Nutrition I Lecture 2 - PDF

NUTRITION I Nikita Sahadeo, Ph.D. Biochemistry Unit Department of Preclinical Sciences Faculty of Medical Sciences University of the West Indies January 2024 NUTRITION: OVERVIEW Lectures: I Introduction to nutrition and macronutrients II Micronutrients: Vitamins III Micronutrients: Minerals IV Nutri...

NUTRITION I Nikita Sahadeo, Ph.D. Biochemistry Unit Department of Preclinical Sciences Faculty of Medical Sciences University of the West Indies January 2024 NUTRITION: OVERVIEW Lectures: I Introduction to nutrition and macronutrients II Micronutrients: Vitamins III Micronutrients: Minerals IV Nutrition related diseases and assessing nutritional status NUTRITION I: LEARNING OBJECTIVES Describe the components of the diet in terms of macro and micronutrients Explain the term essential nutrients, and outline the biochemical roles of essential nutrients Discuss the concept of recommended daily allowances (RDA) for energy and essential nutrients, the derivation of RDA values, and their limitations Describe the factors that determine energy and protein requirements in man and animals Describe and compare the major contributors to dietary energy intake between man and animals WHAT IS FOOD? Food is anything that is ingested by an organism that is used to: § support its growth; § provide energy; § maintain and repair it. WHAT IS NUTRITION? Process of taking in food and converting it into energy and other vital nutrients required for life Sum of the processes by which an organism utilizes food to sustain its existence Biochemical and physiological process by which an organism uses food to support its life WHAT ARE NUTRIENTS? Any substance used by an organism to survive, grow, and reproduce Required in relatively larger amounts than other nutrients, hence the term “macro” Required in minute quantities (micrograms to milligrams per day), hence the term “micro” MACRONUTRIENTS Provide your body with energy and the components it needs to maintain its structure and functions Carbohydrates, Protein, and Fat Considered essential nutrients: For example, proteins provide essential amino acids, while fats contain essential fatty acids Needed in relatively larger amounts than other nutrients Required in large quantities: 10 grams plus per day Although there are recommended ranges for macronutrient intake, needs vary based on personal circumstances The calorie content of each macronutrient is: 4 calories/g 4 calories/g 9 calories/g ENERGY REQUIREMENTS Energy is required in the body for metabolic processes, physiological functions, muscular activity, heat production, growth and synthesis of new tissues. Released from food components by oxidation. Main sources are carbohydrates, proteins, fats and, to a lesser degree, alcohol. Average amount of energy released ranges from approximately 16.7 kJ/g for carbohydrates or protein to 29.3 kJ/g for alcohol and 37.7 kJ/g for fats. ESTIMATING ENERGY REQUIREMENTS Distribution of energy requirements of a population group or class of individuals* * It is assumed that individual requirements are randomly distributed about the mean requirement for the class of individuals, and that the distribution is Gaussian. Source. WHO, 1985. ESTIMATING ENERGY REQUIREMENTS Probability that a particular energy intake is inadequate or excessive for an individual* * Individuals are randomly selected among a class of people or a population group. The two probability curves overlap, so the level of energy intake that assures a low probability of dietary energy deficiency is the same level that implies a high probability of obesity owing to dietary energy excess. Source: WHO, 1985. DAILY ENERGY REQUIREMENTS Recommendations for energy intake differ from those for nutrient intake in that: § They are not increased to cover the needs of most members of the group or population, as this level of intake would lead to overweight or obesity in most people. § There are differences between the actual energy requirements needed to maintain current body size and level of physical activity and the desirable energy requirements needed to maintain body size and levels of physical activity consistent with good health. § They can be applied cautiously to individuals, using estimates of energy expenditure. However, predictive estimates are much less accurate for individuals than for groups, and variations in energy expenditure can be large, even between apparently similar individuals. § There is wide inter-individual variation in the behavioural, physiologic and metabolic components of energy needs. The average energy intake recommended for a defined group cannot be applied to other groups or individuals who differ from the defined group average in gender, age, body size, activity level and possibly other factors. 