When you want to have some potatoes with your dinner, do something a little different. Cook them the day before (ideally steam or roast them), then allow them to cool overnight in the fridge before reheating them the next day.
It sounds strange, but something magical happens to potatoes when you cook and cool them in this way. Their fibre intake goes up considerably. But it’s not the ‘roughage’ that we associate with fibrous plant foods, it’s a type of fibre called resistant starch that has some powerful health benefits.
Now this is good news, because any way you can increase your fibre intake will benefit you, as most people in Australia simply don’t eat enough fibre. The recommended intake is 25 to 30 grams per day. The average intake is about 20 grams a day. Compare that to our Paleolithic ancestors whose fibre intake is estimated at 90 to 100 grams per day.
What is starch?
Starches are long chains of glucose molecules that are found in grains like rice, in legumes, potatoes and various other foods. Most starch is easily digested. It is dissolved in the small intestine and then absorbed by your body, providing you with glucose and other nutrients. This is why your blood glucose, or blood sugar, increases after eating a starchy food.
But not all the starch we eat gets digested, and sometimes a small part of it passes through the digestive tract unchanged – that is, it is resistant to digestion.
You can find resistant starch in a number of different foods, as there are different types. Grains, seeds and legumes, raw potato and green (unripe) bananas. But a type of resistant starch is also formed when certain starchy foods, including potatoes, pasta and rice, are cooked and then cooled. The cooling turns some of the digestible starches into resistant starches via a process called retrogradation.
Why is resistant starch so good for us?
One of the main reasons why resistant starch improves health is that it feeds the friendly bacteria in the large intestines. There is a particular species of bacteria in your gut that specialise in breaking down resistant starch, a process that provides the bacteria with the fuel they need to survive. The bacteria use the starch for energy, during which they release small carbohydrate molecules that serve as food for different neighbouring bacteria.
As these bacteria continue to feed, they excrete even smaller molecules as waste, and one of the final waste products is a short-chain fatty acid called butyrate, an energy source for your body.
More about butyrate
Butyrate encourages blood to flow into the vessels of the large intestine, keeping the tissue healthy. If your diet includes enough resistant starch, these cells will use butyrate as their main source of energy. In fact, it’s believed that butyrate has been around our guts for so long that the lining of our large intestine has evolved to use it as its primary source of energy.
Butyrate can protect you from cancer, particularly bowel cancer. In Australia, bowel cancer (or colorectal cancer) is the second leading cause of cancer death, and 17,000 new cases are diagnosed every year.
Intestinal cells are sensitive to DNA damage, caused by environmental factors. If a cell’s DNA is damaged, a mutation can occur. As the cell divides, more damage can accumulate which can lead to colorectal cancer. But a steady supply of butyrate allows the damaged cell to be more easily detected and killed off. Good news for you, as it can’t progress to form a cancer.
Other benefits of resistant starch
- Resistant starch can improve insulin sensitivity, meaning that your body responds better to the hormone insulin. This means that you’ll lower your blood sugar levels, along with your risk of type 2 diabetes, obesity, cardiovascular disease and Alzheimer’s Disease. Some studies have found a 33-50 per cent improvement in insulin sensitivity after only four weeks of consuming more resistant starch.
- Resistant starch can improve a number of different digestive disorders, including inflammatory bowel diseases like ulcerative colitis and Crohn’s disease, constipation, diverticulitis, and diarrhoea.
- Adding resistant starch to food increases the feelings of fullness and makes people eat less, so it can help you lose weight.
Where else can you find resistant starch?
Apart from cooked, cooled potatoes, other sources of resistant starch are cooked, cooled rice and pasta, cashew nuts, green bananas, uncooked rolled oats, white beans (canned or cooked) and lentils.
And in case you’re worried about possible bloating and flatulence as side effects of eating resistant starch, rest assured your large intestine and gut bacteria gradually adapt to an increased intake, and symptoms usually decrease.