Transcript U2.1P2.Diet
A balanced diet and the 7 food groups • Aims: – To know why food is important – To know that a healthy diet consists of a balance of 6 groups of chemicals and water – To be able to use chemical tests to identify proteins, carbohydrates and fats Diet • Your diet is the food you eat every day. • You could have a poor diet or a healthy diet. • Your food is a source of raw materials for your body. • These raw materials are needed to make new substances for: – Energy – Growth – Health Why do we need food? Humans need to consume a balanced diet which contains a variety of different types of food. The main nutrients the body needs are: carbohydrates for energy; proteins for growth and repair; fats to store energy; vitamins and minerals to keep the body healthy; fibre to keep your intestines healthy and prevent constipation; water is an important solvent in your body. It has many used. The amount of each food type needed is related to the proportions in the food pyramid. Which food type does the body need the most of? Nutrients in food What is a balanced diet? What are carbohydrates? Starchy foods contain carbohydrates which are made of long chains of identical small sugar molecules. carbohydrate molecule one sugar molecule The long chains of carbohydrates are broken down into the smaller sugar molecules by the body. The small molecules from carbohydrates are used by the body to release energy and make the body work. What are proteins? Proteins, like carbohydrates, are made of long chains of small molecules. In proteins, these small molecules are not identical. protein molecule one amino acid Proteins are made up of chains of small molecules called amino acids. There are over 20 different kinds of amino acid. Proteins are used by the body for growth and repair. What are fats? Fats are made up of fat molecules which contain fatty acids and glycerol. fat molecule fatty acids glycerol Fat molecules have to be broken down by the body so that they can be used for energy storage. Fats are also used by the body to keep heat in and to make cell membranes. Food types Type Found in Uses Carbohydrates Bread, potatoes, cereal Energy Fats Cream, butter, milk, oil A store of energy Proteins Meat, fish, eggs Building and repairing cells Vitamins Vegetables, cereal Keep things “ticking over” Minerals Meat, milk, cereal Strong teeth etc Fibre Fruit + veg, cereal Keeps you regular! Water Water! 75% of the body is water What problems can diet cause? • Too much food: – Weight gain – Heart disease • Too little food: – Weight loss – Lack of energy • Too little protein: – Muscle wastage – Kwashiorkor What problems can diet cause? • Too little vitamin C: – Scurvy • Too little vitamin D: – Rickets • Too little calcium: – Weak bones and teeth Food tests 1 To investigate what happens in digestion we need to be able to test for different foods. Here are two simple tests: 1) The test for starch: Drop some iodine onto the food. If the iodine turns BLUE/BLACK then STARCH is present. 2) The test for simple sugars (e..g glucose) Boil the food with some Benedict’s solution. If an orange “precipitate” appears then the food contains simple sugars Iodine Food tests 2 1) The test for protein: Place 1 cm of food at the bottom of a test tube. Add 5 drops of Biuret solution. If protein is present it will turn lilac/purple 2) The test for fats: Shake the food with about 10cm3 of ethanol in a test tube. Pour some of the solution into a tube containing water. If fat is present the water will turn cloudy white.