2 EER TERMS Two separate terms can therefore be used to express and determine Estimated Energy Requirements (EER): § The Estimated Energy Requirement for Maintenance (EERM, or actual energy requirement) is the dietary energy intake that is predicted to maintain energy balance (plus extra needs for pregnancy, lactation and growth) in healthy individuals or groups of individuals at current levels of body size and level of physical activity. § The Desirable Estimated Energy Requirement (DEER, or energy reference value) is the dietary energy intake that is predicted to maintain energy balance (plus extra needs for pregnancy, lactation and growth) in healthy individuals or groups of individuals of a defined gender, age, weight, height and level of physical activity consistent with good health and/or development. PERSONAL ENERGY REQUIREMENT personal energy requirement = basic energy requirement + extra energy requirement Basic ER = 1.3 calories x hours x kg body weight Extra ER = 8.5 calories x hours x kg body weight Example: For a 60 kg person (132 lbs) who exercises for 2 hr every day: = (1.3 x 24 x 60) + (8.5 x 2 x 60) = 1872 + 1020 = 2892 calories FUNCTIONS OF CARBOHYDRATES Energy Production Energy Storage Building Macromolecules Sparing Protein Lipid Metabolism COMPLEX VS. SIMPLE CARBOHYDRATES Simple carbohydrates are monosaccharides and disaccharides Complex carbohydrates are polysaccharides such as starch Simple carbohydrates are quickly digested and absorbed by the body whereas complex carbohydrates take time to be digested GLUCOSE Glucose is a simple sugar with the molecular formula C₆H₁₂O₆ Glucose is the most abundant monosaccharide The principal fuel used by the brain and nervous system and by red blood cells Carbohydrates are broken down into glucose FRUCTOSE Absorbed almost entirely by the liver as most cells lack its transporter glut-5 Does not stimulate insulin release Poorly absorbed from gastrointestinal tract: § peripheral blood concentration ≈0.01 mmol/L vs. glucose 5.5 mmol/L Does not suppress grehlin Predominantly absorbed passively from the intestinal lumen via the hexose transporter SLC2A5, also known as GLUT5, which has high affinity for fructose (Km = 6 mM). Fructose is a poor substrate for the hepatic hexokinase glucokinase (GCK). Instead, ketohexokinase (KHK, also known as fructokinase) rapidly phosphorylates fructose to generate fructose-1-phosphate (F1P). KHK’s high activity and insensitivity to cellular energy status account for the liver’s ability to efficiently extract fructose. F1P is metabolized to dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3phosphate (G3P), which enter the glycolytic/gluconeogenic metabolite pools doi: 10.1172/JCI96702 MORE ON FRUCTOSE Cellular metabolic status and energy status tightly regulate the phosphofructokinase (PFK) step in glycolysis, which limits hepatic glycolytic flux. In contrast, fructose-derived metabolites enter the triose-phosphate pool distal to PFK and therefore bypass this restriction. As hepatic fructolysis is unrestricted, fructose loads can lead to large, rapid expansions in the hexose- and triose-phosphate pools, potentially providing increased substrate for all central carbon metabolic pathways, including glycolysis, glycogenesis, gluconeogenesis, lipogenesis, and oxidative phosphorylation. doi: 10.1172/JCI96702 GLYCEMIC INDEX (GI) A measure of the potency of a test food at raising blood glucose level compared to potency of glucose Ranks the glycemic potency of foods Calculated as the incremental area under the curve (iAUC) for blood glucose after consumption of a test food divided by the iAUC of a reference food containing the same amount of carbohydrate Calculated as the incremental area under the curve (iAUC) for blood glucose after consumption of a test food divided by the iAUC of a reference food containing the same amount of carbohydrate Example of calculation of GI for white bread: § subject fed 50g of glucose (i.e. 50g carbohydrate) § blood glucose level after 2 hrs is 180 mg/dl § subject fed 71g of bread (i.e. 50g carbohydrate) § blood glucose level after 2 hrs is 126 mg/dl § GI = 100 x (126 / 180) = 70 GLYCEMIC LOAD Refers to the amount of carbohydrate consumed multiplied by the rate at which the carbohydrate is metabolized and enters the bloodstream (glycemic index) Takes size of portions into account Indicates how much a given serving of a test food will raise blood glucose GL = (GI / 100) x g of carbohydrate in serving Example: § GI of watermelon is 72 § Given 120g of watermelon has 6g of carbohydrate: § GL of this = (72/100) x 6 = 4.32 § Thus 120g watermelon has a low glycemic load 41 FUNCTIONS OF PROTEINS Growth and Maintenance Causes Biochemical Reactions Acts as a Messenger Provides Structure Maintains Proper pH Balances Fluids Transports and Stores Nutrients Provides Energy ESSENTIAL AMINO ACIDS FATS & OIL S ESSENTIAL FATTY ACIDS https://www.who.int/news-room/fact-sheets/detail/healthy-diet https://www.fao.org/3/y5686e/y5686e04.htm Human energy requirements Report of a Joint FAO/WHO/UNU Expert Consultation Rome, 17-24 October 2001 UNITED NATIONS UNIVERSITY WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 2004