88 The term protein derives from the Greek word pr tos, which means first or primary. This emphasises the fundamental role of proteins in life and nutrition. What is pH? There are two types of fibre: soluble fibre (which dissolves in water and helps lower cholesterol) and insoluble fibre (which adds bulk to stool and aids in digestion). PROTEINS AND CARBOHYDRATES Proteins and carbohydrates are crucial for building and repairing tissues, supporting muscle growth, producing enzymes and hormones, and serving as the body s primary energy source. Proteins Proteins are made up of chains of amino acids. Twenty amino acids are fundamental for protein formation, but only eight of them are considered essential and must be obtained through food such as meat, fish, eggs, and legumes. Depending on their origin, proteins are classified as animal or plant-based. Animal proteins contain all amino acids, while plant proteins do not contain them all, unless legumes and cereals are consumed together. The amount of proteins to be consumed daily can vary from 1g to 2g per kg of body weight, i.e. 12-20% of the total daily caloric intake. Liver, pancreas, muscles, and the immune system are the organs involved in the synthesis of proteins. Functions of proteins Structural function: they build and maintain tissues like muscles, skin, hair, and nails through collagen and keratin. bowel: intestino, viscere bulk: volume gut: intestino leafy green vegetables: verdure a foglia verde liver: fegato oats: avena starch: amido stool: feci sucrose: saccarosio 166 SCIENCE AND PHYSICS Enzymatic function: they act as enzymes to speed up biochemical reactions (e.g. digestive enzymes like amylase and pepsin). Transport function: they carry molecules like oxygen and nutrients throughout the body. Hormonal function: they regulate body functions (e.g. insulin controls blood sugar). Immune defence function: they produce antibodies to fight infections. Energy source function: they serve as energy source when carbohydrates and fats are insufficient. Regulatory function: they help maintain fluid balance and pH levels in the body. Carbohydrates Carbohydrates, also known as saccharides or sugars, are compounds made up of carbon, hydrogen, and oxygen. They are the body s primary source of energy and some of them, like fibre , help digestion by promoting healthy bowel movements and supporting intestine s health. They are divided into: simple sugars, which are composed of a single molecule, such as glucose, fructose (the sugar in fruits and honey), and galactose (the sugar in milk), and which are digested very quickly; complex sugars, which are made up of two disaccharides (like sucrose, or table sugar) or more polysaccharides (like starch) simple sugars, and which are found in flour, corn, rice, legumes, and tubers. Before being used as an energy source, they have to be converted into glucose by the liver.