Many places on the internet mention that chufa is rich in resistant starch. Good news you might say and we are only too happy to repeat it. Provided it is substantiated and that proved a bit trickier!

What is resistant starch?

Starch is a food reserve for plants. It consists of 2 parts, amylose and amylopectin. The ratio in chufa starch is¹:

11.5% amylose:

• is a polysaccharide
• Due to its complex structure, it cannot be broken down by the enzyme amylase found in saliva, among others
• is also too large in structure to be absorbed by the intestinal wall
• is not soluble in cold water but binds water as a thickener
• has a firmer structure than amylopectin and is therefore more resistant to digestion. The more amylose contains starch, the more resistant the starch is.

88.5% amylopectin:

• soluble in cold water
• smaller in size

For comparison, the ratio in other foods:

Corn starch 11.5% / 88.5%
Potato starch 26.5% / 73.5%

Resistant starch when heated

Amylose becomes water-soluble when heated. This means in practice, for example: you boil a potato to eat -> amylose changes its structure when heated and has become soluble rather than insoluble. On cooling, amylose partially regains its insoluble character (it retrogrades) -> a cooked cold potato with resistant starch is the result.

Why be happy with resistant starch

Resistant starch is a dietary fibre, it functions as a fermentable fibre with positive reactions in the intestines:

• resistant starch remains more or less intact on its journey through the digestive tract
• During its journey, it collects water that encourages regular bowel movements
• resistant starch promotes the development of healthy bacteria in the colon
• they can accommodate rapid blood sugar fluctuations just like soluble fibre
• resistant starch produces fatty acids in the intestines that help with weight loss. They stimulate the production of enzymes that shrink and activate fat cells.

Types of resistant starch

There are 4 types of resistant starch:

Natural resistant starch:
RS1: cell wall-enclosed and inaccessible starch in seeds, beans and wholemeal products, among others.
RS2: resistant starch granules; these are found in unripe bananas and raw potatoes. Ripening or cooking can make the starch accessible but also less resistant.

Non-natural resistant starch:
RS3: the already mentioned retrotreated starch. Occurs in processed products because it is created by heating or cooling, e.g. in cooled, cooked potatoes or pasta or cornflakes.
RS4 : resistant by chemical modification (comes from a factory)

Chufa is said to belong to the type 2 resistant starch. When heated, much of the resistant starch disappears. Eating it raw is therefore preferable. As for chufa flour, the amount of starch is the same so I assume also the content of resistant starch. When heated and cooled, RS2 changes to RS3. Studies have shown that the benefits of resistant starch are seen at an intake of 15 to 30 grams per day.

How much resistant starch does chufa contain?

This is where it gets tricky. Almost all websites mention that chufa is one of the best sources of resistant starch, but with no real substantiation. Except in a 2012 study (¹) describing the ratio of amylose to amylopectin. Chufa contains 23.7 grams of starch per 100 grams, which contains 2.73 grams of resistant starch according to that study. In comparison, cooled potatoes contain 4.3 grams of resistant starch per 100 grams of product. An amount of 100 grams of cooled potato is also easier to eat than 100 grams of chufa. However, it remains a nightshade and unripe bananas, raw plantain, raw potatoes or potato starch are also not really pleasant foods to consume for various reasons.

Based on this study, nothing wrong, however, our supplier also recently had the level of resistant starch in chufa examined. This showed a completely different figure:

It came up with a figure of 0.4%, which is 0.40 grams of resistant starch per 100 grams of chufa. That's not very much...

Then we came upon the following. The chufa is dried after harvest and in that process which takes a few months, some of the starch would be converted into sugars. Perhaps the chufa fresh from the ground contains more starch and therefore more resistant starch... a nice theory until we got clarity on that too. A fresh chufa contains 50% of moisture and 50% of dry matter. Of that dry matter, 50% is starch but so that also ends up being about 25% of starch on 100 grams of chufa. That's less rather than more than is in the dried chufa. It sounded so logical 🙂

The crazy thing is, when we make horchata (and we have heard this from several customers who have also experienced this), there really is a thick white insoluble layer sticking to the bottom...

After drinking the horchata, the bottle was filled with water. This has all the properties of resistant starch. It is not little and certainly more than 0.4%!

We prefer to write blog articles with a clear outcome but in the case of resistant starch in chufa (or tiger nut), ambiguity is the only clarity...

Anyway, in such cases, logic always wins out. The advice of 15 to 30 grams of resistant starch per day has been established by modern man. Since chufa is a major part of the diet of our distant ancestors mattered, couldn't it be that the chufa is good the way it is? The chufa is so-so a natural source of resistant starch no matter how much and so to eat. Our distant ancestors had fresh chufa but not cooled potatoes, rice, a dehydrator to make raw plantain chips or packets of Honig potato starch... they did, however, roam this earth for about a million years (we only 120,000 years).

So what is really the right amount of resistant starch to consume - perhaps much less than those 15 to 30 grams a day. Or our distant ancestors had less or no damage to the intestinal flora to repair so a little bit was enough...

Sources:
¹http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3364391/pdf/12249_2012_Article_9761.pdf
Wikipedia - https://en.wikipedia.org/wiki/Amylose
Wikipedia - https://nl.wikipedia.org/wiki/Zetmeel
– http://nourishedkitchen.com/tigernut-trail-mix-recipe/
– http://enjoyingthisjourney.com/the-low-down-on-tigernuts/
– http://www.mommypotamus.com/resistant-starch-cookie-dough-recipe/
– http://www.eurekalert.org/pub_releases/2013-04/fi-rsc042513.php