What is starch?

Starch is a complex polysaccharide made up of glucose molecules. It is one of the most common carbohydrates found in nature and is the primary energy source for many organisms, including humans. Starch is found in many staple foods such as bread, potatoes, rice, and pasta.

When it comes to human health, starch can have both positive and negative effects. On the one hand, consuming moderate amounts of starch provides the body with a slow release of energy throughout the day. This can help to regulate blood sugar levels and keep you feeling full for longer. Additionally, some studies have shown that consuming high-fibre starches, such as those found in whole grains, can reduce the risk of developing chronic conditions such as type 2 diabetes, heart disease, and colon cancer.

On the other hand, consuming excessive amounts of refined starches, such as white bread and sugary snacks, can have a negative impact on health. These foods are quickly digested, leading to a rapid spike in blood sugar levels. Over time, consuming too much refined starch can contribute to weight gain, insulin resistance, and an increased risk of chronic health conditions.

Refined starch refers to starch that has been processed to remove the outer layers of the grain, including the bran and germ, which contain most of the fiber, vitamins, and minerals. This processing makes the starch easier to digest and provides a more rapidly absorbed source of energy. 

Refined starches have a high glycemic index, which means they are quickly broken down into glucose and can cause a rapid spike in blood sugar levels. This can lead to insulin resistance, weight gain, and an increased risk of chronic health conditions over time.

In contrast, unrefined or whole grain starches contain the entire grain, including the bran and germ, which slow down the digestion of starch and provide a more gradual release of energy. These starches have a lower glycemic index and are a better choice for optimising health.

How are starches broken down?

The breakdown of starch in the human digestive system begins in the mouth with the enzyme amylase, which is produced by the salivary glands. Amylase breaks down the large starch molecules into smaller maltose and glucose units. As the food travels down the digestive tract, more amylase is added in the small intestine from the pancreas.

In the small intestine, the maltose and glucose units are further broken down by other digestive enzymes such as sucrase, lactase, and isomaltase into monosaccharides that can be absorbed by the intestinal epithelial cells and transported into the bloodstream.

The remaining undigested starch is transported to the large intestine, where it is fermented by gut microbiota, producing vitamins and short-chain fatty acids that can be absorbed and used as a source of energy.

The breakdown of starch into glucose requires the presence of multiple enzymes working together in a specific order to achieve efficient digestion. Any defects in the expression or function of these enzymes can lead to starch malabsorption, leading to digestive disorders such as lactase deficiency and sucrose-isomaltase deficiency.

In conclusion, starch can be a beneficial source of energy and fiber when consumed in moderation and as part of a balanced diet. Whole grain foods and other high-fiber starches are the best options for optimizing health, while excessive consumption of refined starches should be avoided. Digestion starts in the mouth and continues through the small intestine. Undigested starches are fermented in the large intestine contributing vitamins and short-chain fatty acids for cellular energy.