What is starch?
Starch is a complex carbohydrate and is the storage form of energy for plants. Starch is common in plant foods including cereals, root vegetables and tubers, beans, and peas. As such, starchy foods that appear most commonly in our diets would be rice, pasta, bread and starchy vegetables like potato and sweet potato.
Now, a wee bit of starch science is necessary here… Nothing to scary, so stay with us. Different food sources will contain starches in differing structures and as such, they will be digested differently. Amylose and amylopectin are the two major polysaccharides that make up a starch molecule. Amylose is a long, mainly unbranched chain of glucose units, which we digest slowly. Amylopectin is highly branched, and is broken down more quickly therefore creating a rise in blood glucose and insulin levels. Starch molecules are usually made up of more amylopectin than amylose.
So, are there good and bad starches?
Kind of… Starches are processed differently depending on their use and while starches do pack a punch in terms of carbohydrate content, they also contain important vitamins, minerals, and contribute to our intake of all-important dietary fibre. Legumes for example, contain high levels of starch but are also an important plant-based protein that contains vital nutrients and contributes to the feeling of satiety (fullness).
To really understand the effect starches have on our body, we need to look at refined starches and resistant starches.
Refined starches are grains that have had their super nutritious husk removed, and as such have lost much of their health promoting properties. White rice is a good example of a refined starch, whereas brown rice is non-refined as it still has the outer husk intact. As a result, brown rice is higher in dietary fibre and also higher in amylose. Remember that amylose is broken down more slowly and helps keep us fuller for longer without inducing an insulin spike like simple carbs do.
Refined starch is super common in the typical Western diet and features strongly in processed foods, particularly products made from white wheat flour. We’re talking breads, pasta, pizza, and baked goods. These are the starches we want to avoid! They often accompany high amounts of fat and sugar in processed foods, are cheap and convenient, and as a result are contributing to the global increase in overweight and obesity. When the cancer prevention guidelines are telling us to limit starches, they’re mainly talking about refined starches. High body fat is a risk factor for several cancers, as well as metabolic disorder.
Resistant starch is starch that ‘resists’ digestion in the small intestine and continues to the large intestine where it is fermented in the same fashion as fibre. It is higher in amylose than amylopectin, which is why it is digested more slowly.
Resistant starches (RS) have several health promoting properties. Like fibre, it contributes to faecal bulk, and improves insulin sensitivity. Resistant starch can aid in weight loss through promoting satiety and reducing the caloric intake. When resistant starch is fermented in the colon, the short-chain fatty acid butyrate is produced which may aid in the prevention of colon cancer. Resistant starch feed our microbiome (healthy gut bacteria), the short-chain fatty acids (SCFAs) are believed to prevent pathogens from taking hold, improve nutrient absorption, and aid immunity.
There are three types of RS:
It seems we can tolerate up to about 40-45 g/d of RS without it upsetting tummies. Too much and we can get bloating, gas and diarrhoea, the ratio of the various RS can have an influence too. Ideally RS is best consumed when it is in a solid form and part of a meal. Seems about 20 g/d is dandy for most of us, which is no sweat to gain if you eat a diet rich in whole foods or plant-based diet
Some examples of high resistant starch foods are:
Tips for the optimal starch inclusive diet
If you’re interested in the WCRF report, the whole document including the cancer prevention guidelines can be viewed here-
Words by Iydi Willis
Nutritionist and Health Education Consultant
Edited by Leanne Cooper
Registered Nutritionist, mother of two, author, educator, presenter and nutrition consultant.
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