Lecture 4, Energy Expenditure

Question 1

Measuring the Body’s Heat Production

Answer 1

• all of the body’s metabolic processes ultimately result in heat production
• the rate of heat production operationally defines the rate of energy metabolism
• heat production = work = joules (J)
• calorie (unit)
  ◦ energy required to raise 1g of
  water 1 degree C
  ◦ kcal = “food calorie”
  ◦ 1 kcal = 4.184 kJ
• when you exercise you get hot where you transfer energy but is inefficient so we get heat production and that rate of heat production scales really well with the rate of energy expenditure
• we can also express heat as a calorie (how much are that food energy are you taking and doing work and how efficient are we)

Question 2

Direct Calorimetry

Answer 2

• apartments that people can live in to figure out how much heat the produce (how much influence exercise and different diets have on that)
• they pipe water in and out (well insulated) how much that water changes temperatures is related to how hard you are working and how much energy expenditure you have
• not something that we do on a regular basis as it is expensive
• direct calorimetry is where we measure heat production, as a form of energy expenditure

Question 3

Indirect Calorimetry

Answer 3

• all energy-releasing reactions in humans ultimately depend on oxygen use, so measuring oxygen consumption during physical activities provides an indirect yet accurate estimate of energy expenditure
• relatively simple and inexpensive
• two types:
  ◦ closed-circuit spirometry
  (complicated)
  ◦ open-circuit spirometry
  (measure the air that comes in
  and out)
• exploiting that chemical equations where we know we use oxygen and produce CO2 at fixed rates for a given amount of ATP production and substrate
• we measure expired gasses to find out energy expenditure
• we can measure oxygen and CO2 and figure out how much energy is being expended that way

Question 4

Components of Total Daily Energy Expenditure

Answer 4

• resting metabolic rate (same as basil metabolic rate) - energy your body requires for your body to not die for one day (sitting down not doing anything - energy required for breathing, to keep muscles from collapsing, and hormonal processes) - in many people this is the biggest source of energy expenditure
• physical activity energy expenditure - activities of daily living (the percentage will vary on how active you are - lower if sedentary)
• thermic effect of feeding - the energy it takes to digest food, when take complex molecules chew them up and break down into small molecules and store them as other molecules (proteins, fats, glycogens) - this takes up energy to break the food down and convert to other molecules
• this is important because we need to eat the right amount of food - if we eat too much food we accumulate body but if we eat too less then processes in the body cannot occur normally

Question 5

Estimating Resting Daily Energy Expenditure (RDEE)

Answer 5

0 usually expressed in kcal/h or kcal/d
◦ can be estimated from fat-free
mass (FFM)
◦ having more lean mass than
fat-free mass can have more
energy expenditure
◦ bigger people are going to
burn more energy than
smaller people
◦ the highest energy
expenditure in children and lowest in elderly people (after menopause of during menopause - around 50-60)

RDEE (kcal/d) = 370 + FFM (kg)

Question 6

Factors that Affect TDEE

Answer 6

1. physical activity (if you are more active you are going to burn more calories with a higher energy expenditure)
2. diet-induced thermogenesis (thermic affect of food - cost us ATP and oxygen to break down food - can modify this by eating more)
3. calorigenic effect on food on exercise metabolism (if you exercise right after you eat or eat right after you exercise you may be slightly less efficient and burn slightly more calories) - the effect is not huge
4. climate
5. pregnancy

Question 7

Climate

Answer 7

• environmental factors influence metabolic rate
  ◦ RMR of people in a tropical climate averages 5 to 20% higher than those living in temperate areas
• exercising in hot weather causes about a 5% higher O2 consumption
  ◦ results from an elevated core temperature, energy for sweat gland activity and altered circulatory dynamics
• cold environments increase energy metabolism during rest and exercise
  ◦ depends on body fat content and effectiveness of clothing
  ◦ you actually have to be cold to increase energy metabolism - if you are outside and wearing sufficient clothing you have not increased your energy expenditure
  ◦ can activate brown fat that is fat that is metabolic when you are cold
• climate can increase our energy expenditure and extreme climate (really cold or hot)
• thermoregulating and getting rid of heat is going to cost us energy and oxygen (higher consumption of oxygen and calories) - going to have higher blood flow to dissipate the heat - this is magnified even more if we were to be exercising

Question 8

Pregnancy

Answer 8

• added energy cost of weight-bearing locomotion during pregnancy results primarily from:
  ◦ additional weight transported
  ◦ reduced economy of effort from encumbrance of fetal tissue
• most of the change is due to changes in locomotion rather that the fetus
• increase in energy expenditure due to fetal tissue but is pretty small
• exercise during pregnancy is very important as there is no evidence that it is bad

Question 9

Physical Activity Affects on TDEE

Answer 9

• regular physical activity stimulates resting metabolism - EPOC
• each 1-lb gain in FFM increases RMR by 7 to 10 kcal/d
• exercise as a weight loss strategy?
  ◦ if TEE known and EX energy expenditure known can we predict weight loss? - yes
• if we exercise we burn calories during exercise and EPOC will burn calories as well - indirect calorimetry is the best way to measure how many calories you burn during exercise
• we can also increase resting metabolism by adding muscle but the effect is not huge
• if you are taking in more calories than you take out - weight gain (weight loss is the opposite) - this figure follows the law of thermodynamics
• if i were to measure both resting and physical activity EE you can figure out TEE and predict weight loss
• physical activity EE increase TEE a little bit but not nearly as much as would calculate

Question 10

Accommodation of energy expenditure

Answer 10

• resting energy expenditure is a fixed
• physical activity increase TEE a little bit but not nearly as much as would calculate
• we have this accommodation of decline in resting energy expenditure associated with increasing physical activity
• there are things in our resting metabolic rate are essential for us to thrive and there are things that are not essential that we doing to handle under exercise and over nutrition which can be detrimental(non-essential energy expenditure)
• as we become more and more active we decrease non-essential energy expenditure (so our TEE is not increasing as much as we think)
• if we start to overtrain and have under nutrition then it might start cutting into essential energy expenditure (uncommon)
• if we have low physical activity we have a high non-essential EE which means increased morbidity and mortality (opposite decreases the risk) - if we exercise normally both of these decrease - if we overexercise then there is also a slight increase into the 2 as we cut into essential EE
• overactive immune system is a bad thing - inflammatory response (if we exercise we reduce inflammation) white blood cell count can decline where there is a elevated risks of respiratory illness if we start overtraining as well
• hormonal function - stress hormones, cortisol, NE (using EE to have higher levels of those for that which is bad for our health) we can decrease stress hormones with exercise but too much and decrease the function too much then we lose essential function
• exercise is good to decrease the risk with the reproductive system cancers with is due to overproduction of cells
• if we do really extreme exercise with under nutrition there can be disruption in menstrual cycle

Question 11

Energy Balance Updated

Answer 11

increased exercise
* increased appetite and food intake - burn a certain amount of calories during exercise but your appetite increases at the same time
* decreased physical activity? - tired after physical activity so you have less movement which means total energy expenditure does not increase as much as you want
* more sedentary behaviour?
* exercise does not increase total energy expenditure but a predictable amount
dieting
* loss of lean mass (can decrease resting metabolic rate)
* decreased resting energy expenditure
◦ decreased sustained after end of diet
* caloric deficit must keep increasing to sustain weight loss
* this is easier in a short them sense but if you just eat less and do not do exercise 25% of the weight you lose is muscle (muscle is important for resting metabolic rate)
* physiologically weight loss can be hard (takeaway)