Fuel Homeostasis Energy Content of Foods and Energy Requirements Content created and narrated by: Jiyan Ma PhD Molecular and Cellular Biochemistry For more information contact: Charles E. Bell PhD Associate Professor, Dept. of Molecular and Cellular Biochemistry

Primary Learning Objective Secondary Learning Objective Define calorie, respiratory quotient, and daily energy expenditure, and describe how these values are measured or calculated Define and differentiate direct and indirect calorimetry; identify the reasons why a direct calorimetry may give different values than animal or human calorimetry Define basal metabolic rate (BMR), thermic effect of food (also called Diet-induced thermogenesis, DIT), daily energy expenditure, and described how these values are measured or calculated Integrate the metabolic pathways leading to ATP production to those involving biosynthetic pathways leading amino acid, lipids, nucleic acids and correlate with their changes in diseases

1.Units Used to Measure Energy 2.Energy Content of Food — 2.1 Direct Calorimetry — 2.2 Indirect Calorimetry — 2.3 Respiratory Quotient (RQ) — 2.4 Energy Density 3. Energy Needs of Human Body — 3.1 Basal metabolism — 3.2 Physical activities — 3.3 Thermic effect of food — 3.4 Calculating daily energy expenditure Content

1. Units Used to Measure Energy 1000 calorie = 1 kilocalorie (kcal) = 1 Calorie = 4180 joules = 4.18 kilojoules (kj)

2. Energy content of food 2.1 Direct Calorimetry CHO + O 2 CO 2 + H 2 O Heat e.g. Question: Is the energy content determined by direct calorimetry the same as that measured inside the body?

2.2 Indirect Calorimetry Indirect calorimetry estimates caloric yield in the body by measuring the oxygen consumed, carbon dioxide produced, and nitrogen eliminated. CarbohydratesFatsProteins Energy content (kcal/g) Direct calorimetry Metabolic (average) O 2 consumed (L/g) CO 2 produced (L/g) kcal/ O 2 consumed (L) Kcal/CO 2 produced (L)

2.3 Respiratory Quotient (RQ) Respiratory quotient (RQ) is defined as the ratio of the volume of CO 2 produced (exhaled) to that of O2 utilized (inhaled) in the process of metabolism of a substance. RQ for Major Fuels Carbohydrate1 Protein0.8 Fat0.7 RQ is used to determine the energy contribution from one type of nutrient in a mixed diet.

Fuel usage in a Marathon runner In this study, a well-fed runner ran for 25 minutes at a given rate, stopped for 5 minutes so tests could be run, then continued with the next rate for 25 minutes and so on for a total of six hours. All the results are given at the table below. Protein metabolism accounted for only 2% of the total energy production and has been neglected. (Edwards, et al., Am. J. Physiol. 108:203 (1934)) Running Rate Body Weight Blood Sugar O 2 Use RQTotal From CHO From Fats Fraction From Fat GlycogenFats km/hrkgMmmoles gg Total ~P Energy ProductionWt. of FuelsMeasurements

~ 10 minutesGlycogen ~ minutes Glycogen > 20 minutes Glycogen Fatty acid > 2 hour Vigorous activity (>75% VO 2max ) Glycogen depletion “hitting the wall” Continue for a short time Fatty acid GluconeogenesisBlood glucose Halt CNS functionIf continue…hypoglycemia DurationFuel types Fuel Consumption During Exercise

2.4 Energy Density Energy Density (or calorie-density) is the number of calories per gram of a food item. Higher energy density kcal/g Taco shell 4.7 Bologna3.1 Fried chicken2.8 Fried pork chop2.8 Cheseburger2.7 Hash brown potato2.2 Fried fish2.2 Fried rice1.6 Potato salad1.4 Sweetened Strawberries1.1 (frozen) Low energy density kcal/g Corn tortilla 2.2 Sliced turkey breast0.9 Grilled chicken1.7 Broiled pork chop2.0 Bean burrito1.9 Broiled potato0.9 Broiled fish1.2 Rice1.3 Tossed salad (with dressing)1.1 Fresh Strawberries0.3

