Glycans in Food: From Energy to Gut Health

Glycans are a major component of the human diet, representing a diverse group of complex carbohydrates. Found in foods ranging from fruits and vegetables to grains and legumes, these molecules are constructed from long chains of sugar units, or monosaccharides. This structural complexity distinguishes them from simple sugars, such as the glucose or fructose you might find in candy or soda. While simple sugars are small molecules, glycans are large polysaccharides, and this difference in size and structure dictates how they are processed in the body.

Common Glycans Found in Food

The foods we eat contain a wide variety of glycans, which can be broadly sorted into two main categories based on how our bodies process them. The first category, digestible glycans, consists almost entirely of starches. Starches are long, often branched chains composed exclusively of glucose molecules. They serve as the primary energy storage form in plants and are abundant in staple foods such as potatoes, rice, corn, and wheat products like bread and pasta.

The second category is non-digestible glycans, more commonly known as dietary fiber. This group includes cellulose, a primary component of plant cell walls, found in leafy greens, vegetable stalks, and whole grains. Pectins, another type of fiber, are abundant in fruits like apples, oranges, and lemons, where they provide structural integrity. Other notable non-digestible glycans include inulin, a prebiotic fiber found in onions, garlic, and chicory root, and chitin, which is sourced from the cell walls of fungi like mushrooms.

Digestible Glycans and Energy Metabolism

The primary role of digestible glycans like starch is to provide the body with energy. This process begins in the mouth, where amylase in saliva starts to break down starch chains into smaller sugar molecules. The digestion continues in the small intestine, where pancreatic amylase completes the process, breaking the starch down into individual glucose units.

Once broken down, these glucose molecules are absorbed through the intestinal wall and into the bloodstream. This provides a source of fuel for cells throughout the body, powering everything from muscle contractions to brain activity. If the energy is not needed immediately, the body can store the excess glucose in the liver and muscles in the form of glycogen for later use.

Functions of Non-Digestible Glycans

Non-digestible glycans, or dietary fibers, travel through the digestive system largely intact since the human body lacks the enzymes to break them down. Many types of fiber are highly absorbent and swell with water, which adds bulk to the contents of the stomach and intestines. This process contributes to a feeling of fullness, or satiety, which can help in managing appetite. This added bulk also plays a part in maintaining regular bowel movements by increasing the weight and softness of stool, which helps prevent constipation.

Soluble fibers, such as the pectins found in fruit, can form a viscous, gel-like substance in the gut. This gel slows down the absorption of other nutrients, including sugars and fats, which can help in moderating blood sugar spikes after meals and may influence cholesterol levels.

Glycans as Prebiotics for Gut Microbiota

When non-digestible glycans reach the large intestine, they become a resource for the microorganisms that reside there, known as the gut microbiota. These glycans function as prebiotics, which are compounds that nourish beneficial gut bacteria, promoting the growth and activity of helpful microbes.

The gut bacteria break down these complex carbohydrates through a process called fermentation. This bacterial digestion releases beneficial compounds, most notably short-chain fatty acids (SCFAs) such as butyrate, propionate, and acetate. These SCFAs are important for gut health; butyrate serves as the primary energy source for the cells lining the colon, helping to maintain the gut barrier and influence the immune system.