Nutrition PDF

NUTRITION SESSION OBJECTIVES Define the term nutrition and list the components of the nutrients in the diet. Explain the caloric value of carbohydrates, lipids and proteins. Define the Basal Metabolic rate and calculate the daily energy requirements. Describe the digestion and absorptio...

NUTRITION SESSION OBJECTIVES Define the term nutrition and list the components of the nutrients in the diet. Explain the caloric value of carbohydrates, lipids and proteins. Define the Basal Metabolic rate and calculate the daily energy requirements. Describe the digestion and absorption of carbohydrates, lipids and proteins. Describe the biological value of proteins. Explain the concept of the amino acid pool. Describe the effects of protein energy malnutrition. DEFINITION AND BASIC NUTRITIONAL CONSTITUENTS DEFINITION. Nutrition is the utilization of food stuffs by living organisms. Most of the major biomolecules that are metabolized in the body come from the food that we eat. The body is however able to synthesize some of the biomolecules. ( essential vs non-essential amino acids and fatty acids.) NUTRITIONAL CONSTITUENTS They are 2 major groups of the nutritional constituents that are provided in the diet, namely: MACRONUTRIENTS and MICRONUTRIENTS. MACRONUTRIENTS. i) carbohydrates ii) lipids iii) proteins. Carbohydrates and lipids provide energy. Proteins are for growth and to also replace the tissue in what is called “Turn over of tissue proteins). NUTRITIONAL CONSTITUENTS. MICRONUTRIENTS. i) Vitamins ii) minerals. In additional to the macronutrients and micronutrients, the body also take in water and fiber in the diet. The food stuffs have to be digested before being utilized by the body. Under nutrition and excess consumption leads to MALNUTRITION. Under nutrition is the problem of the developing countries which is associated with diseases such as kwashiorkor, marasmus and diseases due to deficiency of vitamins and minerals. Excess consumption is a problem of the developed countries and causes overweight and obesity leading to cardiovascular diseases, diabetes and some cancers. CALORIC VALUE OF FOOD. Food stuffs produce different amounts of energy which can be measured in the lab in a bomb calorimeter and the unit of energy is calories whose symbol is small c. In biological systems, the unit of energy is Kilo calories( 1000 calories). Below is the amount of energy produced from the various food stuffs: 1. carbohydrates: 4 Kcalories per gram. 2. Proteins: 4 Kcalories per gram. 3. Lipids: 9 Kcalories per gram. Sources of the energy daily requirements: - 45 to 55% comes from carbohydrates. - 25 to 30% comes from lipids. - 15 to 20% comes from proteins TOTAL DAILY ENERGY REQUIREMENTS The total Energy requirements is determined by measuring heat output from the body. It is estimated indirectly from the consumption of oxygen by measuring the respiratory quotient. The respiratory quotient is the ratio of the volume of carbon dioxide produced and the volume of oxygen consumed. Total Daily Energy Requirements is the sum of the Basal Metabolic Rate plus the energy required for physical activity plus the energy required for synthesizing reserves during the fed state called the Specific dynamic action (SDA) BASAL METABOLIC RATE This is the energy output required at rest but not during asleep. It is measured under controlled conditions 12hrs after the last meal. It is the energy required to maintain respiration, circulation, muscle tone, functioning of the visceral such as kidneys, liver and brain. The following are some factors that affect the BMR: - Body weight: BMR increases with weight, the greater the active tissue in a large body the higher th BMR. - Age: BMR reduces with age because the muscle which is active has been replaced by adipose tissue which is metabolically less active. It is higher in children than in adults. - Gender: the BMR is high in males than females because females have more fat which is metabolically less active. ESTIMATION OF TOTAL DAILY ENERGY EXPENDITURE BMR is used to calculate the daily energy requirements. A carpenter of 70Kg weight. 1. 8hrs of carpentry work at 240C/ hr = 1920 2. 8hrs of light work( sedimentary) at 170C/hr = 1260 3. 