Cooling pasta turns it into a resistant starch
Very interesting article from the BBC:
Many food-lovers worry about pasta making them fat. But could simply cooling and then reheating your meal make it better for you, asks Michael Mosley.
There are few things that really surprise me about nutrition, but one of the experiments from the latest series of Trust Me, I'm a Doctor really did produce quite unexpected results.
You are probably familiar with the idea that pasta is a form of carbohydrate and like all carbohydrates it gets broken down in your guts and then absorbed as simple sugars, which in turn makes your blood glucose soar.
In response to a surge in blood glucose our bodies produce a rush of the hormone insulin to get your blood glucose back down to normal as swiftly as possible, because persistently high levels of glucose in the blood are extremely unhealthy.
A rapid rise in blood glucose, followed by a rapid fall, can often make you feel hungry again quite soon after a meal. It's true of sugary sweets and cakes, but it's also true for things like pasta, potatoes, white rice and white bread. That's why dieticians emphasise the importance of eating foods that are rich in fibre, as these foods produce a much more gradual rise and fall in your blood sugars.
But what if you could change pasta or potatoes into a food that, to the body, acts much more like fibre? Well, it seems you can. Cooking pasta and then cooling it down changes the structure of the pasta, turning it into something that is called "resistant starch".
It's called "resistant starch" because once pasta, potatoes or any starchy food is cooked and cooled it becomes resistant to the normal enzymes in our gut that break carbohydrates down and releases glucose that then causes the familiar blood sugar surge.
So, according to scientist Dr Denise Robertson, from the University of Surrey, if you cook and cool pasta down then your body will treat it much more like fibre, creating a smaller glucose peak and helping feed the good bacteria that reside down in your gut. You will also absorb fewer calories, making this a win-win situation.
One obvious problem is that many people don't really like cold pasta. So what would happen if you took the cold pasta and warmed it up?
When we asked scientists this question they said that it would probably go back to its previous, non-resistant form, but no-one had actually done the experiment. So we thought we should.
Dr Chris van Tulleken roped in some volunteers to do the tests. The volunteers had to undergo three days of testing in all, spread out over several weeks. On each occasion they had to eat their pasta on an empty stomach.
The volunteers were randomised to eating either hot, cold or reheated pasta on different days.
On one day they got to eat the pasta, freshly cooked, nice and hot with a plain but delicious sauce of tomatoes and garlic.
On another day they had to eat it cold, with the same sauce, but after it had been chilled overnight.
And on a third day they got to eat the pasta with sauce after it had been chilled and then reheated.
On each of the days they also had to give blood samples every 15 minutes for two hours, to see what happened to their blood glucose as the pasta was slowly digested.
Dr Denise Robertson (back, left) and Dr Chris van Tulleken (back, second from right) with the volunteers
So what did happen?
Well we were fairly confident the cold pasta would be more resistant than the stuff that had been freshly cooked and we were right.
Just as expected, eating cold pasta led to a 50% smaller spike in blood glucose and insulin than eating freshly boiled pasta had.
“Our leftovers could be healthier for us than the original meal”
Dr Chris van Tulleken
But then we found something that we really didn't expect - cooking, cooling and then reheating the pasta had an even more dramatic effect. Or, to be precise, an even smaller effect on blood glucose
In fact, it reduced the rise in blood glucose by a further 50%.
This certainly suggests that reheating the pasta made it into an even more "resistant starch". It's an extraordinary result and one never measured before.
Denise is now going to continue her research - funded by Diabetes UK - looking at whether, even without other dietary modifications, adding resistant starch to the diet can improve some of the blood results associated with diabetes.
Chris was certainly blown away by this finding.
"We've made a brand new discovery on Trust Me I'm A Doctor", he says, "and it's something that could simply and easily improve health. We can convert a carb-loaded meal into a more healthy fibre-loaded one instead without changing a single ingredient, just the temperature. In other words our leftovers could be healthier for us than the original meal."
So heating and cooking your pasta two times could reduce the impact on blood glucose by 75% and effectively turn it into a fiber? Maybe miracles really do exist...
