KPE371: Lecture 2

Causes of obesity

diet

genes/environment (built and food environment)

physical activity

individual behaviours

socioeconomic status/cultural influences

economic growth

macrolevel forces

global free trade

urbanization

AND

Obesity occurs when energy in is greater than energy out consistently over time

what determines energy balance

• The relationship between energy intake and energy expenditure (in and out)

• energy in: food and drinks that contain energy

• energy out: basal metabolic rate (BMR) or resting metabolic rate (RMR), thermic effect of food, physical activity

  • The amount of energy needed at rest for the body to stay alive

  • BMR is done while fasted

energy intake has increased over the years

• 24% in calorie intake since 1961

• 800kcal increase

• 62% of the Canadian diet is processed and ready-to-eat food

Study on freshman15

• 300 students at brock university

• males gained 8 pounds, females gained 4 pounds

• men displayed lower quality eating patterns

• men had a greater increase in waist ratio and abdomen fat

Energy out: Resting metabolic rate

• the amount of energy needed to maintain metabolic processes at rest

• measured in the fasted state

• 1kcal/kg body weight/hr

• can determine how many kcal someone would burn over 24hrs

How do we actually measure RMR

• calorimetry

  • Quantification of energy production by the body

• direct calorimetry

  • measuring heat production

• indirect calorimetry

  • measuring oxygen consumed and carbon dioxide produced

  • L/min or ml/kg/min

  • 1 L of O2 consumed = 5 kcal expended

significant contributors to RMR

• fat free mass and fat mass

• higher muscle mass = more energy needed bc muscle is a very active metabolic tissue

  • people who are obese also have a higher RMR and just because they are obese doesn’t mean they have to eat little calories

Your friend signed up for a research study and looks to you to understand more about the measurements. She tells you they will measure how many calories she burns while lying down with some kind of mask. Please answer the following:

1. Explain to your friend what this test is and what the researchers are measuring.

2. The researchers tell your friend her RMR is 1433kcal. How would you explain to Katie what this number means?

3. How did the researchers use the results of this test to calculate that your friend’s RMR was 1433kcal?

4. If Katie then consumes 2300kcal in a day, what will dictate whether she is in a positive or negative energy balance?

1. They are measuring her resting metabolic rate which is the energy used at rest which is able to determine the type of fuel they are able to use. We can determine how much energy and what type of molecule they are burning

2. This means Katie’s body burns about 1433 kcal per day at rest, without any movement or exercise. It’s the minimum energy her body needs to function and stay alive.

3. They used a method called indirect calorimetry, measuring oxygen consumption (VO₂) and carbon dioxide production (VCO₂). Since energy production requires oxygen and releases CO₂, they can calculate energy expenditure in kcal from these gas exchange values.

4. We need to know the energy out (thermic energy, PA, etc). Her personal and lifestyle life. Like if she is an athlete which will help determine if that number is a good number for her

the math of Katie BMR = 1433 kcal per day, how did we get to this number..

• 1433/ 5 (bc this is for every L O2 consumed)

• 286.6/ 24 h/day

• 11.94/ 60 min/hr

• 0.20 L O2/min

if we knew Katies weight ( 55kg)

• 0.20/55

• 0.0036 × 1000

• 3.6 ml/kg/min

Declines in physical activity over time

• only 15% of adults are getting the recommended 150 min of physical activity per week

• moderate exercise jobs have decreased over the years and light exercises jobs have increased showing the contribution to obesity

MET

• metabolic equivalence of task

• used to determine the metabolic activity of a person

  • 1 MET = resting energy burned

  • 2 MET = 2 times your resting energy expedenture

  • and so on

why cant we loose anymore weight even though we are eating fewer calories

• If my caloric maintenance (amount of food normally consumed to maintain current bodyweight) is 2500 calories, and i cut off 500 so that i lose weight, i will get to a point where i wont loose anymore weight. so 2000 calories will be my new maintenance. in order to continue losing more weight i have to cut off another 500 calories.

how much can one pound of fat store

• 3500 kcal

calories in and out are not independent

• they influence each other

• eating less reduces calories out (bc staving urself makes u store the food)

• eating more increases metabolism in some cases

evolutionary context

• being underweight was common (had to hunt for food)

• our bodies havent adapted to our mostly sednenetary lifestyle

• when we starve ourselves and then eat food, our body stores the food that we eat aftweards bc it dooesnt know when tis going to get food again

when losing weight.. (feedback regulation)

Calories out (decreases)

• RMR drops

• 25 kcal/day less is burned per kg lost

• body requires less energy bc its smaller and more efficient

calories in (increases in hunger)

• brain increases appetite to restore lost weight

• 95 kcal/day more hunger per kg lost

• makes you want to eat more food

endocrine system limits continued weight loss

• endocrine system has lots of hormones that increase our hunger

• leptin is a hormone that stimulates the brain to stop eating

• the more weight that people lost, the more drop in leptin meaning that people felt less full (low leptin = more hunger)