8hrs sleep at 65C /hr = 520 4. Specific dynamic action = 96 TOTAL 3896 CARBOHYDRATES About 45 to 55 % of the Daily Energy Requirements should come from carbohydrates. A 70Kg man requires about 3000 Kcalories of energy per day and most of it comes from carbohydrates. This is mainly in the form of starch and the disaccharides sucrose and lactose. Cellulose is also an important part of the diet and it provides roughage. Adequate amounts of carbohydrates in the diet have a protein sparing action because it reduces the need to synthesis glucose in gluconeogenesis from the breakdown of proteins. Glycemic index It is measure of the effect of carbohydrates on blood sugar levels. Refined carbohydrates like white bread. Polished rice, breakfast mealie meal have a high Glycemic index(GI) because they are broken down quickly thereby releasing glucose rapidly in circulation. Whole wheat products( brown bread) sweet potatoes have a medium GI. Brown rice roller meal, fruits , vegetables, legumes, nuts have a low GI. They breakdown slowly and release glucose gradually.  Glycemic Index Foods with low GI breakdown slowly and release glucose gradually and they have health beenfits. People that eat food with high GI have an increased risk to developing obesity and are susceptible to the development of diabetes, heart disease and cancer. DIGESTION AND ABSORPTION OF CARBOHYDRATES Digestion of starch starts in the mouth. The food is broken in small particles and it is acted upon by the salivary amylase in the mouth that breaks the alpha type of glycosidic bonds. The pH in the mouth is alkaline. In the stomach the acidic environment with the pH of around 2 stops the action of the salivary amylase. When the food goes down to the duodenum, the carbohydrates are acted upon by the pancreatic amylase produced from the pancreas at a pH of around 8.6. DIGESTION AND ABSORPTION OF CARBOHYDRATES In the jejumun, there are enzymes lactase, sucrase and maltase that breakdown of lactose, sucrose and maltose respectively. Absorption of the monosaccharides in the ileum is through active transportation against the concentration gradient coupled to the sodium and potassium pump. LACTOSE INTOLERANCE. This is due to an inherited disease condition which is prevalent in sub-Saharan Africa. The affected individuals have a deficiency of lactase which manifests after weaning from breast milk. There is failure to digest lactose resulting in abdominal discomfort, diarrhea upon taking milk products. DIGESTION AND ABSORPTION OF LIPIDS The main lipids in the diet are triacyglycerols. Others are phospholipids, cholesterol , cholesterol esters and fat soluble vitamins. The essential fatty acids, the polyunsaturated fatty acids are supplied in the diet through the ingestion of food prepared in vegetable oils. The main enzyme for the digestion of triacyglycerols is the pancreatic lipase in the duodenum. The lipids are emulsified to small droplets ( micelles) by bile salts before being acted upon by the pancreatic lipases. DIGESTION AND ABSORPTION LIPIDS The pancreatic lipases breaks the triacylglycerols into glycerol and fatty acids which are absorbed into the mucosal cells. Once they get into the mucosal cells, the fatty acids and the glycerol re-esterify to triacylglycerols and combine with proteins to form the lipoprotein chylomicrons which is the form in which lipids are transported from the GIT to the liver. DIGESTION AND ABSORPTION OF PROTEINS. The principle function of dietary proteins is for body building. Excess protein in the diet are utilized for the production of energy. Proteins provide 15 to 20% of the Daily Energy requirements. Both quantity and quality of proteins in the diet is important. A. QUANTITY OF PROTEINS. - Adult require about 1gram of protein/Kg body weight per day. DIGESTION AND ABSORPTION OF PROTEINS. B. QUALITY OF PROTEINS. The quality of protein is described as the “ Biological value of proteins” The biological value of proteins is based on the amino acid composition and the digestibility. And based on the biological value , the proteins are divided in 3 groups: i) Proteins of high biological value. ii) Proteins of good biological value. iii) Proteins of poor biological value. DIGESTION AND ABSORPTION OF PROTEINS I) Proteins of high biological value. These contain all the essential amino acids and are easily digestable. They include eggs