That's interesting because Dreamfield's used to claim that their magical pasta would lose its low-carb-ness if you overcooked it or reheated it. Of course now we know that it was never low carb to begin with.
This sounds too good to be true. If it weren't so frightening to run the risk of high BG, I'd try a little experiment with it myself. But not now.
I had read that about potatoes and rice, but not pasta. Very interesting.
I suspect there may be something different about bread though. Most bread is eaten cool. I wonder if it was chilled in the refrigerator (or frozen) is would be resistant.
I like Michael Mosley. Thanks for posting.
This is quite interesting. I read it to DH and he said, now I know why when I eat the reheated brown rice or pasta or potatoes, it doesn't bother me much! Pretty cool.
Not a real authentic trial in our house by any means, but if we stick to reasonable serving sizes AND reheat the food items, we seem to do OK. Who knew!
I wonder whether the test subjects had normal metabolisms? It may be that just slightly slowing down the rate of absorption means that a healthy body has more time to deal with the blood sugar, so the spike is not as large. It would be really interesting to run the test with people with diabetes, in case the reaction is different from healthy people.
How about toast?--
Would this mean that a slice of toasted bread would have less effect than plain white bread?
I don't think it applies to bread. I like reheated pasta and cold potatoes, so maybe this will enable me to have an occasional small portion.
This is very interesting and certainly easy to test if you have a glucometer. Of course, if you are wheat-free, it wouldn't make any difference.
I don't think bread would work as you'd likely need a food with naturally occuring resistant starch - example below:
Examples of naturally occurring resistant starch
Food Serving size Resistant starch (grams)
Banana flour,  from green bananas 1/4 cup, uncooked 10.5-13.2
Banana, raw, slightly green 1 medium, peeled 4.7
High amylose RS2 corn resistant starch 1 tablespoon (9.5 g) 4.5
Oats, rolled 1/4 cup, uncooked 4.4
Green peas, frozen 1 cup, cooked 4.0
White beans 1/2 cup, cooked 3.7
Lentils 1/2 cup cooked 2.5
Cold pasta 1 cup 1.9
Pearl barley 1/2 cup cooked 1.6
Cold potato 1/2" diameter 0.6 - 0.8
I may have spoken too soon on the bread issue. This article below makes mention of it as a possibility (toward the end). I also wonder how small a portion they were given, based on the waiter's comments. Anyway, I find this all very interesting!
Don't throw out cold pasta - 'resistant starch' could ward off diabetes
When starch in pasta is digested, it's turned into sugar very quickly
But cooking it then cooling it may increase its resistant starch content
By DR CHRISTOFFER VAN TULLEKEN
PUBLISHED: 22:26 GMT, 13 October 2014 | UPDATED: 13:11 GMT, 14
Cooking pasta then cooling it may increase its resistant starch content
Positano is an Italian restaurant in the middle of Guildford run by a gregarious family of Italian culinary geniuses: not an obvious setting for a science experiment.
Food, wine and a vast Italian family might otherwise undermine the sober accumulation of data.
Unless, that is, you want to film an experiment about pasta. Or, more specifically, why leftover pasta might be good for you.
That is what I was tasked with doing for the BBC, under the expert guidance of Dr Denise Robertson, a senior nutrition scientist from the University of Surrey. The subject of our experiment? Resistant starch.
It's hard to think of a less inspiring name for a food, so you can imagine my disappointment when the producers of the series Trust Me, I'm A Doctor said this was what I was going to investigate.
My co-presenters were flying to tropical locations, reporting on brain transplants and trying the latest aphrodisiacs, but I was off to Guildford to do an experiment about something that sounded only slightly more appealing than my other task for the programme: waxing my legs.
At least resistant starch wouldn't hurt, but I certainly had no expectation that it would change my eating habits.
I should also confess here that I'd never even heard of 'resistant starch' until then.
Like most people, I knew what starch was - it's what you get from foods such as bread and potatoes.
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But, as Denise explained, the difference between normal and resistant starch could be significant when it comes to their effect on your body.
