Fuel HomeostasisEnergy 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 PhDAssociate 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

CalorimetryCHO + O2 CO2 + H2O

Heat

e.g.

Question:Is the energy content determined by direct calorimetry the same as that measured inside the body?

2.2 Indirect CalorimetryIndirect calorimetry estimates caloric yield in the body by measuring the oxygen consumed, carbon dioxide produced, and nitrogen eliminated.

Carbohydrates Fats Proteins

Energy content (kcal/g)

Direct calorimetry 3.7-4.3 9.5 4.0-4.3

Metabolic (average) 4.1 9.3 4.1

O2 consumed (L/g) 0.75-0.83 2.03 0.97

CO2 produced (L/g) 0.75-0.83 1.43 0.78

kcal/ O2 consumed (L) 5.0 4.7 4.5

Kcal/CO2 produced (L) 5.0 6.6 5.6

2.3 Respiratory Quotient (RQ)Respiratory quotient (RQ) is defined as the ratio of the volume of CO2 produced (exhaled) to that of O2 utilized (inhaled) in the process of metabolism of a substance.

RQ for Major FuelsCarbohydrate 1Protein 0.8Fat 0.7

RQ is used to determine the energy contribution from one type of nutrient in a mixed diet.

Fuel usage in a Marathon runnerIn 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))

RunningRate

BodyWeight

BloodSugar

O2

UseRQ Total From

CHOFrom Fats

FractionFrom Fat

Glycogen Fats

km/hr kg Mm moles moles moles moles g g0 59.61 5.6

11.3 59.32 4.6 2.75 0.97 17.1 15.5 1.6 0.09 67 39.3 59.03 4.9 2.34 0.96 14.5 12.7 1.8 0.12 55 4

11.3 58.82 4.8 2.71 0.94 16.6 13.5 3.1 0.19 58 69.3 58.65 4.4 2.31 0.88 13.8 8.5 5.3 0.38 37 11

11.3 58.25 4.6 2.76 0.86 16.5 9.0 7.5 0.45 39 159.3 58.15 4.5 2.40 0.82 14.1 5.7 8.4 0.60 25 16

11.3 57.93 4.2 2.85 0.82 16.7 6.8 9.9 0.59 29 199.3 57.78 4.3 2.44 0.79 14.1 4.2 9.9 0.70 18 20

11.3 57.48 3.8 2.85 0.82 16.7 6.8 9.9 0.59 29 199.3 57.30 4.1 2.49 0.79 14.3 4.3 10.0 0.70 19 20

11.3 57.55 3.7 2.88 0.81 16.9 6.3 10.6 0.63 27 219.3 57.35 3.2 2.48 0.77 14.3 3.2 11.0 0.77 14 22

Total 185.5 96.5 89.0 415 175

~P Energy Production Wt. of FuelsMeasurements

~ 10 minutes Glycogen

Glycogen~ 10 -20 minutes Glycogen

> 20 minutes GlycogenGlycogen Fatty acid

Fatty acid> 2 hour Vigorous activity (>75% VO2max)

Glycogen depletion

“hitting the wall”

Continue for a short timeFatty acid

Gluconeogenesis Blood glucose

Halt CNS functionIf continue… hypoglycemia

Duration Fuel types

Fuel Consumption During Exercise

2.4 Energy DensityEnergy Density (or calorie-density) is the number of calories per gram of a food item.

Higher energy density kcal/g

Taco shell 4.7Bologna 3.1Fried chicken 2.8Fried pork chop 2.8Cheseburger 2.7Hash brown potato 2.2Fried fish 2.2Fried rice 1.6Potato salad 1.4Sweetened Strawberries 1.1(frozen)

Low energy density kcal/g

Corn tortilla 2.2Sliced turkey breast 0.9Grilled chicken 1.7Broiled pork chop 2.0Bean burrito 1.9Broiled potato 0.9Broiled fish 1.2Rice 1.3Tossed salad (with dressing) 1.1Fresh Strawberries 0.3

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 CO2 produced to that of O2 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 BodyThe 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 MetabolismBasal 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 needs1. Determine BMR and calculate daily (24 hours) energy

requirement for basal metabolism2. 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 (~50 - 70%), physical activities (~15 - 30%), 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 ~15 - 30% 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 termsKilocalorie (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 CO2 produced to that of O2 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.

Fuel Homeostasis Quiz

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Charles Bell PhD bell.489@osu.edu

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