NUTRITION / BMR / SDA

NUTRITION / BMR / SDA

1. Nutrition Gandham.Rajeev Email:[email protected]

2. Introduction Nutrition is the science of nourishing the body. Nutrition may be defined as utilization of food by living organisms. Food is the fuel source of the body. The ingested food undergoes metabolism to liberate energy required for growth, maintenance of tissues of body & regulation of body process.

3. Classification Based on chemical nature, nutrients are classified into six classes : Carbohydrates Lipids Proteins Minerals Vitamins Water

4. Based on biological role: Nutrients are classified into energy providing nutrients & protective nutrients Energy providing nutrients: Carbohydrates & lipids Protective nutrients: Proteins, minerals, vitamins & water. Based on daily requirement: Classified into macronutrients & micronutrients

5. Caloric value of foods Calorie: A physiological calorie ( kilocalorie ) is defined as the amount of heat required to raise the temperature of one kilogram of water by one degree centigrade. Determination of caloric value of foods: By using the bomb-calorimeter.

6. Bomb-calorimeter is a metal vessel in which the weighed food is ignited in an atmosphere of oxygen under pressure by electric spark. A measured volume of water surrounds the vessel. When the temperature is multiplied by the volume of water surrounding the vessel, the total number of calories liberated by the combustion of the food is obtained.

7. Bomb-Calorimeter

8. Gross caloric values: By using bomb-calorimeter 1gm of carbohydrates yields 4.1 calories 1gm of fat yields 9.4 calories 1gm of proteins yields 5.4 calories

9. Digestible caloric values: Digestible caloric value of foods are 1gm of carbohydrates = 4.0 calories, 1gm of fat = 9.0 calories 1gm of proteins = 5.2 calories. Note: Proteins are not completely oxidized in the body.

10. T he end product is urea , it contains some amount of potential energy (1.25 calories/ gm ) The oxidizable caloricfic value of protein =4.0 Actual caloric values: 1gm of carbohydrates = 4 calories, 1gm of fat = 9 calories 1gm of proteins = 4 calories. Ethanol = 7 calories.

11. Respiratory Quotient (RQ) The respiratory quotient (RQ) is the ratio of the volume of CO2 produced to the volume of O2 utilized in the oxidation of foodstuffs. Volume of CO2 produced Volume of O2 used RQ =

12. Determination of RQ Done by open circuit method The subjects breaths in the atmospheric air of known composition. The expired air is collected in a rubber bag or spirometer . The volume of expired air, the O2 content & CO2 content are measured. RQ is calculated by using the formula.

13. Respiratory Quotient Carbohydrates: The carbohydrates are completely oxidized. R.Q .for carbohydrate = 1 Fats: Fats have relatively lower R.Q. They have a low oxygen content. Fats require more O 2 for oxidation. R.Q. for the oxidation of the fat = 0.7

14. Proteins: The chemical nature of proteins is highly variable The R.Q. of protein is 0.8 Mixed diet: R. Q. of the diet consumed is dependent of the relative composition of carbohydrates, fats and proteins. For a normal diet, it is around 0.8.

15. Utilization of energy Three process to meet fuel demand of the body……. Basal metabolic rate (BMR) Specific dynamic action (SDA) Physical activity.

16. Basal metabolic rate (BMR) BMR is defined as the minimum amount of energy required by the body to maintain life at complete physical and mental rest in the post-absorptive state (i.e. 12 hours after the last meal). It may be noted that resting metabolic rate (RMR) is in recent use for BMR.

17. Several functions within the body continuously occur. These include working of heart & other organs, Respiration, Blood circulation, Conduction of nerve impulse, Reabsorption by renal tubules, Gastrointestinal motility & ion transport across membranes, Na + -K + pump, Synthesis of macromolecules.

18. Measurement of BMR Prerequisite conditions: Post-absorptive state Mental & physical relaxation Person is awake Temperature maintained at 20-25°C Supine position.

19. Measurement: The BMR is determined either by the apparatus of Benedict & Roth (closed circuit device) or by the Douglas bag method (open circuit device). By Benedict-Roth method, the volume of O2 consumed (recorded on a graph paper) by the subject for a period of 2-6 minutes under basal conditions is determined.

20. Calculation of energy consumption The energy consumed is calculated from oxygen consumption. The oxygen consumed per hour is multiplied by constant 4.825 calories. One liter of oxygen consumption is equivalent to 4.825 calories, when RQ of diet is 0.82.