When the normal starch in white bread and pasta is digested, it's turned into sugar almost as fast as if you drank the same amount of sugar in a sweet drink.
This is because normal starch is made up of tangled chains of glucose sugar molecules that are broken down into single sugar molecules extremely easily in your gut, and then quickly absorbed. If this sugar isn't burned off, it is turned into fat.
Normally, when starch in pasta is digested, it's turned into sugar very quickly
The other problem with this sudden rise in blood sugar is that it causes a spike in your insulin levels - insulin is the hormone that mops up the sugar in your blood.
That spike in itself is probably bad for you, even if you're not overweight, as over many years the body can become less sensitive to insulin, so it works less well.
The spike can also mean your blood sugar levels drop, so that you end up hungrier than if you hadn't eaten anything at all; you may have noticed this effect after a sugary mid-morning biscuit break. These then are the dreaded 'empty calories', which have little nutritional value and don't make you feel full.
This is why pasta, along with other white, starchy food, has taken a beating over the past few years. While some of the claims about the dangers are exaggerated, it is true that these foods do carry health risks and this is bad news for us Britons who won't think twice about double carbs for dinner: pizza and chips, beans and chips - a friend of mine even claims to enjoy 'potatoes and chips' (and she's a liver doctor).
Resistant starch occurs naturally in bananas (still a little green), some beans and pulses and raw oats
The difference with resistant starch is that some of those glucose chains are no longer broken down in your small intestine (where food is normally broken down and the nutrients absorbed).
This means that glucose goes into your blood more slowly, your insulin levels don't rise so high and you feel fuller for longer.
But that's not all. The undigested starch goes into your large intestine, where you have around a kilo of bacteria; the resistant starch acts like fibre, and is fermented by these bugs. It's then turned into chemicals called short-chain fatty acids, which are absorbed into your bloodstream and have a wide range of benefits, such as preventing heart disease and possibly lowering blood pressure.
One recent study showed that, in healthy volunteers, eating resistant starch could reduce some of the potentially harmful changes that eating red meat has on the gut.
Finally, of course, in acting like fibre, helps you poo.
As Denise explained all this about resistant starch, I started to wonder if, perhaps for the first time, I'd be able to use the word 'superfood' and mean it. This is where our restaurant experiment came in.
Resistant starch occurs naturally in lots of food such as bananas (but you've got to eat them while they're still a little green), in some beans and pulses, as well as raw oats. However, cooking starchy foods, then cooling them, may also increase their resistant starch content. That's what our experiment would test.
Cold pasta gave less of a spike in blood glucose
In general, when you see science on TV it's a case of doing 'demonstrations' of experiments that have been done before.
But in Trust Me, I'm A Doctor, we try to run new experiments.
It's extremely stressful and complicated, but although this is an age of television fakery, everything you see in this series is totally authentic.
The plan was this: with the restaurant staff as the subjects for our experiment, we would feed them pasta that had been pre-cooked. But half the group would eat it cold and the other would have it reheated.
We'd then test them over the next few hours to see how their blood sugar levels responded to these different preparations. The next day, the groups would be reversed. In order to do the experiment properly, each time they had to be starved for 12 hours first.
With the help of the head chef Ross (a bona-fide Italian, despite his name), we pre-cooked some imported dry penne and Ross covered it in a simple sauce of only tomatoes, garlic, salt and oil.
The reheated pasta was delicious, and bowls were emptied in seconds. But because of the experimental protocol, seconds were forbidden. This wasn't popular - one waiter claimed he would normally eat five times that amount for lunch.
We were fairly confident the cold pasta would be more resistant than the stuff that had been reheated. Just as expected, the cold pasta gave less of a spike in blood glucose and insulin than freshly boiled pasta would.
But then we found something very unexpected; the pasta that had been boiled, cooled and then reheated had an even more dramatic effect.
Reheating the pasta seemed to make it even more resistant. This means less insulin, less blood glucose, less hunger and more fibre.
You might think that ten people isn't many, but the result was so consistent that Denise is confident that it's robust science.
