There is an old saying, “you are what you eat”. Does this mean that the human body is made of apples, pizzas, chicken, peas, ice cream and countless other foods? Amazingly, yes it does. It is built up from very small pieces of matter that come from the foods we eat. The study of foods—which ones are healthy and which are not, and what happens to them in the body—is called nutrition.
TAKE APART, PUT BACK TOGETHER
Sometimes old buildings are not simply knocked down and destroyed. Instead, they are carefully taken apart into separate pieces, including bricks, lengths of wood, roof tiles, and other parts. These building materials can then be put back together to make another building with a different design.
The same sort of process happens inside your body. The foods you eat are broken down, or digested, inside your body into smaller and smaller pieces. These are called nutrients. The nutrients are carried around your body in your blood, to be used as building materials. They are joined together to make new body parts. Some of them are used for growth, as the body gets bigger. Some are used to replace old and worn out bits, since body parts such as the skin do not last forever, and are constantly renewed and maintained by the body. Some nutrients are used to repair injuries and other damage to the body.
ENERGY FOR LIFE
The nutrients in foods do not just supply building materials, but also provide energy. All the life processes that take place inside the body need energy. The beating of the heart, breathing by the lungs, digestion in the stomach, the movement of the muscles and even thoughts and feelings in the brain must all be powered by energy. This energy comes from some types of nutrients in foods. Other kinds of nutrients supply the building materials. Certain nutrients can do both, depending on what foods are eaten and what the body’s needs are at the time.
TYPES OF NUTRIENTS
There are five major kinds, or groups, of nutrients. These are proteins, carbohydrates, fats, vitamins, and minerals. Different foods contain different amounts of each of these nutrients.
Proteins are the most important nutrients as building materials, for growing and repairing body parts, from the skin to bones. They are needed especially for strong muscles. Proteins are found in meats, poultry, and fish, and also in eggs, cheeses and other dairy products, and in some vegetables and fruits.
Starchy or sugary foods are rich in carbohydrates. Their main use is for energy. Carbohydrates are broken down to form glucose sugar, which is the body’s main source of energy for all its life processes. Bread, rice, potatoes, pasta and various fruits and vegetables contain carbohydrates.
Oils and fats, called lipids, can also be broken down to provide energy. Small amounts are needed to keep body parts, such as nerves, working well. Plant-based oils such as sunflower, safflower, soya, olive, and corn oils are the healthiest. Less healthy are fats from animal foods, especially those in fatty and processed meats.
Vitamins and minerals
The body needs about 15 vitamins and 10 main minerals to stay healthy. Minerals include iron for the blood and calcium for strong bones and teeth. Examples of vitamins are vitamin K, needed for blood to clot properly at a cut and vitamin C, which is important in maintaining all kinds of body parts, including the skin, lips, and gums. Most vitamins and minerals are especially plentiful in fresh fruits and vegetables.
Another helpful substance in foods is fibre, also called dietary fibre or roughage. It occurs mainly in wholemeal types of bread, pasta, rice and other grain or cereal foods, and also in fresh vegetables and fruits. Fibre is not digested and absorbed into the body. But it does keep the digestive system or guts working well, especially the intestines, and it helps prevent some intestinal diseases.
The body is two-thirds water, and this water is constantly moving around in body parts and being used up. Water is contained in most foods, and it makes up most of our drinks. An average adult should take in about two and a half litres of water each day. Lack of water is called dehydration and is very dangerous. It can cause illness and death far faster than lack of food can.
THE PROCESS OF DIGESTION
The parts of the body that break down or digest foods to obtain their nutrients are called the digestive system. Digestion begins in the mouth, where teeth cut and crush the food, and mix it with watery saliva (spit). Lumps of chewed food are swallowed down the gullet (oesophagus) into the stomach. Here powerful digestive juices and acids are added to the food, as the stomach squeezes and churns it up.
Next, the food passes into the long, coiled small intestine. More digestive juices are added. These juices come from the small intestine’s inner lining and also from body parts called the pancreas and liver, which are next to the stomach. Nutrients that are removed from the food by these juices are taken from the small intestine into the blood.
After the small intestine comes the shorter but wider large intestine (colon). Here water is removed from the leftovers and they are formed into brown, squishy lumps. The lumps, called faeces or bowel motions, are stored in the last part of the intestine, the rectum. Finally, they leave the body through a ring of muscle, called the anus.
A balanced diet includes a wide range of foods that provide all the nutrients needed by the body, in the right proportions, but not too much of them. It includes plenty of fresh foods, especially fresh fruits and vegetables. It also means not eating too many fatty foods, particularly fatty meats.
Too much of certain foods can cause ill health and diseases of the stomach, intestines and other body parts. Also, eating too much food, and taking too little exercise, makes the body too heavy, or overweight. This is known as obesity. Obesity increases the risks of many health problems, from painful joints to high blood pressure and heart disease.