Human Nutrition: Process, Nutrients, and Infant Feeding
The Nutrition Process: Ingestion, Digestion, Absorption, and Expulsion
Ingestion
Ingestion involves the mechanical and chemical preparation of food before it enters the stomach:
- Chewing (Mastication): This is the crushing and fragmentation of food, carried out by the tongue and the teeth.
- Insalivation: This is the impregnation of food with saliva, secreted by the salivary glands, until it becomes a mass called the food bolus.
- Swallowing (Deglutition): The food bolus passes through the pharynx and esophagus until it reaches the stomach. This process is carried out by the pharynx and the esophagus.
Digestion and Initial Absorption
In the stomach, the food bolus is mixed with gastric juice, which contains hydrochloric acid. The acid destroys bacteria present in the food. The food bolus is finally transformed into a liquid substance called chyme.
Nutrient Absorption
Absorption is the crucial passage of digested nutrients from the digestive tract (primarily the small intestine) into the blood vessels and lymphatic system.
Expulsion (Elimination)
In the large intestine, water and remaining nutrients are absorbed. The non-absorbed matter is concentrated, forming feces (stool) that are subsequently expelled from the body.
Food and Energy Requirements
The body utilizes food to provide essential resources, including:
- Material for growth and development.
- Material to replace worn out or damaged tissues.
- Energy for the wide range of chemical activities (metabolism) that take place inside the body.
- Energy for physical activities.
- Heat to keep the body warm (thermoregulation).
Essential Food Substances (Nutrients)
All foods consist of one or more of seven types of substances: proteins, carbohydrates, fats, minerals, vitamins, fiber, and water. Nutrients are substances derived from foods that are essential for life.
Proteins
Proteins are used to build the body and keep it in good repair. They are especially important in childhood for building the brain, muscles, skin, blood, and other tissues in order to ensure a strong, healthy body.
Carbohydrates
Carbohydrates provide the primary source of energy. Starch and sugar are both forms of carbohydrates.
Fats (Lipids)
Fats may be in solid form, like butter, or in a liquid form, like oil, depending on the temperature. Fats provide concentrated energy. The body needs a certain amount of fat, but when more is consumed than is used, the extra energy becomes stored as body fat.
Minerals
Minerals are substances like calcium and iron which occur naturally in the earth. Fifteen minerals are known to be essential for the various chemical activities which take place in the body and to build and repair tissues. They are obtained from:
- Foods derived from plants, which absorb minerals from the soil.
- Foods derived from animals which have eaten plants.
- Drinking water, in which the minerals are dissolved.
The only minerals which are sometimes in short supply in the body are calcium, iron, and fluoride.
Key Minerals and Their Functions
- Calcium: Essential for strong bones and teeth.
- Iron: Essential for the formation of red blood cells.
- Fluoride: Helps to produce strong tooth enamel.
- Phosphorus: Has a wide variety of essential functions in cells and, together with calcium, is needed for strong bones and teeth.
Vitamins
Vitamins are complex chemical substances made by plants and animals. The human body cannot manufacture vitamins, so they have to be obtained from food. Only a very small quantity of each vitamin is required for the body to keep healthy and active.
Dietary Fiber (Roughage)
Dietary fiber consists of plant material which cannot be digested. It is present in vegetables, fruit, wholemeal bread, pulses (such as peas, beans, and lentils), and cereals (such as oats, wheat, and bran). Fiber encourages the movement of food through the intestines, which helps to prevent constipation.
Water
Water is the main substance in the body and accounts for about two-thirds of the body’s weight. It forms part of all body tissues and is the liquid in which the chemical activities in the body take place. Water is lost from the body through sweat, breath, and urine. It enters the body as part of solid food as well as in drinks.
Infant Nutrition: Feeding a New Baby
Breast Milk Benefits
Breast milk is the natural milk for babies, offering numerous advantages:
- It contains the right amounts of all the necessary food substances.
- It contains antibodies, providing immunity.
- The milk is always at the right temperature.
- It is easy for the baby’s body to digest.
- It is clean and safe.
Exclusive Breastfeeding Period
Breast milk is recommended exclusively for the first six months of life.
Bottle Feeding and Follow-on Milk
Bottle-fed babies should be given follow-on milk to drink until 12 months of age to prevent any risk of anemia.
Are Extra Vitamins Required?
Sometimes, vitamin drops are recommended. Fruit juice contains Vitamin C, but should be introduced cautiously.
Are Extra Minerals Required?
Milk contains all the minerals a baby needs for the first few months of life. Although milk is low in iron, a baby is born with several months’ supply stored in the liver.
Introducing Cow’s Milk
Cow’s milk should not replace baby milk or breast milk until the age of 12 months.
Is Extra Water Needed?
Breast milk contains all the water a baby needs, unless the weather is extremely hot.