Calories and diet - Lecture notes 7 PDF

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Calories and diet in biochemistry....

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Calories and Diet

1 Copyright Dr Steven Bottomley

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Calories, Diet, and Nutrition • • • • • • •

The measurement of energy ‘Calorie’, calorie, and joule Energy value of foods Energy expenditure in humans Caloric homeostasis Diet Metabolic efficiency Nutrition concerns

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Energy and the ‘Calorie’ • •

•

calorie (small ‘c’ calorie) = energy required to raise temperature of 1g water by 1 degree Celsius at 1 atmosphere pressure Calorie (large ‘C’ calorie or the Calorie used in nutrition and diet) = energy required to raise temperature of 1kg water by 1 degree Celsius at 1 atmosphere pressure 1Calorie = 1000 calories Joule • 1cal = 4.18J • 1kcal = 1Cal = 4.18kJ

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Calorimetry

From: /wps.prenhall.com/wps/media/objects/602/616516/Chapter_08.html 4 Copyright Dr Steven Bottomley

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Energy value of foods Fuel

Energy Yield kJmol-1

kJg-1

2815

15.6

10,040

39.2

979

13.1

carbohydrate

Not applicable

16

6.3

fat

Not applicable

37

37

protein

Not applicable

17

6.3

ethanol

1334

29

Not applicable

48

glucose Palmitic acid glycine

Oil (for comparison)

kJg-1 wet weight

Adap ted From: W rigglesworth (1997) 5 Copyright Dr Steven Bottomley

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Energy value of foods • • •

Energy released from burning food in calorimeter = energy released from metabolism Energy released from calorimeter = heat Energy released from food in metabolism = work + heat • eventually most of this metabolic work is also converted to heat

•

About 10 000 J/day (10MJ) is the usual daily energy requirement for humans

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Energy value of foods What is energy used for? •

Resting (basal) Metabolic rate (RMR or BMR) • Rate of heat produced (energy used) by person at rest, no physical work, in postabsorptive state • Energy for respiration, blood flow (heart contractions) and all cellular metabolism (including ion transport, synthesis, etc) • BMR about 10% higher than sleeping metabolic rate • About 60% of total energy expenditure (6000 kJ/day)

•

Thermic effect of food • Body produces heat above resting level when food is digested and absorbed • About 10% of total energy expenditure

•

Physical activity • Highly variable and depends upon duration and intensity of exercise • About 30% of total energy expenditure Refer to C hamp e et al. (2005) p357 7

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Energy Expenditure in Humans

Time (min)

Energy Cost (kJmin-1)

Total daily Energy expenditure (kJ)

lying

540

5.0

2700

sitting

600

5.9

3540

standing

150

8.0

1200

walking

150

13.4

2010

TOTAL

1440

-

9450

Activity

From: W rigglesworth (1997)

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Energy Expenditure

Eventually all work is converted to heat

Food Intake (10MJ/day)

Metabolism Weight Gain

10MJ/day equivalent to 1.6 kg carbohydrate or 0.27 kg fat or 1.6 kg protein

Work

Heat

Weight Loss

Body Stores Fat Protein Carbohydrate

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Energy from Glucose C6H12O6 + 6O2 = 6CO2 + 6H2O + energy 2815kJ/mol In Calorimeter Heat

In cell (metabolism) Glycolysis TCA cycle Electron transport & Oxidative phosphorylation

Heat

ATP Work 10

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Efficiency of Energy from Glucose

C6H12O6 + 6O2 + 33ADP + 33Pi = 6CO2 + 6H2O + 33ATP*

Energy in ATP 31kJ/mol in standard state

50kJ/mol in cellular conditions

31kJ/mol x 33ATP 2815kJ/mol

50kJ/mol x 33ATP 2815kJ/mol

1023 kJ/mol 2815kJ/mol 36%

1650 kJ/mol 2815kJ/mol Efficiency

59%

* Estimate of ATP produced varies dep ending up on values used for NADH and FADH conversion to ATP Copyright Dr Steven Bottomley

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Diet & Energy Expenditure Calorie Restriction

Food Intake (Carbohydrate, fat, & protein)

Metabolism

Work

Heat

Weight Loss

Body Stores Calorie Restriction & Increased work

Fat Protein Carbohydrate Increased work (exercise)

Food Intake (Carbohydrate, fat, & protein)

Weight Loss

Metabolism

Work

Heat

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Diets (isocalorie diets) ‘Typical’ Western Diet Fat 38%

Carbohydrate 42%

Protein 20%

Low Fat Diet 4%

65%

15%

Low Carbohydrate Diet/ High Fat 65%

15%

20%

Low Carbohydrate Diet/ High Protein 40%

50%

10%

Acceptable Macronutrient Distribution Ranges (AMDR)* 20-35%

45-65%

10-35%

* ”Range of intake for a particular macronutrient that is associated with reduced risk of chronic disease while providing adequate amounts of essential nutrients” C hamp e et al. (2005) p358 Copyright Dr Steven Bottomley

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Diet & Energy •

All diets of equal caloric content are assumed to be ‘processed’ identically regardless of their macronutrient composition. • That is the energy content of a diet will be realised despite various amounts of fats, carbohydrates, or proteins in the diet • A calorie is a calorie no matter where it comes from

•

There should be no difference between low carbohydrate, low fat, or high protein isocaloric diets

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Metabolic Advantage • • •

Concept that that there weight loss depends upon macronutrient composition in different isocaloric diets In particular, it has been said that low carbohydrate diets induce more weight loss that isocaloric diets containing high carbohydrate Does metabolic advantage contravene the laws of thermodynamics? • A calorie is a calorie no matter where it comes from

