In medieval Europe and going all the way back to Classical times, alchemists were attempting to turn one element into another, for instance, a “base” metal like lead, into a “pure” one like gold. Well, as far as we know, they never succeeded but the idea isn’t so far-fetched when you consider that in your own kitchen, you have at your disposal the raw materials to perform some nutritional alchemy. We call it “resistant starch.” 

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As all my readers probably know by now, I’m not a big fan of consuming random loads of carbohydrate. The crux of the problem is that when we eat low-fiber, high-carb foods, they readily turn into glucose, e.g. sugar, which floods into the bloodstream, raising insulin levels and setting the stage for our sky-high obesity, pre-diabetes and type 2 diabetes rates. 

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However, starchy foods like rice, potato and pasta all contain some amount of ‘resistant starch’ which, true to its name, resists being broken down into glucose and passes intact to the colon. There, that resistant starch acts as a prebiotic, feeding our good gut bacteria. Here’s where the alchemical switcheroo works its magic: If, after we cook these starchy foods, we cool them down in the fridge for a night, we actually increase the amount of available resistant starch – think pasta salad or potato salad. And, while I’m certainly not advocating overdoing carbs, this neat twist of body chemistry is good news, allowing those of us who enjoy starchy foods to eat them in moderation, and to take advantage of their health benefits, which can include lowering insulin levels, and tamping down appetite – and helping to support gut heath. 

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Interestingly though, this isn’t even the whole story. In fact, when you dig into higher fiber carb-rich foods, for instance legumes like lima and butter beans, and whole grains like barley, turns out, they don’t depend on the cook-and-cool method and, on the whole, they deliver even bigger resistant starch health boosts. In other words, there’s a lot to like here! So, how to tap into all the benefits resistant starch’s (RS) got to offer? How to make a new nutritional friend out of what for years a lot of people used to think of as a starchy old foe? Here’s where to start:

Food chemistry 101.

OK, so, from the top...Starches are long chains of glucose (sugar) molecules which most of the time get broken down to their basic glucose form inside the small intestine. But, as we discussed, within those starchy foods, a portion of the starch is RS, the stuff that resists the back-to-glucose process. 

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Take the green banana, an RS winner. But leave it out for a few days and it produces a ripening hormone which activates a bunch of starch-degrading enzymes. Basically, Mother Nature is doing the same thing to the banana that your small intestine does, breaking down those chains of starch into sugar and reducing the amount of resistant starch. That means when you eat that yellow (or worse, turning brown) banana, it digests quickly, easily, and raises your blood sugar. 

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On the other hand, when we’re talking rice or pasta or potatoes, the transformation works in reverse, in our favor, this time, with a little help from us. First up, these foods need to be cooked to be eaten. That cooking process causes the starch granules to swell, making them considerably more edible, and easier to digest (too easy!). However, give these foods a full night in the fridge and those starch molecules reorganize into tighter structures, a process called retrogradation – and voila! your cold rice or pasta or potato salad has more resistant starch. Pretty cool, eh? 

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It is, however, important to keep in mind that the amount of RS, and the health benefit, depends on the type of food -- the differences between similar looking foods is considerable. For example, cooking and chilling a 3 ½ ounce portion of russet potatoes will net an impressive RS load of 4.3 grams. Do the same with red potatoes though, and you’re looking at roughly 2 grams, not quite in the same league. 

The “Resistant” cookbook.

This is one book that’s a pretty short read. Cook the starchy food, chill it thoroughly – overnight is fine – and next day, you’re good to go. You can even gently reheat the dish in the morning and you won’t lose much or any of the resistant starch bonus. (Good news for all you meal preppers out there too.) Better yet, you don’t have to eat everything cold to harness the benefits. So, here’s what to do with a few of your faves:

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• Bread:  Freeze first and then toast, straight out of the freezer. Turns out freezing and toasting both raise resistant starch. Together, they have an additive effect. And this cold-hot treatment doesn’t harm the texture of the bread at all. 
• Pasta: Same drill, cook and refrigerate. Here, cold pasta salad is the obvious choice, not to mention a great vehicle for loading on the healthful veggies. Pro chef bonus: cooking the pasta al dente also ups the resistance. 
• Potatoes: Boil or bake and then pop ‘em into the fridge for the night. Pretty much everyone who loves potatoes loves cold potato salad. Make it russet potatoes and you got a star RS dish. Rewarming the spuds for something other than a salad still beats potatoes straight out of the oven. 
• Rice: Cook and then get in the fridge quickly, for at least 12 hours. Chilled rice gets a big resistant starch bump up. 

Resisting digestion, promoting gut health.

Resistant starch behaves in the human system very much like soluble fiber. That is, it serves as a prebiotic that feeds the good bacteria in the microbiome. That’s a story worth re-telling. When these gut bacteria ferment the starch, they produce as byproducts a number of short-chain fatty acid compounds, the most significant of which is butyrate. 

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These compounds help support and repair the lining of the colon, preventing bacteria and tiny bits of undigested food from escaping into the blood stream where they can trigger systemic inflammation – anything from skin rashes to brain fog. As well, a topped-up microbiome increases the number and diversity of bacterial species, so it can do a better job helping to prevent the gut immune system from overreacting to non-toxic compounds that enter the GI system, and help produce the vitamins and neurochemicals that keep our entire systems running smoothy. 

The right starch (means a healthy metabolism).

A number of studies have looked at the metabolic benefits of consuming resistant starch. Mind you, the research subjects aren’t generally eating a lot of green bananas. They’re being dosed with a resistant starch supplement, a form of corn starch (related to but not the same as the stuff that you buy at the supermarket to thicken a sauce) that is high in a particular form of RS, amylose, that’s highly resistant to our digestive enzymes.

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 A 2019 metanalysis, an analysis of 13 RS studies, found that an RS protocol resulted in improved glucose and insulin levels and improved insulin sensitivity, especially for overweight people with diabetes. In other words, when much of the starch you consume goes to your colon instead of being converted to sugar in the small intestine, good things happen. Other studies have looked at RS’s ability to help moderate glucose and insulin spikes after a meal. Even more eye-opening is a research literature that’s found a “second-meal effect.” That means the metabolic benefit you get from consuming a hearty amount of RS at one meal carries over to your next, even if you don’t eat any more RS. The boost you give your microbiome at the first meal turns out to have an impressively long shelf life! 

Intriguing possibilities on the starch frontier.

Other possible RS health benefits are intriguing even if they haven’t yet been completely pinned down. We have preliminary evidence that eating RS may help shrink appetite. For example, one clinical trial of 20 healthy young men found that consuming the corn starch supplement reduced the number of calories they ate over the course of a day. A team of German researchers put their 12 subjects on a month-long RS diet and analyzed its effect on the colon function. They speculated that resistant starch could someday emerge as a complementary therapy to protect against colon cancer, welcome news given the rising rates of colon cancer that we’re seeing now in young people.        

Looking at the RS big picture.

One team of researchers actually estimated the amount of RS we get in the American diet – about 4 grams for a daily 2,000-calorie diet – and suggested we’d all be better off with 15 grams a day. Maybe so. But that doesn’t mean a free pass to eat unlimited amounts of potato salad. Really, the RS story folds into the larger fiber story. Most of us simply don’t eat enough fiber. And, when we load up on nuts, seeds and – and moderate amounts of legumes and whole grains (if you can handle them) – we’re getting our resistant starch and a healthful haul of fiber. That’s what makes a body happy.