Cold pasta gave less of a spike in blood glucose and insulin... pasta that had been boiled, cooled and then reheated had an even more dramatic effect
She is going to continue her research - funded by Diabetes UK - which shows that, even without other dietary modifications, adding resistant starch to the diet can improve some of the blood results associated with diabetes.
Meanwhile after my initial scepticism, I've also become a real convert to the idea of resistant starch.
So how can you get this wonder-food into your diet?
Well, you can prepare pasta in this way, but it may be that freezing, then reheating many starchy foods could have the same effect - that is, freezing bread, pizza, and potatoes, then reheating them after cooking and cooling, may all increase their resistant starch content.
Cooled roast potatoes are also a good source. (In the U.S. you can buy flours such as Hi-Maize that are produced specifically to have a high resistant starch content, but they're not available here.)
Resistant starch isn't going to end the age of obesity, but it looks like it will be a weapon in the arsenal. For most of us, to prevent weight gain or to lose weight we'll need to make a huge number of small changes, and this - eating heated-up leftovers - could be one of them.
We need more research into resistant starch done by scientists such as Denise Robertson, but she's going to need to get in touch with some PR people for a name change if it's going to take off.
Dr van Tulleken is an infectious disease specialist at University College London. His research is funded by the Medical Research Council. Trust Me, I'm A Doctor is on BBC 2 tomorrow at 8pm.
This is very exciting. I would really like to know what a nutritional analysis of these foods are at various times during the process, but the way these things work it could be years before we have any more info on it. It's got me considering getting a blood sugar testing kit so I can see what the effects are. Who wants to have to wait 3 years for potato salad and real pasta? I am a bit worried that although cooling/reheating seems to lower the number of used carbs, it still won't be low enough to help with weight loss.
The point of resistant starch isn't *just* to lower the carbs. When starch is resistant is feeds your good gut bacteria, and the more healthy your gut is, the better off you are. Some people believe a healthy gut is the difference between being thin and being overweight and a myriad of other issues.
I'm really liking the new sweeteners that help beneficial bacteria as well. They're more natural, they're probiotic, and they taste great and cook up a lot more like real sugar. If this new starch research works out, then to my mind, the only nut left to crack will be coming up with better flour replacements that act more like the real thing. It would be SO nice to be able to make food that tastes the way my memory says it ought to.
I'm remaining skeptical for now though, since one of my old favorite cooked and cooled starches is potato chips, and oddly, it didn't seem to lower their carbs enough to make them acceptable for losing weight, and if they produced any beneficial bacteria, it never made me skinny :-)
I've read about RS in quite a few different sources (reliable or not I can't really say), and they always talk about "chilling" the starchy food, not just cooling it. There is also a time at a chilled temp requirement. I forget the specifics, but I remember the refrigerator overnight is supposed to do it.
Wheat doesn't have the right kind of starch as I understand it, and chips are not typically refrigerated.
I'm sure I just lost at least part of a pound laughing. :laugh:
Remember the old fake diet fad? Nothing has calories if you eat it with a diet coke? We could start a new one now - nothing has carbs if you freeze it. Then we market our new line of potato chip popsicles...
That's interesting about the cooling vs chilling. I am curious enough that I've ordered a glucose testing kit, and I'm going to add that to my tests. I'm thinking of doing a baseline first, and then testing with 1/2c cooked hot new potato, then cooked cooled, and now adding cooked chilled (and possibly cooked frozen). I'll get those numbers and then repeat each of those with a re-heat after. Obviously, this will take a while, but I've already invested way more time than that experimenting with potato substitutes and making low-carb pasta, and I'll get to eat a potato, so yay for that. I'm currently stalled anyway, so I may as well check this out before I go for another induction round.
Re. the flour..yeah, I didn't expect that to fall into the same RS category. I'm just wishing for a breakthrough in that the same way we've just gotten one with the sugar subs and now possibly with the starches.
[QUOTE= Then we market our new line of potato chip popsicles....[/QUOTE]
You are both cracking me up!