•

1st law of thermodynamics is satisfied • provided that all energy in is equal to all energy out (in terms of entropy, heat, and mass of molecules excreted)

•

2nd law of thermodynamics • There is an inefficiency inherent in biological systems • That is some of the energy of food is lost as heat to increase entropy • As long as entropy increases the 2nd law is not contravened

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Metabolic Efficiency Calorimeter

3.6 C6H12O6 + 22O2 = 22CO2 + 22H2O + heat Cell (where energy is required for BMR)

3.6 C6H12O6 + 22O2 = 22CO2 + 22H2O + heat TAG

120ADP

120ATP

Calorie Restriction - Eat less & lose weight

3 C6H12O6 + 18O2 = 18CO2 + 18H2O + heat Lose Weight

100ADP

TAG

100ATP 120ATP

20ADP Fatty Acids

20ATP CO2 + H2O + heat Adapted from: Fine & Feinman (2004)

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Metabolic Efficiency Reduced Efficiency (from 59% to 53%): Eat more & maintain weight

4 C6H12O6 + 24O2 = 24CO2 + 24H2O + heat TAG

120ADP

120ATP

Reduced Efficiency (from 59% to 53%): - Eat same amount & lose weight

3.6 C6H12O6 + 22O2 = 22CO2 + 22H2O + heat Lose Weight

112ADP

TAG

112ATP 120ATP

8ADP Fatty Acids

8ATP

CO2 + H2O + heat Adapted from: Fine & Feinman (2004)

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Metabolic Advantage - mechanisms? •

How could metabolic advantage occur? •

•

Looking for mechanisms that decrease metabolic efficiency of energy conversion to ATP

Oxidative uncoupling •

Endogenous agents in diet? • DNP is a pharmacological agent but illustrates the point of an ‘agent’ that can cause oxidative uncoupling

•

Genetics? • Alterations in uncoupling proteins (UCP)

•

Substrate (futile) cycles •

•

Metabolic path of macronutrient •

• •

Substrate cycles are known to be inefficient in terms of ‘wasting’ ATP and generating heat The metabolic path the macronutrient takes may involve inefficiency

Protein induced protein turnover (thermogenesis) Gluconeogenesis induced protein turnover

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Oxidative Uncoupling Normal coupling H+ Mitochondrial Intramembrane Space

H+

H+

H+

H+

H+

H+

ATP Synthetase

Electron Transp ort C hain

Mitochondrial Matrix

ADP + Pi

Uncoupling H+ Mitochondrial Intramembrane Space

H+

H+

H+

H+ H+

H+ ATP Synthetase

Electron Transp ort C hain

Mitochondrial Matrix

ATP

ADP + Pi

Uncoupling promotes the mobilisation of energy stores (such as fat) to provide energy (through Gluconeogenesis and glycolysis. Copyright Dr Steven Bottomley

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Substrate Cycles Enzyme X (100 pmol/cell/s) ATP

ADP

A

B

Pi

H2O Enzyme Y (80 pmol/cell/s)

If Enzyme X increased 10% then flux increases 30 pmol/cell/s in direction of B An increase of 50% in flux from A to B and increase in consumption of ATP 20 Copyright Dr Steven Bottomley

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Metabolic Path Ketones

CO2+H2O

CO2+H2O

Triglyceride turnover: 2% energy loss compared with direct oxidation of fatty acids ATP

Fatty Acids

ADP

Triacylglycerol (TAG)

CO2+H2O ATP

ADP

CO2+H2O Ala CO2+H2O

CO2+H2O Glucose

Amino Acids

Glycogen CO2+H2O

CO2+H2O

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Glycogen turnover: 5% energy loss compared with direct oxidation of glucose

Proteins

ADP

ATP

Protein turnover: 18 to 27% energy loss compared with direct oxidation of amino acids Feinman & Fine (2003)

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Gluconeogenesis

Low carbohydrate

gluconeogenesis

Protein Turnover

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Protein induced protein turnover

Low Carbohydrate/high protein diet

Protein Turnover

Heat (thermic effect of food)

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Diet and Metabolism

I can eat lots and don’t gain weight. I must have good metabolism

Is it ‘good’ or is it inefficient?

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Diet and Nutrition •

•

Low carbohydrate, high fat, low fat, high protein, low protein. Whatever the diet it is essential that the nutritional requirements are met! Dietary fats should include ‘essential fats’ – Omega 6 fatty acids eg. Linoleic acid – Omega 3 faty acids eg. Linolenic acid, docosahexenoic acid (DHA), eicosapentaenoic acid (EPA)

•

Carbohydrates – Soluble and insoluble fibre – Protein sparing effect of carbohydrates

•

Proteins – Source of essential amino acids and branched chain amino acids – Protein - calorie nutrition • Kwashiorkor – Total caloric intake ‘normal’ but total protein reduced

• Marasmus – Total caloric intake reduced greater than protein reduction (but protein intake still reduced) 25 Copyright Dr Steven Bottomley

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References • • • • • •

Champe et al. (2005) Biochemistry 3rd Edition. Lippincott Williams & Wilkins. Feinman, R.D. and Fine, E.J. (2003) Thermodynamics and Metabolic Advantage of Weight Loss Diets. Metabolic Syndrome & Related Disorders 1: 209-219 Fine, E.J. and Feinman, R.D. (2004) Thermodynamics of weight loss diets. Nutrition & Metabolism 1:15 Gibson, D.M. & Harris, R.A. (2002) Metabolic Regulation in Mammals. Taylor and Francis London & New York Nelson, D.L. & Cox M.M. (2005) Lehninger. Principles of Biochemistry. (4th ed). WH. Freeman & Company New York. Wrigglesworth, J. (1997) Energy and Life. Taylor & Francis. London

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