Why Does Our Food Need to Be Digested?

Our body must digest food because most food components are too large and complex to be absorbed directly into the blood; digestion breaks them down into simpler, usable forms. Food contains carbohydrates, proteins, fats, vitamins, minerals, water, and roughage. Carbohydrates, proteins, and fats are made up of large molecules that cannot pass through the walls of the intestine. Digestion changes these into smaller molecules: carbohydrates into simple sugars, proteins into amino acids, and fats into fatty acids and glycerol. Vitamins, minerals, water, and roughage do not need digestion and are absorbed as they are. For example, when you eat rice (carbohydrate), your body must convert it into glucose before it can be used for energy. Many students think all food is ready for use as soon as it enters the stomach, but only digested, simple forms can be absorbed and used by the body.

The five steps of nutrition are ingestion, digestion, absorption, assimilation, and egestion, and each plays a specific role in how our body processes food. Ingestion is taking food into the mouth. Digestion is breaking down complex food into simpler, soluble forms. Absorption is the process where digested food passes through the wall of the intestine into the blood. Assimilation is the use of absorbed food by body cells for energy, growth, and repair. Egestion is the removal of undigested and unabsorbed food from the body. For example, when you eat a chapati, you ingest it, your digestive system breaks it down, the nutrients are absorbed into your blood, your muscles use the glucose for energy, and the leftover fibre is removed as waste. Some students confuse absorption and assimilation, but absorption is about entry into the blood, while assimilation is about actual use by cells.

The four types of teeth are incisors, canines, premolars, and molars, and each has a different role in chewing food. Incisors are the front, flat teeth used for cutting food. Canines are pointed teeth next to the incisors, used for tearing food. Premolars, located behind the canines, have flat surfaces with ridges for crushing and grinding. Molars are the largest teeth at the back, also used for grinding food into smaller pieces. Children have 20 milk (temporary) teeth, which are replaced by 32 permanent teeth, including four wisdom teeth that appear later. For example, when you bite into an apple, you use your incisors to cut it, your canines to tear it, and your premolars and molars to grind it before swallowing. Many students think milk teeth and permanent teeth are the same, but milk teeth fall out and are replaced by larger, stronger permanent teeth.

A tooth has three main parts: the crown (visible part above the gum), the neck (where the crown meets the gum), and the root (embedded in the jaw). The outermost layer is the hard enamel, which protects the tooth. Beneath the enamel is dentine, a bonelike layer. The pulp cavity, inside the dentine, contains nerves and blood vessels. The root is covered by cement, which helps anchor the tooth in the jaw. Dental caries (tooth decay) is caused by plaque—a sticky layer of food particles and bacteria that forms on teeth. Bacteria in plaque break down sugars, producing acids that damage enamel and cause cavities. To keep teeth and gums healthy, brush twice daily, avoid too many sugary foods, and rinse your mouth after eating. For example, eating sweets and not brushing can lead to plaque and tooth decay. Some students believe brushing once a day is enough, but regular cleaning is needed to prevent plaque buildup.