Clues, I like your humorous and investigative spirit. Love to hear how your glucose testing goes with this! Ps: I agree about flour replacement but I've learned to make baked goods where no one it isn't flour - it is possible :)
GME - interesting about the cooling vs chilling...
I am wondering how popcorn would work. Pop the corn, freeze it, then reheat it in the oven. :)
Can't wait for our peeps to do the test. I have a glucometer so I could try it sometime.
I would use Dreamfields cuz that is what I have.
I am by no means an expert, but I don't think corn has RS. If it does corn tortillas would be perfect. I keep them in the refrigerator anyway.
I use Dreamfields and have had no blood sugar issues as long as I don't go over 1 cup at a time. Regular pasta would send me to about 180 at a 1 cup portion. I am anxious to know how the reheating would work with Dreamfields. I am not able to check my own blood sugar (hubby has to do it) so I cannot do the experiment until he is here around Christmas time.
I want a glucose meter now.
I'm such a dork about stuff like that. I take my pulse and blood pressure all the time and sometimes monitor my sleep.
This is interesting. I have been experimenting w the glucometer, seeing exactly which carbs spike by blood sugar and by how much. I was surprised last week when some cold red potatoes barely made a dent-- I had roasted them for my husband the night before. I didn't reheat them, but ate them cold. IIRC my blood sugar was in the 80s after which I usually obtain only after a low carb meal. I did eat them very slowly though which also probably kept the level down.
There is a product called Hi-Maize Resistant Corn Starch and Netrition sells a resistant corn starch also - I bought it because I found a cookie recipe that called for it, but didn't find it added much to the cookie. Plus, I believe it is a GMO product so I doubt I'll use it again.
There are long threads in the JUDDD section about the "potato hack" diet, where you eat cold potatoes - please forgive me for being so vague but I haven't read the threads or tried the hack, but might find some time to read them now - the conversations might anecdotally support the info in this thread.
I had forgotten about the resistant corn starches. Maybe tortillas would work the same way.
I typically only eat organic corn products to avoid GMOs.
I read a bit more about resistant starch and it seems bread develops some resistant starch after freezing, thawing and toasting, which is what I do anyway.
I use the Bob's Red Mill RS most mornings with a bit of milk and my BS was better than usual the last lab work I had in May. I am prediabetic so I watch pretty close. As with most food the key to not gaining is portion control.
Are you using the Bob's potato starch Heidienem?
subbing so I can keep up with all your experiments with RS. If it works for you, here comes some potato salad for me! love it!
My glucose testing kit is due to arrive today. I'll spend a few days getting baselines, and hope to be testing next week!
***Warning. Boring Numbers Follow***
I've been thinking about how to use the information I get from this. The British doctors said that cooling the item reduced the sugar spike by 50%, then reheating reduced it another 50%. Let's say I see the same thing in my testing.
I don't know how to turn this into a carb count other than subtracting 50% of the original carbs, and then a further 50% of that for the reheating. I don't think this will actually be the correct number though. It would probably take a food testing lab to figure the actual nutritional value of the cooked/cooled and cooked/cooled/reheated item.
Just as an example:
1/2C. diced red potato - 12 carbs, 1.3 fiber - 10.7 net carbs
cooked and cooled (-50%) - 5.35 net carbs
cooked, cooled, reheated - 2.67 net carbs
So these numbers subtract 50% of the net carbs each time. It is probably a lot more complicated than this because not only are the carbs being reduced, the fiber is being raised. Using those kinds of numbers gives a different result:
original - 12 carbs, 1.3 fiber
cooked/cooled (reduce each by 25%) 9 carbs and 1.6 fiber - 7.4 net
c/c/r - 6.75 carbs and 2 fiber - 4.75 net
I wish there was some lab we could get to do the test and provide the nutritional analysis. If the blood sugar spikes show the same results as the British doctors found, then all we may be able to conclude from it is that the CCR method may be able to produce starches we can include in a low carb diet. This makes me happy because....starch(!), CCR (Creedence Clearwater Revival)... :-)
But I'd rather have a nutritional label for it.
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