You may not think of it this way, but digestion begins in your mouth. Chewing your food thoroughly breaks it into smaller pieces, making more of its surface area accessible to digestive juices. Saliva is an integral part of that digestive process, supplying enzymes that dismantle starches and fats.
Saliva performs many functions. The watery or serous component of saliva moistens your food, making it easier to taste and preparing it for swallowing. Saliva's slippery texture comes from a specialized type of mucus that lubricates the inner surfaces of your mouth and makes swallowing food easier. Within these fluids are various enzymes -- proteins that act as catalysts for chemical reactions. Enzymes are highly specific and react with only a narrow range of substances, so saliva contains numerous enzymes to handle the many jobs it must do.
Amylase, an enzyme that turns complex starches into simple sugars, is the most prevalent digestive juice in saliva. Your pancreas also produces amylase, but starch digestion begins in the mouth with salivary amylase. When you bite into a piece of bread, the serous component of saliva carries the salivary amylase into the food's porous structure as you chew. The enzyme dismantles the long-chain molecules of the starch into simpler carbohydrates, more commonly known as sugars. Everyone produces slightly different volumes of salivary amylase, and the speed with which your saliva breaks down starches influences how you perceive the taste and texture of your food.
Until relatively recently, scientists thought that fat digestion didn't start until food reached the stomach. However, the 1973 discovery of the fat-digesting enzyme lipase in saliva revealed that fats, like starches, start the digestion process in the mouth. Also produced in the pancreas, lipase breaks down fats and oils into their constituent fatty acids and glycerol molecules. Newborn babies rely on the lipase in their saliva to help them digest the fats in milk, but adults also produce lipase to help them digest dietary fat. Researchers are investigating how lipase in your saliva can help with pancreatic lipase insufficiency.
Saliva plays an integral role in protecting your teeth from decay with lysozyme, an enzyme that digests the harmful bacteria that would otherwise colonize your teeth and tongue. Medications that dry your mouth leave you at greater risk of developing dental cavities because too little saliva means too little lysozyme interacting with bacteria in your mouth. It's important to brush shortly after you wake up because your saliva production decreases overnight, giving bacteria a chance to get ahead of lysozyme production.
- Colorado State University Hypertexts for Biomedical Sciences: Salivary Glands and Saliva
- PLoS ONE: Individual Differences in AMY1 Gene Copy Number, Salivary α-Amylase Levels, and the Perception of Oral Starch
- Nutrition: Lingual and Gastric Lipases
- National Institute of Dental and Craniofacial Research: Dry Mouth
Lauren Whitney covers science, health, fitness, fashion, food and weight loss. She has been writing professionally since 2009 and teaches hatha yoga in a home studio. Whitney holds bachelor's degrees in English and biology from the University of New Orleans.