What are resistant starches and why should you care?

Most of us were brought up on starchy carbohydrate foods: Potatoes, pasta, rice, and bread covered much of the plate, certainly at my home. If there wasn’t a starchy side, the meal seemed incomplete. Recently, however, starches have had a bad a lot of bad press. All starchy carbohydrates are broken down into sugar in the process of digestion. That way it isn’t just the sugar we eat that contributes to high blood sugar and insulin levels, but the starchy foods, too, even though they don’t even taste sweet.


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So, many of us now limit potatoes, rice, bread and pasta or have cut them out altogether. Not everyone has found it easy to let them go. But here’s some good news: We can bring some of them back, maybe slightly differently than we knew them, but we can, and that’s due to resistant starches.  

There are different types of carbohydrates: On the one hand there are sugars and complex, digestible starches, on the other there’s fibre. Yes, fibre is carbohydrate, too, but it is made up of cellulose rather than glucose, and our digestive enzymes cannot break up cellulose chains. Gut bacteria on the other hand can and happily do. Our friendly bacteria will ferment fibre and extract nutrients for us, such as vitamin K and B vitamins. They also create short-chain fatty acids, a type of fat not easily found in food, but they happen to be the most popular fuel for gut cells and are great for digestive health.

So where do resistant starches come in? These are made up of glucose – just like digestible starches – but for different reasons depending on the type of resistant starch, our carbohydrate-digesting enzyme amylase cannot get to them and is unable to break the starch down. So, while chemically, they are still starches, effectively they are fibre. Just like fibre, they feed beneficial bacteria, help increase microbial diversity (which is a good thing) and provide your gut cells with short-chain fatty acids.

Type 1 resistant starch (RS1) is contained in whole grains and pulses. It is surrounded by proteins and cellulose and as amylase cannot break through the cellulose, it can’t get to the starch either. The process of milling breaks down the cellulose barriers in grains, making the starches accessible. Overnight oats – soaked, not cooked – are a great source of resistant starch.

Type 2 resistant starches are resistant until cooked: You’ll find those in green bananas and raw potato starch. Once cooked, they become digestible.

The most popular type of resistant starch is probably RS3. This forms when our favourite – potatoes, rice, pasta – are cooked and then cooled. As those foods cool down, the structural shape of the starch molecules changes and therefore the enzyme doesn’t fit anymore. Enzymes work like a lock and key system. A type 3 resistant starch is a ‘warped key’. So, cook your starchy foods, cool them down quickly and pop them in the fridge as soon as they are cool enough. Leave them in there for 24-48 hours or even freeze. You can then use them in salads or even reheat them: Roasties and sautéed potatoes made from pre-cooked potatoes still contain resistant starches. The process is irreversible.  

So, there you are. You can eat healthily and still enjoy some of your favourites!