and milk protein( lactalbumin) ii) Proteins of good biological value. These contain all the essential amino acids but they are not so easily digestable. They include muscle meat, fish, poutry, organ meat and soya beans. DIGESTION AND ABSORPTION OF PROTEINS iii) Proteins of poor biological value. These lack some essential amino acids and are not easily digestable. These are proteins from vegetable sources like cereals and legumes. Proteins in beans lack the essential amino acid methionine while the protein zein in maize lacks the essential amino acid tryptophan. DIGESTION AND ABSORPTION OF PROTEINS Nitrogen balance This a comparison between the intake of nitrogen in the diet and nitrogen that is excreted in the feaces(undigested proteins) and in the urine in the form of urea. i. Nitrogen balance: This is seen in normal healthy adults. The nitrogen they take in is equal to the nitrogen they take out. Nin = Nout. ii. Positive nitrogen balance: This is seen in normal growing children, in pregnant women and in women who are lactating. These are in positive nitrogen balance because the nitrogen they take in is more than the nitrogen they take out. Nin > Nout. iii. Negative nitrogen balance: This is seen in children suffering from protein energy malnutrition and adults suffering from a wasting disease. The nitrogen the take in is less than the nitrogen they take out. Nin< Nout DIGESTION AND ABSORPTION OF PROTEINS. The digestion of proteins starts in the stomach which has an acidic pH of around 2. The acidic pH denatures the protein and makes it susceptible to hydrolysis. In the stomach, the enzyme pepsin is secreted in the form of a zymogen called pepsinogen. The next set of enzymes that are involved in the digestion of proteins are secreted from the pancreas into the duodenum. These are trypsin and chymotrypsin. They are also secreted in the form of the zymogens trypsinogen and chymotrypsinogen respectively. DIGESTION AND ABSORPTION OF PROTEINS In the jejunum, peptidases continue the process of the digestion of proteins in to amino acids. Absorption of the amino acids takes place in the ileum. There are carriers that facilitate the absorption of amino acids which are transported from the GIT to the liver through the portal vein. There are carriers for the following categories of amino acids: a - neutral amino acids, basic amino acids, imino acids, acidic amino acids AMINO ACID POOL Unlike carbohydrates and fats there is no physical storage form of amino acids. There is a continuous break down of old proteins which are replaced by the synthesis of new proteins. The amino acids that are available in the body constitute the Amino acid pool which have got 2 sources: i.)Exogenous from the diet, ii.) Endogenous from the break down of the old body(tissue) proteins. The amino acid in the amino acid pool are utilized for i.) the synthesis of new body proteins, ii) synthesis of nitrogenous compounds e.g. heme, purines and pyrimidines, amines. PROTEIN ENERGY MALNUTRITION This is due undernutrition and is brought about by the deficiency of both proteins and the food that provide the energy: the carbohydrates and lipids. There are 2 forms of forms of PEM namely, marasmus and kwashiorkor. MARASMUS. It is characterized by severe emaciation as a result of prolonged deficiency of carbohydrates, lipids and proteins in the diet. The body fat reserves are depleted and there wastage of muscles. The amino acids from the tissue proteins are used in gluconeogenesis to produce glucose for the RBCs and the brain. PROTEIN ENERGY MALNUTRITION There is reduced synthesis of proteins which results into impaired immune response and an increased risk of infections. There is reduced production of digestive enzymes resulting in the reduction in absorption of nutrients from the GIT. They also manifest signs and symptoms due to deficiency of vitamins and minerals. For example they could develop hypochromic microcytic anemia due to iron deficiency. PROTEIN ENERGY MALNUTRITION KWASHORKOR is due to deficiency of proteins in the diet. This leads to oadema. The children with kwashiorkor also have an impaired immune response, and also have a reduction in in the absorption of nutrients because of impaired cell proliferation of the intestinal mucosa and reduction in the digestive enzymes.