Carbohydrates and proteins

Carbohydrates are organic compounds consisting of the elements carbon, hydrogen, and oxygen. The elements are arranged in small molecules called saccharides. Carbohydrates are classified as either simple or complex, based on the number of saccharides they contain.
Starch (polysaccharide)is a carbohydrate consisting of a large number of glucose units joined together by bonds.
Simple carbohydrates contain just one or two saccharides. They are all sugars. Examples of sugars in the diet include sucrose, which is found in sugar cane, and lactose, which is found in milk. The main function of simple carbohydrates is to provide the body with energy. One gram of carbohydrate provides four kilocalories of energy. Glucose is the sugar that is used most easily by cells for energy. It circulates in the blood, providing energy to cells throughout the body. Glucose is the only source of energy used by the brain.
Complex carbohydrates, called polysaccharides, generally contain many saccharides. They include starches and fiber. Starches are found in plant foods such as vegetables and grains. They are broken down during digestion to form sugars that provide energy. Fiber consists of indigestible polysccharides and other materials such as cellulose. It is present in all plant foods.
Fiber is important because attracts water as it passes through the large intestine. This helps keep waste moist and moving easily through the intestine. Fibre prevents constipation, which is small, hard and dry faeces that are hard to pass.

Proteins are relatively large organic compounds containing carbon, hydrogen, oxygen, and nitrogen. The elements are arranged in small molecules called amino acids. Amino acids are the building blocks of proteins. They bond together to form long chains, called polypeptides. Proteins consist of one or more polypeptides.

Proteins play many vital roles in the body, including:
• Making up the majority of muscle tissue.
• Regulating many body processes.
• Forming antibodies that destroy bacteria and other “foreign invaders.”
• Transporting nutrients and other vital substances in the blood (Haemoglobin transport O 2 in blood).
Dietary proteins are broken down during digestion to provide the amino acids that cells need to make proteins for the body. Twenty different amino acids are needed for this purpose. Nine of these amino acids cannot be synthesized by cells from simple components and must be obtained from foods. They are called essential amino acids because they are essential in the diet.
Proteins that contain all ten essential amino acids are referred to as complete proteins. They are found in animal foods such as milk and meat. Proteins that are missing one or more essential amino acids are referred to as incomplete proteins. They are found in plant foods such as legumes and rice. By eating a variety of different plant foods containing incomplete proteins, you can include all ten essential amino acids in your diet.
One gram of protein provides four kilocalories of energy. This is the same amount of energy that one gram of carbohydrate provides.