Sugars are the term we use to describe a carbohydrate that contains just one or two sugar molecules. For obvious reasons, these sugars are often called simple carbohydrates. Some examples of carbohydrates with one sugar molecule, called monosaccharides, include glucose, fructose (from fruits) and galactose (from milk products). Some examples of carbohydrates with two sugar molecules, called disaccharides, include sucrose (from table sugar), lactose (from dairy) and maltose (found in beer and some vegetables). We are able to absorb monosaccharides directly into the bloodstream as they are the simplest structure of carbohydrate, however the liver then converts the monosaccharides into the body’s preferred energy source, glucose. Disaccharides need to be broken down into monosaccharides in the gastro-intestinal tract before they can be absorbed into the bloodstream.
Starches refer to carbohydrates that contain three or more sugar molecules and are also known as polysaccharides. Foods that are high in starch include whole-wheat bread, cereal, corn, oats, rice, legumes, beans, peas, lentils, and potatoes. Similar to disaccharides, the polysaccharides in starches need to be broken down into simple sugars before they can be absorbed however as the sugar molecules in starches are more complex than sugars, the digestion process typically takes longer.
Finally, fiber is a plant-based type of carbohydrate that cannot be broken down into digestible sugar molecules. There are two type of fiber: soluble and insoluble. Soluble fiber binds with the moisture in your digestive system to form a soft gel that helps slow the absorption of nutrients and is then broken down into short-chain fatty acids to provide your body with energy. Insoluble fibers travel through the intestine with very little change and whilst they do not get digested, they are important for increasing bulk, softening your stools, and shortening the transit time of food through the gastro-intestinal tract. Food sources that are high in fiber include fruits, vegetables, nuts, beans and whole grains.
Foods that are rich in starch and fiber are considered to be complex carbohydrates. They pack more nutrients and take longer to digest than simple carbohydrates which means that they are more filling, increase satiety, reduce overeating and support weight loss. Complex carbohydrates have also been shown to promote better digestive health, help lower cholesterol and decrease the risk of heart disease.