21. For the calculation of body surface area, the simple formula by Du Bois and Du Bois is used. Body surface area = A = H 0.725 x W 0.425 x 71.84 A = Surface area in cm 2 H = Height in cm W = Weight in kg. H 0.725 x W 0.425 x 71.84

22. Benedict & Roth Instrument

23. Normal values BMR is expressed as cal/ sq.m /hr Adult males: 38 cal/ sqm /hr Adult females: 33 cal/ sqm /hr The average body surface area for Indian males is 1.62 sqm For females = 1.4 sqm

24. Factors affecting BMR Surface area: BMR is directly proportional to surface area. Surface area is related to weight & height. Sex: Men have higher (about 5%) BMR than women. Due to the higher proportion of lean muscle mass in men. Age: In infants & growing children, with lean muscle mass, the BMR is higher.

25. In adults, BMR decreases at the rate of about 2o% per decade of life. Physical activity: BMR is increased in persons (athletes) with regular exercise. Due to increase in body surface area. Hormones: Thyroid hormones (T3 & T4) have a stimulatory effect on the metabolism of the body & BMR.

26. Epinephrine, cortisol, growth hormone & sex hormones increase BMR. Environment: In cold climates, the BMR is higher compared to warm climates. Starvation: During the periods of starvation, the energy intake has an inverse relation with BMR, a decrease up to 50%

27. Fever: Fever causes an increase in BMR. An elevation by more than 10% in BMR is observed for every 1°C rise in body temperature. Disease states: BMR is elevated in various infections, leukemias , polycythemia, cardiac failure, HTN. In Addison's disease BMR is lowered.

28. Significance of BMR BMR is important to calculate the calorie requirement of an individual & planning of diets. Determination of BMR is useful for the assessment of thyroid disorders. BMR is increased in thyrotoxicosis (hyperthyroidism). BMR is decreased in hypothyroidism.

29. Specific dynamic action (SDA) The phenomenon of the extra heat production by the body, over and above the calculated caloric value, when a given food is metabolized by the body, is known as specific dynamic action (SDA). It is also known as calorigenic action or thermogenic action or thermic action (effect) of food.

30. SDA for different foods SDA for different foods: For a food containing 25 g of protein, the heat production from the caloric value is 100 Cal (25 x 4 Cal). When 25 g protein is utilized by the body, 130 Cal of heat is liberated. The extra 30 Cal is the SDA of protein.

31. SDA for protein, fat and carbohydrate 32%, 13% & 5%, Proteins possess the highest SDA while carbohydrates have the lowest. SDA for mixed diet: The presence of fats & carbohydrates reduces the SDA of proteins. Fats are most efficient in reducing SDA of foodstuffs. For a regularly consumed mixed diet, the SDA is around 10%

32. Significance of SDA For the utilization of foods by the body, certain amount of energy is consumed from the body stores. Expenditure by the body for the utilization of foodstuffs. It is the highest for proteins (30%) & lowest for carbohydrates (5%) & for mixed diet 10%

33. Additional 10% calories should be added to the total energy needs (of the body) towards SDA. The higher SDA for protein indicates that it is not a good source of energy

34. Mechanism of SDA SDA of foods is due to the energy required for digestion, absorption, transport, metabolism and storage of foods in the body. The SDA of proteins is primarily to meet the energy requirements for deamination, synthesis of urea, biosynthesis of proteins, synthesis of triacylglycerol (from carbon skeleton of amino acids).

35. Phenylalanine, glycine and alanine increase the SDA. The SDA of carbohydrates is attributed to the energy expenditure for the conversion of glucose to glycogen. Fat, the SDA may be due to its storage, mobilization and oxidation.

36. Consumption of protein rich diet cold climates: In cold climates, diet rich in proteins is recommended, it helps to maintain the body temperature. Due to its high SDA, liberates extra heat.

37. Physical activity The energy requirement depend on the occupation, physical activity and lifestyle of the individual. Light worker (teachers, doctors) 30-40%BMR Moderate worker (housewives, students) 40-50% BMR Heavy work ( labourers ) 50-60% BMR Very heavy work (workers & rickshaw pullers) 60-100% BMR

38. Energy requirement of man Individual with light work about 60% of the calories are spent towards BMR, about 30% for physical activity & about 10% to take care of the SDA. Light work 2,200 – 2,500 Cal/day Moderate work 2,500 – 2,900 Cal/day Heavy work 2,900 – 3,500 Cal/day Very heavy work 3,500 – 4,000 Cal/day

39. Environmental temperature Low temperature increases energy expenditure by inducing shivering & nonshivering thermogenesis Shivering provides heat by increasing muscle activity in response to cold stress. Nonshivering thermogenesis also produce heat. It is due to brown adipose tissue. It is stimulated by epinephrine & norepinephrine .

40. Questions Define BMR. How it is determined? Describe the factors affecting the BMR. Mention the significance of BMR. Define SDA. Mention the SDA for proteins, fats and carbohydrates. Mention its significance. Define RQ. Mention the significance of RQ.

41. Reference books Medical Biochemistry - AR Aroor Text book of Biochemistry - U.Satyanarayana Biochemistry – Pankaja Naik Text book of Biochemistry – DM Vasudevan