Carbohydrates have suffered a bad rap over the past couple of decades. We’ve been shunning bread, potatoes and pasta in the mistaken belief that these foods will cause us to gain weight. Yet much-maligned carbohydrates are a vital part of a healthy diet, serving as the body’s main fuel source and helping to protect against disease and weight gain.
The secret is the type of carbohydrates you eat. In some carbohydrates, the good parts have been stripped away in the interests of a longer shelf life and tastier texture (think pastries and cakes), while others are an important source of nutrients (think whole grains and legumes). And in the case of one special sort of carbohydrate that acts a lot like fibre, you’ll boost feelings of satiety (read: feel fuller for longer and perhaps even lose weight) and improve digestive health.
Different types of carbohydrates
Refined carbohydrates – mostly foods made with white flour, like white bread, pasta and biscuits – have been stripped of everything except the highly digestible parts, which causes the body to process them quickly in return for a sharp rise in blood sugar and energy. The downside is this process removes most of the nutrients.
At the healthier end of the spectrum, unrefined (or complex) carbohydrates like whole grains, fruits and vegetables are unprocessed and as such are broken down by the body at a slower rate. Evidence shows that eating plenty of these foods helps you control your weight.
Within these two types, carbohydrates come in a variety of forms. The most common are sugars, fibres and starches. The latter is the most common type found in our diet. Starch is digested and absorbed as glucose through the small intestine and used as short-term energy.
Up until recently, scientists believed that starch was always completely digested – just like other types of carbohydrates, regardless of the speed – but we now know that some starch resists digestion and offers a raft of health benefits.
The benefits of resistant starch
This type of carbohydrate is known as resistant starch. It’s thought to act in a similar way to soluble and insoluble fibre to help improve bowel health.
“Resistant starch is now considered a type of fibre,” says accredited practising dietitian Lisa Renn, spokesperson for the Dietitians Association of Australia and author of Body Warfare. “What this means is that it passes through the digestive system undigested, so it goes through to the large bowel where it’s broken down and fermented by bacteria.”
This process produces substances that help to keep the lining of the bowel healthy. And because resistant starch isn’t absorbed into the bloodstream or broken down into glucose, it doesn’t raise blood sugar and promotes sustained energy release. Plus, the slowed transit time of food through the digestive system extends the feeling of satisfaction, which aids weight control.
Cooked and cooled carbohydrate favourites are rich sources of resistant starch. “Pasta salad, rice salad and potato salad are all good sources of resistant starch because when you cool the starch it changes and becomes indigestible – whereas when it’s hot we can digest it,” says Renn. Resistant starch is also found in unprocessed cereals and grains, green bananas and lentils. It’s added to breads and cereals as Hi-maize.
However, Renn cautions against eating too much energy-dense pasta and potatoes. “Legumes are a good source of resistant starch as well as a fantastic source of protein, and they’re low GI. Whole grain foods are a good source of resistant starch as well as a good source of soluble fibre.”
The recommended intake of resistant starch is about 20 grams a day – equivalent to three cups of cooked lentils.
Using starch to battle bowel cancer
According to research by the CSIRO, resistant starch may help protect against bowel cancer – the second most commonly reported cancer in Australia.
“It is believed that resistant starch can lower the risk of bowel cancer by promoting normal epithelial cells in the colon and inhibiting the growth of cancerous ones,” says Dr David Topping. “Fibre is very good for regularity but resistant starch intakes may need to be increased to protect against cancer. Experimental evidence suggests that resistant starch can oppose damage to DNA caused by western diets which are high in energy-dense foods.”
Words by Angela Tufvesson