Nutrition in Humans PDF

# Nutrition in Humans ## Why do we need food? - To supply us with a 'fuel' for energy - To provide materials for growth and repair of tissues - To help fight disease and keep our bodies healthy ## Balanced Diet It is the diet that contains carbohydrates, lipids, proteins, minerals and vitamins -...

# Nutrition in Humans ## Why do we need food? - To supply us with a 'fuel' for energy - To provide materials for growth and repair of tissues - To help fight disease and keep our bodies healthy ## Balanced Diet It is the diet that contains carbohydrates, lipids, proteins, minerals and vitamins - along with dietary fibre and water in the right amounts. ### Carbohydrates #### Sugars ##### Sources - Glucose is found naturally in many sweet-tasting foods, such as fruits and vegetables. - Fructose in fruits. - Lactose in milk. - Sucrose is the main sugar that is transported through plant stems. This is why we can extract it from sugar cane. - Digestion of starch provides sugar. #### Physical Properties - Sweet in taste - Soluble in water #### Functions They supply cells with energy. Cells release energy by oxidizing glucose, in the process of cell respiration. ### Starch - Starch is a large, insoluble molecule. - Because it does not dissolve, it is found as a storage carbohydrate in many plants, such as potato, rice, wheat and millet. The staple diets of people from around the world are starchy foods like rice, potatoes, bread and pasta. - Starch is a polymer of glucose - it is made of long chains of hundreds of glucose molecules joined together. - Starch is only found in plant tissues. ### Notice - **Glycogen:** Animal cells sometimes contain a very similar carbohydrate called glycogen. - This is also a polymer of glucose, found in tissues such as liver and muscle, where it acts as a store of energy for these organs. - Large carbohydrates such as starch and glycogen have to be broken down into simple sugars during digestion, so that they can be absorbed into the blood. ### Cellulose - The material that makes up plant cell walls. - Humans are not able to digest cellulose, because our gut doesn't make the enzyme needed to break down the cellulose molecule. This means that we are not able to use cellulose as a source of energy. #### Importance - It forms dietary fibre or roughage, which gives the muscles of the gut something to push against as the food is moved through the intestine. This keeps the gut contents moving, avoiding constipation. - Helps prevent serious diseases of the intestine, such as colitis and bowel cancer. ## Lipids ### Sources and Properties #### Fats - Derived from animals. - Solid at room temperature. - Have high melting points. - Sources: meat, milk, butter, ghee, eggs and oily fish. #### Oils - Derived from plants. - Liquid at room temperature. - Have low melting points. - Sources: olive oil, cotton seed oil, corn oil and margarine. ### Functions - **Body mass:** Lipids make up about 10% of our body's mass. - **Cell membrane:** They form an essential part of the structure of all cell membranes. - **Store of energy:** Fat is deposited in certain parts of the body as a store of energy, for example under the skin and around the heart and kidneys. - **Insulation:** The fat layer under the skin acts as insulation, reducing heat loss through the surface of the body. - **Protection:** Fat around organs such as the kidneys also helps to protect them from mechanical damage. ### Notice Although lipids are an essential part of our diet, too much lipid is unhealthy, especially a type called saturated fat, and a lipid compound called cholesterol. ## Proteins ### Sources - **Animal sources:** Meat, fish, cheese, eggs. - **Plant sources:** Beans, peas, nuts. ### Functions - Growth. - Repair of damaged tissues. - Many compounds in our bodies are made up of proteins as enzymes. ### Recommended Amounts About 70 g daily. ### Lack of Protein This results in protein deficiency diseases - Kwashiorkor. ## Minerals | Mineral | Role in the body | Found in | |---|---|---| | Calcium | Making bones and teeth | Dairy products, fish, bread, vegetables. | | Phosphorous | Making bones and teeth | Most food | | Sodium | In body fluids as blood | Common salt and most food. | | Chlorine | In body fluids as blood | Common salt and most food. | | Magnesium | Making bones, found inside the cells. | Green vegetables | | Iron | Part of haemoglobin in red blood cells, carry oxygen. | Red meat, eggs, liver, spinach. | ### Mineral Deficiency Diseases - **Rickets:** Due to deficiency of calcium. There is poor bone development, which leads to deformity of bones. - **Anaemia:** Due to deficiency if iron. Haemoglobin is not enough is red blood cells. Anaemic persons are always tired with lack of energy. ## Vitamins | Vitamin | Sources | Role in the body | |---|---|---| | A | Carrots, liver, fish liver oil. | Makes a chemical in the retina, protects the surface of the eye. Needed for vision specially in the dark. | | C | Fresh fruits and vegetables. | Sticks together cells lining surfaces such as the mouth. | | D | Fish liver oil, made in skin in sunlight | Helps bones absorp calcium and phosphate. | ### Vitamin Deficiency Diseases - **Vitamin A deficiency** - Night blindness. - Damaged cornea of the eye - **Vitamin C deficiency** - Scurvy - wounds fail to heal and bleeding occurs in many places of the body. - **Vitamin D deficiency** - Rickets - Poor teeth ## Water - In water and juices. - Needed for all chemical reactions in the body. ## Energy Requirements ### Factors Affecting Energy Requirements - **Age:** Energy requirements increase as we approach adulthood. Energy needs of adults decrease as they age. - **Activity level:** Activity needs more energy, as muscle contraction needs more respiration to produce more energy. - **Pregnancy:** Energy requirements increase to support growth of the foetus. Energy needs increase due to the extra mass of the foetus. ## Practical ### To Investigate the Energy Content of a Food Sample **Procedure** - Weigh the mass of the food sample. - 20 cm³ of water is placed in a boiling tube supported in a clamp on a stand. - The temperature of the water is recorded. - The food is speared on the end of a mounted needle, and then held in a Bunsen burner flame until it catches fire. - When the food is alight, the mounted needle is used to hold the burning food underneath the boiling tube of water so that the flame heats up the water. - This is continued, until the food will no longer burn. - The final temperature of the water is measured, using the thermometer to stir the water gently, to make sure that the heat is evenly distributed. #### Notice - The energy needed to raise the temperature of one gram of water by 1°C is 4.2 joules - The volume of 1 cm³ of water has a mass of one gram. #### Calculation Energy in joules per gram of food substance = (Final temperature - temperature at start) x 20 x 4.2 / Mass of food (g)