UNIT-IV NUTRITION: Nutrition (also called nourishment or aliment) is the provision, to cells and organisms, of the materials necessary (in the form of food) to support life. Many common health problems can be prevented or alleviated with a healthy diet Food energy is the amount of energy obtained from food that is available through cellular respiration.
ENERGY CONTENT OF FOOD Food energy is expressed in food calories (EU kcal, US/Canada Calories) or kilojoules (kJ). Food calories, or the "Calorie" units used often in nutritional contexts, measure amounts of energy 1000 times greater than the units in scientific contexts known also as calories, or gram calories ("cal"). Food calories are thereby referred to less ambiguously in some formal contexts as kilocalories (kcal) or kilogram calories. One food calorie is equal to 4.184 kilojoules Respiratory quotient of food stuffs
The respiratory quotient (R.Q) is the ratio of the volume of co2 produced to the volume of O2 Carbohydrates: The carbohydrates are completely oxidized and their R.Q is close to 1
C6H12O6 + 6O2Æ 6CO2 + 6H2O
R.Q for carbohydrates = co2/co2 = 6/6= 1 Fats Fats have relatively low R.Q since they have a low oxygen content. For
this reason, fats require more O2 for oxidation 2C57H110O6 + 163O2 --> 114CO2 + 110 H2O
R.Q of fat = CO2/CO2= 114/163 = 0.7 Proteins The chemical nature of proteins is highly variable and this cannot be represented by any specific formula. By indirect measurements, the R.Q of protiens is found to be 0.8 Mixed diet The R.Q of the diet consumed is dependent of the relative composition of carohydrates, fats & protiens. For a normally indigested diet, it is around 0.8 Utilization of energy in man BMR (Basal metabolic rate) Definition: Basal Metabolic Rate (BMR) is the number of calories your body burns at rest to maintain normal body functions. It is the amount of calories per day your body burns, regardless of exercise. It changes with age, weight, height, gender, diet and exercise habits. Measurement of BMR: Preparation of the subject : the subject should be awake at complete physical and mental rest in a post absorptive state and ina comfortable surrounding at 25C.
Measurement of BMR: The BMR is determined either by the apparatus of Benedict’s and Roth or by the douglas bag method. Units of BMR: BMR is expressed as calories per square metre of body surface area per hour such that Cal/sq.m/hr. • BMR Calculation for Women: 655 + (4.35 × weight in pounds) + (4.7 × height in inches) – (4.7 × age in years)
• BMR Calculation for Men: 66 + (6.23 × weight in pounds) + (12.7 × height in inches) – (6.76 × age in years). Factors affecting BMR: • Surface area • Sex • Age • Physical activity • Hormones • Environment • Starvation • Fever • Disease state • Racial variation • Significance of BMR: • BMR is important to calculate the calorie requirement of an individual and planning of diets. • Specific dynamic action (SDA) • The effect of ingestion and assimilation of food and especially of protein in increasing the production of heat in body. SDA for different foods: For a food containing 25gm of protein they heat production from the caloric value is 100cal(25x4 cal). However when 25gm protein is utilized by the body, 130cal of heat is liberated the extra 30cal is SDA of protein. SDA for protein, fat and carbohydrate or 30%, 13%,5% repectively. Significance of SDA: The higher SDA for protein indicates that it is not a good source of energy fat is the best source of energy due to its lowering effect on SDA. PHYSICAL ACTIVITY OF THE BODY: The physical activity of the individual is highly variable. The amount of energy needed for this depends mainly on the duration and intensity of muscular activity. The individuals are grouped into four categories with regard to their physical activity and the requirement of energy. Light work -- 30-40% of BMR (teachers, office workers, doctors) Moderate work -- 40-50% of BMR (housewives, students) Heavy work -- 50-60% of BMR (agricultural labrourers, miners) Very Heavy work -- 60-100% of BMR (construction workers, riksha pullers) NUTRITIONAL IMPORTANCE OF CARBOHYDATES: Carbohydrates are the most abundant dietry constituents, despite the fact that they are not essential nutrients to the body. From the nutritional point of view , carbohydrates are grouped into two categories: 1.carbohydrate utilized by the body- starch, glycogen, sucrose, lactose, glucose and fructose. 2.carbohydrates not utilized by the body- cellulose, hemicelluloses, pectin.
Functions of carbohydrates: • Major sources of energy. • protein sparing action: • absolute requirement by brain • required for the oxidation of fat • energy supplied for the muscle work • synthesis of pentoses • synthesis of non-essential amino acids • synthesis of fat