Energy in Food and BMR Flashcards
Macronutrition is the study of
obtaining energy to fuel normal activity
Faulty nutrition (under and over) is a major cause of
disease, along with infection and inherited abnormalities
A typical adult needs how many MJ of dietary energy per day?
10MJ
How does dietary energy leave the body?
10MJ of energy taken up per day is radiated as heat (100W) regardless of the work performed
What is the BMR?
a measurable quantity that is the minimum energy to sustain life; energy to pump blood, sustain cellular processes, and minimal metabolic activity to maintain 37 degrees body temperature
Exercise is usually what % of typical daily energy expenditure?
20-40%; critical for health and weight control
What is a bomb calorimeter?
it gives a direct measure of the energy of combustion in food to H2O, CO2, NO, and heat; food is combusted under pressurized oxygen in a chamber and the amount of heat released is measured
What is an Atwater chamber?
70kg male medical student in a chamber; over 4 days measured daily averages in MJ of energy content of food, energy supplied from body reserves (fat and protein), faecal and urinary waste energy; calculated the energy obtained from food and depletion of reserves and the heat output - 10MJ per day
1 Watt =
1 joule/sec (100W radiated per day)
What is the first law of thermodynamics?
energy can neither be created nor destroyed, only transformed - the energy of sunlight becomes the stored chemical energy of glucose which we eat
Fat produces how many kJ/g?
37
Alcohol produces how many kJ/g?
30
Carbohydrates produce how many kJ/g?
17
Protein produces how many kJ/g?
16
Alcohol is metabolised to
acetate by alcohol dehydrogenase and aldehyde dehydrogenase; becomes Acetyl-coA
BMR takes up how much energy per day?
60-70% (6-7MJ)
Specific dynamic effect
aka postprandial thermogenesis, heat increment of feeding, diet induced thermogenesis; 8-10% of energy turnover (elevated by high protein diet) ie expended in absorption and transport of nutrients, digestive enzyme synthesis, gut mobility, and gut replacement
BMR is measured
in subjects at rest 12 hours after eating in a thermoneutral environment of 25-30 degrees C
Thermal efficiency is determined by
a lower area/volume; larger bodies are more efficient (have lower BMR)
How does age affect BMR?
newborns use about 15% of energy for growth; children have higher MR due to size and growth; adult BMR decreases by 2% every 10yrs after age 20
What affect does high body fat have on BMR?
high body fat decreases BMR; fat cells need little energy to store TAGs tf high fat = low energy consumption and greater insulation to heat loss
Why do females have lower BMR?
higher adiposity (20-30%) for reproductive health
Why do males require more energy per day?
Leaner body mass, requires ~1MJ more energy
