Reheating resistant starch

Reheating resistant starch is a very common question since banting began; thank goodness we can again enjoy potatoes, corn and pasta, but I do not particularly like them cold.

Really the word diet needs to be totally banished from our thinking; none of them work because they are not sustainable. However, giving up starches has worked for a lot of people, but can you abandon bread, potatoes, corn and pasta for ever, and is it actually necessary?

corn on the cob

This page was last updated by Bernard Preston on 11th March, 2021.

No, it is not and in fact it is not the right thing to do. Starchy foods like butternut, apples and beans, and whole grains, contain many of the vitamins and minerals, and phytochemicals that our bodies desperately need; we can avoid them in the short term for the greater good of losing 30 or more pounds, but for a long period it is not an advisable way to live.

Whole grains especially are strongly associated with greater well-being.

That is especially true if you then must turn to large amounts of animal fat and protein for energy; you will simply get cancer instead of developing cardiovascular disease.

The good news is that you can have your cake and eat it.

Well, that is an unfortunate metaphor in this instance; cake has zero resistant starch and it should be kept for high and holy days, and you cannot reheat it in any case. It will make you fat, and it will certainly downgrade your lifespan, whether it is the refined white flour or the sugar, it is total bad news; once a year on your birthday and perhaps a couple more times just so that you can deny that you have orthorhexia is fine, but for the most, avoid it.

Reheating resistant starch

Reheating resistant starch is for those on the Paleo and Banting meal plans for weight loss but really also for all those concerned about a healthy environment in the colon for their probiotics.

Firstly then, what is resistant starch?

Starches can be divided roughly into three groups:

  1. Rapidly digested starch; that in the main is your cake and colas, but also boiled, potato from cold storage, for example.
  2. Slowly digested starch; these would include legumes some of which are turned into glucose and absorbed in the small intestine but, because of the fibre, they are not at all like white bread and precooked rice.
  3. Resistant starch; these are carbohydrates that pass straight through the small intestine without being assimilated, reaching the colon where they act as prebiotics for the normal flora. Instead of being broken down into glucose, they are turned into wonderful short chain fatty acids; some call them indigestible since they get through the small intestine largely unaffected.

Often that means cooling your potato, corn cob, and pasta in the fridge overnight, a process called retrogradation, which is not such fun. But is reheating resistant starch an option? Yes, it certainly is.

Retrogradation of starches

It may be that this is a whole new subject to you, and there are all these impossible terms like reheating resistant starch and retrogradation of your carbs. Do not switch off. We were all there but, determined to enjoy being in fine fettle, we persevered and discovered to our surprise that in fact we could enjoy our pasta and potatoes again; and not get those unwanted blood-sugar surges and put on unwelcome pounds.

The starches in potatoes, corn and pasta normally are digested by enzymes in the small intestine and absorbed as glucose. In essence, that is quite normal but you would want to limit it so that you do not get a surge in blood sugar; ideally some of the amylose and amylopectin should reach the colon where they are greedily fed upon by the normal flora. Those are the bugs that scientists call the microbiome.

There they break down not into glucose but very important short-chain fatty acids for our immune systems.

When you boil a potato in water the two starchy constituents, amylose and amylopectin, lose their crystalline structure, absorbing water and form a gooey solution that the enzymes in the small intestine can devour and turn instantly into sugar; that is bad news if you have too much.

But if you first cool that potato before eating it, those molecules again form a crystalline structure with strong hydrogen-bonds bridging them, and making it very difficult for the enzymes in the small intestine to digest them; this is known in biochemistry as retrogradation. It is a very important word you should grasp if you want to lose weight permanently without all the pain of dieting.

But the problem of course is that we often do not like cold mashed potatoes, spaghetti bolognese and green peas; and corn on the cob. Is reheating resistant starch a possibility?

Yes, it is; scientists have found to their surprise that reheating your cold spuds and pasta actually lowers the expected surge in blood-sugar even more; you really can have your potato, and eat it.

Instead, your carbs, cooked and then cooled, and again reheated, pass through the small intestine into the colon as resistant starch where they are instead fermented by the healthy probiotic bacteria; instead of forming simple sugars with all the potential problems of obesity, diabetes and glucose intolerance, they are turned into healthy fats.

Yes, it is complicated but those who have an aversion to pills and pain will apply their minds to understanding the science; this simple vs complex carbohydrate page will give you another slant. Neither are good or bad; only different. 

Potato salad

Preparation time: 25 minutes, but they must overnight in the fridge once cooked.

Go for it:

1. Peel your spuds unless you are lucky enough to find new potatoes, and boil them until tender; better still pressure cook them for ten minutes.

2. Drain off the water and cool the potatoes; place them in the fridge, preferably overnight; this when retrogradation happens.

3. Chop the potato into smaller pieces, sprinkle with finely chopped spring onions and parsley, and drizzle with your cold pressed oil. Sprinkle with salt to taste.

4. As an alternative you could now place your cold potatoes into a hot oven for twenty minutes; turn once; even further retrogradation will occur.


  • One large potato per person, plus one extra.
  • Spring onions and parsley.
  • Any cold pressed oil; obviously from the olive is first prize, but vary it with macadamia oil perhaps.

I used to think that how to plant potatoes was only for the larger garden, but since it's so difficult to get new spuds, it's still best to grow your own; pop in a few chats as they are called between your flowers. The moles and wilt will also find it more difficult to locate them; in full sun remember.

So, you see, reheating resistant starch really is an option. The bugs in your colon will love it, and reward you with greater well-being and an improved immune system.


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How do potatoes help your immune system?

Well, this is complex immunology, but to put it as simply as possible, researchers have shown that a short-chain fatty acid called butyrate produced in the large bowel by fermentation of resistant starch that has passed safely through the small intestine, induces colonic T regulator (suppressor) cells[1].

They are crucial for tolerance of foreign proteins that would otherwise provoke an immune reaction; in short they would cause inflammation, both locally in the colon causing angry bowel disease and colorectal tumours, but also elsewhere in the body.

Thus white potatoes are included alongside refined rice, flour and pasta as pro-inflammatory foods that we should avoid or at least limit.

But boiled white spuds that have been cooled and reheated to form resistant starch are another whole ballgame; so too are new potatoes.

Frankly I cannot blame you for for being utterly confused; so was I until I started reading the research and trying to get my mind around why reheating resistant starch was an important subject.

Eat your potatoes, just not too many if they are hot and white, cool them when possible first and always choose red and new spuds given the option.

Beware of the neurosis known as orthorhexia; if you go out to dinner and your hostess offers you freshly boiled white potatoes, do not get huffy and puffy and give a lecture, but just ask for a small portion; add some butter. So says Bernard Preston, lover of life and good food.

One of the joys of cooking from scratch is that it gives back to you control of your well-being. For example, salt causing high blood pressure is not likely to be an issue.

We believe that by spending time on wellness you end up spending far fewer hours sitting in doctor' consulting rooms and at the pharmacy. So time spent planting old potatoes in your garden is certainly not wasted. Once you've tasted newly-harvested spuds you'll never go back to those from cold storage.

"Health nuts are going to feel stupid someday, lying in hospitals dying of nothing."

- Redd Foxx

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