Principles of Nutrition PDF

Principles of Nutrition Year 2 – Unit I, Problem #1 Mai Sater, MD PhD Department of Medical Biochemistry Academic Year 2024- 2025  Nutrition Nutrients: are the constituents of food needed to sustain the normal body...

Principles of Nutrition Year 2 – Unit I, Problem #1 Mai Sater, MD PhD Department of Medical Biochemistry Academic Year 2024- 2025  Nutrition Nutrients: are the constituents of food needed to sustain the normal body functions. Nutrients: Macronutrients: Fats, proteins, carbohydrates Micronutrients: minerals and vitamins Nutrients provide: Energy Essential molecules which: Cannot be synthesized by the body (hence essential) or, Can not be synthesized at a rate sufficient to meet the needs for growth and maintenance.  Essential Nutrients Proteins/Amino Acids Fatty acids Carbohydrates Vitamins: Loading… Both water- and fat-soluble vitamins Minerals: Including: calcium, phosphorous, sodium, potassium, and iron.  Dietary Reference Intakes (DRI) DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and gender the Food and Nutrition Board of the Institute of Medicine and the National Academy of Sciences have compiled Dietary Reference Intake (DRI) DRI is an estimate of the amount of nutrients required to prevent deficiencies and maintain optimal health and growth Dietary Reference Intake values include: 1. EAR: Estimated Average Requirement 2. RDA: Recommended Dietary allowance 3. AI: Adequate Intake 4. UL: Tolerable Upper Intake Level  Dietary Reference Intakes (DRI) EAR: Estimated Average Requirement The average daily nutrient intake level estimated to meet the requirement of one half (50%) of healthy individuals in a particular stage and gender group. It is useful in estimating the actual requirements in groups and individuals. RDA: Recommended Dietary allowance Loading… An estimate of the amount of a nutrient needed to meet the needs of nearly all (97- 98%) of individuals in a life stage and gender group. RDA = EAR + 2SDEAR AI: Adequate Intake Used when sufficient evidence is not available to calculate EAR or RDI. It is based on estimation of nutrient intake by a group of apparently healthy people. UL: Tolerable Upper Intake Level The highest average daily nutrient intake level that is likely that is likely to pose no risk of adverse health effects to almost all individuals in the general population  Energy requirements in Humans The Estimated Energy Requirement (EER) is by definition: the average dietary energy intake predicted to maintain an energy balance (the calories consumed=energy expended) in a healthy adult of a defined age, gender, height and physical activity. Recommended energy intake: Varies based on genetics, body composition, metabolism, and behavior of individual. Some approximations can provide simple estimates, for example: Sedentary adult requires 30 kcal/kg/day Moderately active adult requires 35 kcal/kg/day Active adults require 40 kcal/kg/day  Energy Content of Food This is calculated from the heat generated by the total combustion of food in a calorimeter, and is expressed in kcal, or Cal). Energy content of fat is more than twice that of protein or carbohydrate. Energy content of ethanol is intermediate between fat and carbohydrate. Average energy available from the major food components  Use of Food Energy in the Body The energy generated by metabolism of the macronutrients (fats, proteins, carbohydrates) is used for three energy-requiring processes that require in the body, which are: Basal Metabolic Rate (BMR): It represents the energy required to carry out the normal body functions such as respiration, blood flow and ion transport. Physical Activity: Provides the greatest variation in energy requirements: the amount of energy consumed depends on the duration and intensity of the exercise. Thermic Effect of Food (diet induced thermogenesis) increased production of heat by 30% during food digestion and absorption. Neupane et al., 2019  Dietary Fats Triacylglycerol (TAG) constitute the majority (90%) of dietary lipids. The influence of TAG on blood lipids is determined by the chemical nature of their constituent fatty acids. Fats: Saturated fats (absent double bonds) Monounsaturated fats (MUFA) (single double bond) Polyunsaturated fats (PUFA) (at least two double bonds) Trans fats  Dietary Fats Saturated fats TAGs composed of fatty acids whose hydrocarbon chain does not contain any double bond. Consumption associated with increase levels of LDL-C and heart disease Found in: meats, dairy, some oils like coconut and palm oils. Monounsaturated fats (MUFA) TAGs contain fatty acids with one double bond Loading… Consumption lowers both total cholesterol and LDL-C, and maintains (or increases) HDL-C Found in: fish and vegetable oils Polyunsaturated fats (PUFA) TAGs with fatty acids containing more than one double bond Effect on cardiovascular health depends on the location of the double bond (omega-3, omega-6) Trans fats Chemically classified as unsaturated, but behave like saturated. They increase LDL-C, with no effect on HDL-C, and overall increase cardiovascular disease. Composition of commonly encountered dietary fats  Dietary Carbohydrates Monosaccharides: The principal monosaccharides are: Glucose (fruits, sweet corn, corn syrup and honey) Fructose (honey and fruits). Galactose (dairy products) Disaccharides: The most abundant disaccharides are sucrose, lactose and maltose. Polysaccharides: Complex sugars, including starch found in plants, wheat, and vegetables. Dietary fiber: Non-digestible carbohydrates (cellulose, lignin and pectin). Increases the bowel motility, and thus reduces the exposure to carcinogens, and thus the risk of cancer, constipation, and hemorrhoids.  Dietary Proteins Provide essential amino acids for protein synthesis. Sources: Animal: contain all essential amino acids. Plants: do not contain all essential amino acids, thus have lower biologic value than animal proteins. Healthy adults have a normal nitrogen balance, which occurs when the amount of nitrogen consumed equals that of excreted nitrogen (urine, sweat, feces).  Nitrogen Balance Nitrogen Balance: Difference between nitrogen consumed and excreted nitrogen Positive Nitrogen Balance: Consumed nitrogen exceeds excreted nitrogen. Typically seen in : Children & pregnancy Recovery from a severe illness, Some pathological conditions, such as tissue growth. Negative Nitrogen Balance: Excreted nitrogen exceeds consumed nitrogen. Associated with: Inadequate dietary protein intake, Lack of an essential amino acid Physiologic stresses: trauma, burns, illness or surgery.  Dietary Minerals & Vitamins Minerals: dietary minerals come directly from plants, or indirectly from animal sources. Minerals are also present in drinking water in variable proportions depending on the geographical location. Vitamins: they are organic compounds that cannot be synthesized in adequate quantities by humans, and must be supplied by the diet. Water soluble (B complex, and Vit C): readily excreted by the kidneys, hence toxicity is rare. Fat-soluble (A, D, E, K): Not readily excreted and may be stored in adipose tissue and liver causing toxicity.