Summary for Energy Content of Food The units used to measure energy in Nutrition include calorie, kilocalorie (kcal) and Calorie. Direct calorimetry determines the total energy content of a food by measuring heat released from total physical combustion of a food. Indirect calorimetry estimates caloric yield in the body by measuring oxygen consumed, carbon dioxide produced, and nitrogen eliminated. Respiratory quotient is the ratio of the volume of CO 2 produced to that of O 2 utilized, which is used to determine the energy contribution from one type of nutrient in a mixed diet. Energy density is the number of calories per gram of a food item.

3. Energy Needs of Human Body The body expends energy to maintain physiological functions, support physical activity and process food. Collectively, these components of energy use make up total energy expenditure (TEE).

3.1 Basal Metabolism Basal metabolism is the energy expended to sustain basic, involuntary life function such as respiration, beating of the heart, nerve function, etc. Basal Metabolic Rate (BMR) is the most commonly used measure for basal metabolism. It is measured right after awakening using indirect calorimetry and requires the testing subject to be: awake (it is 10% less if asleep) lying quietly in a room at neutral warm temperature in a postabsorptive state (fasting overnight) free from strong emotions

3.2 Physical activities 3.3 Thermic effect of food fats ~5% carbohydrate ~10% protein ~20-30% Mixed diet~10%

3.4 Calculating daily energy needs 1.Determine BMR and calculate daily (24 hours) energy requirement for basal metabolism 2.Correct for the 10% decrease in metabolic rate during sleep 3.Determine the energy requirements for daily physical activity (using the table provided on handout). The values are low because they do not include BMR and they represent an averaging over a long period of time (waking hours) 4.Correct for thermogenesis (10% for mixed diet) 5.Add all together and that is the daily energy needs

Summary for Energy Needs of Human Body The total energy expenditure of human body consists of three major parts, which are basal metabolism (~ %), physical activities (~ %), and thermic effect of food (~10%). Basal metabolism is the energy expended to sustain basic involuntary function, and BMR (Basal Metabolic Rate) is the most common measure to determine the basal metabolism. BMR is influenced by many factors, and in adults, BMR is most closely related to lean body mass. Physical activities account for ~ % of total energy expenditure in the body. Thermic effect of food is the extra heat produced when food is ingested, which is estimated as 10% of a mixed diet.

A brief review of terms Kilocalorie (kcal) A commonly used energy measuring unit, which equals to the energy required to raise the temperature of 1 kg of water for 1 degree centigrade. 1 kcal = 1000 calorie = 1 Calorie = 4180 joules = 4.18 kilojoules (kj) Direct calorimetry A measurement of energy content of food, which meausres the heat released from total physical combustion of food. Indirect calorimetry A measurement of energy expenditure obtained by assessing nitrogen excretion, oxygen consumption and carbon dioxide production. Respiratory Quotient (RQ) A measurement used to assess the energy contribution from different types of nutrients. It is defined as the ratio of the volume of CO 2 produced to that of O 2 utilized in the process of metabolism of a substance. Total energy expenditure (TEE) Total energy expended by the body. It can be divided into three parts: basal metabolism (50-70%), physical activities (15-30%), thermic effect of food (10%). Basal metabolism Energy expended to sustain activities related to basic vital body functions. Basal metabolic rate (BMR) Energy expended for basal metabolism per hour, which is closely related to lean body mass. Thermic effect of food (also called thermogenesis, diet induced thermogenesis (DIT)) Energy expended for the digestion, absorption, and metabolism of nutrients. Energy density (caloric density) Energy per amount of a food item. Resting metabolic rate (BMR) A measure of energy expenditure assessed under less striingent conditions than is BMR.

Thank you for completing this module I can answer any questions you may have: Charles Bell PhD

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