle, but you do not have to eat the leftovers cold (though you certainly can). Heat them up in the microwave or a pan with a bit of oil.
In some cases, if you look closely, you’ll see the RS actually decreased when certain types of potatoes were cooled. This is quite contrary to what I have believed was a hard rule. For instance, Carlingford, a white potato, was 3% RS when hot and 1.5% RS when cooled. Purple Fiesta went from almost 3% to nearly 0% when cooled. This just goes to show it’s never good to get too comfortable with how you fix foods. That same Purple Fiesta had 9% total fiber when cooked, and 13% when cooled, so it looks like a give and take. In other words…”It’s all good.” 
The Glycemic Index of all potato varieties dropped 5-10% when cooled as opposed to being eaten hot.
Thanks for reading, hope this was helpful.
Tim
Reference:
Pinhero, Reena Grittle, et al.
“Evaluation of nutritional profiles of starch and dry matter from early potato varieties and its estimated glycemic impact.” Food Chemistry 203 (2016): 356-366.
 

 

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  1. The Potato Hack » Penguin's Ponderings - September 30, 2016

    […] Cooling them does more than just keep them for later, too. The quantity of resistant starch changes based on cooling. I haven’t done a LOT of research on this, but some varieties increase in RS while others decrease. […]

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