Learning objectives • To understand that macronutrients are needed by the body. • To know the functions and sources of carbohydrate, protein and fat. • To understand the consequences of malnutrition of carbohydrate, protein and fat.
Macronutrients The macronutrients are: • carbohydrate; • protein; • fat.
Function and sources of carbohydrate Carbohydrate provides the main source of energy for the body. Some forms of complex carbohydrates may reduce cholesterol which is beneficial for health.
Further classification of carbohydrate • There are different ways to classify carbohydrate. • One method is into: • sugar; • starch.
Classification of carbohydrate Sugar Monosaccharides are the simplest form of carbohydrate molecules, e.g. glucose, fructose and galactose. Disaccharides are formed when two sugar molecules join together, e.g. sucrose (glucose and fructose), lactose (glucose and galactose) and maltose (2 molecules of glucose). Starch Polysaccharides are made up of many monosaccharide's molecules joined together, e.g. starch, glycogen, cellulose and pectin.
Another classification systems for sugars Intrinsiccan be described as sugars incorporated into the cellular structure of food, e.g. sugars in whole fruits and vegetables. Extrinsic sugars can be described as not bound into cellular structure, e.g. lactose in dairy products. Non-milk extrinsic sugars (NMES) are sugars not bound into cellular structure and also not found in milk, e.g. honey, fruit juices, table sugar and confectionery are all examples of foods containing NMES.
Excessive consumption of carbohydrate Increased body weight When too much carbohydrate is consumed and not used for energy over an extended period of time, it is stored as fat. Building up too much fat will increase body weight. Increase dental caries It is important that teeth are brushed twice a day and foods high in sugar should be eaten with main meals, rather than in between snacks to prevent dental caries.
Lack of carbohydrate The short term effects of a lack of carbohydrates are weight loss and lethargy. Kwashiorkor and Marasmus are two forms of deficiency disease which can develop in extreme conditions. These occur where energy and protein are lacking in the diet over an extended period of time.
Protein Protein is needed for growth, development and repair of the body. Excess protein can be broken down and used as a source of energy. Protein is made up of different combinations of amino acids. These are the building blocks of protein. Amino acids are compounds containing carbon, hydrogen, oxygen, nitrogen and, in some cases, sulphur.
Indispensable or dispensable? The human body is able to make most amino acids itself and these are known as non-essential or dispensable amino acids. There are some amino acids that cannot be made by the body. They are called indispensable amino acids (IAA) or sometimes essential amino acids. It is essential that these are provided in the diet as the body cannot make them.
Body needs Adults only need 8 indispensable amino acids for growth and repair. Children need to obtain 10 indispensable amino acids.
Biological value and complementation It is not just the amount of protein, but the quality or biological value of the protein that needs to be considered. If a protein contains all the indispensable amino acids it is said to have a high biological value. If a protein does not contain all the indispensable amino acids it is said to have a low biological value. The amino acid that is in the shortest supply in relation to need is termed the limiting amino acid.
High and low biological value High biological value (HBV) proteins include: meat, fish, eggs, cheese, and milk. Low biological value (LBV) proteins include: cereals, pulses, some nuts and vegetables. In general, animal protein sources have a higher biological value, than vegetable sources. Vegetarians and vegans need to eat wisely to ensure they are getting all the indispensable amino acids.
Protein complementation Complementation of low biological value (LBV) protein sources ensures that all essential amino acids are consumed. Amino acids of one protein source can compensate for the limitations of the other, resulting in a combination to create a high biological value meal.
An example of protein complementation Two foods providing vegetable protein are eaten at a meal e.g. a cereal (bread) and a pulse (baked beans). The amino acids of one protein compensates for the limitations of the other. This results in a combination of higher biological value.
The body’s needs for protein Babies and children have a high need for protein because they are growing. Adolescents need protein for their rapid growth spurt. Pregnant women need more protein than other adults because of the growing baby. Nursing mothers also need more protein for lactation.
Protein deficiency Protein deficiency is rare, but there is a condition called PEM – protein energy malnutrition. This can be seen in infants with stunted growth or thin arms and legs, and large distended abdomens. Marasmus - this condition mainly affects infants causing them to become thin and weak. The body adapts to the shortage of energy and nutrients. All energy stores are depleted as it is used to supply vital organs. Kwashiorkor - this condition is known to be the body’s adaption to shortage of energy and nutrients.
Fat Fat performs many functions in the body including: • providing essential fatty acids; • providing a concentrated source of energy; • carrying fat soluble vitamins and is important for their absorption; • surrounding and protecting body organs; • forming an insulating layer keeping the body warm. Fat is made up of fatty acids and glycerol. Fatty Acid 1 Fatty Acid 2 Fatty Acid 3 Glycerol
Essential fatty acids The body can make most fatty acids. Essential fatty acids (EFA) are required for important functions in the body. These must be provided by the diet because our bodies cannot make them.
Sources of saturated and unsaturated fats • Saturated fat Meat, coconut oil, palm oil, cakes and biscuits, lard. • Unsaturated fat * Mono unsaturated fat Rapeseed oil, avocado and olive oil. * Polyunsaturated fat Oily fish, sunflower oil and pine nuts.
Over consumption of fat Eating too much saturated fat has become a problem in our society. There are many health problems linked with too much saturated fat in the diet, e.g. coronary heart disease, and strokes.
Review of the learning objectives • To understand that macronutrients are needed by the body. • To know the functions and sources of carbohydrate, protein and fat. • To understand the consequences of malnutrition of carbohydrate, protein and fat.
For more information visit www.nutrition.org.ukwww.foodafactoflife.org.uk