fed + fasting pathways

energy balance equation

total caloric intake - total energy expenditure

balanced energy

intake = TEE

stable weight

positive energy balance

intake is greater than TEE

weight gain

negative energy balance

intake is less than TEE

weight loss

cals for 1 lb of body fat

3500-3600 kcal

cal deficit for 1lb loss per week

500 kcal/day deficit

cals for +10 lbs in a year

+100 kcal/day

total energy expenditure equation

thermic effect of a meal + physical activity + basal metabolic rate

main determinant of energy expenditure

basal metabolic rate

thermic affect of food

energy expended to digest and absorb food

varies with composition of meal

very small % of total energy

what varies physical activity for energy expenditure

age and intensity

physical activity guidelines (based on % above BMR)

sedentary 20-40% above BMR

light 50-65% above BMR

moderate 70-75% above BMR

heavy 80-100% above BMR

basal metabolic rate

energy expended to carry out essential body functions: heart, brain, kidneys, etc, biochemical reactions, thermogenesis

what varies BMR

1. lean body mass

2. hormones (thyroid, sex hormones, inulin + glucagon)

3. stress (acute stress= weight loss, chronic stress= weight gain)

4. genetics!!!!!!!

main determinant of BMR

lean body mass

muscle is more metabolically active than fat

(men have more LBM than women)

why do men have higher BMRs than women

they have more lean body mass

what tissue type if more metabolically active

muscle (way more than fat)

ways to measure BMR via gas exchange

awake

laying down

12 hr post prandial (not digesting big meal)

comfortable room temperature

Harris Benedict equation

Men: BMR= 66.5 + 13.7 (W) + 5 (H) - 6.8 (A)

Women: BMR= 655.1 + 9.56 (w) + 1.85 ( H) - 4.7 (A)

W= body weight in kg (1kg = 2.2 lbs)

H = height in cm (1in = 2.54 cm)

A= age in years

what was Harris Benedict equation made for

military = fit population

multiply result of Harris Benedict equation by what to get Total Daily Energy Expenditure

activity factor

activity factor for relatively fit person

x 1.2

activity factor for very fit person

x 1.5

Mifflin St. Jeor equation

Men: (10 x W) + (6.25 x H) - ( 5 x A ) + 5

Women: (10 x W) + (6.25 x H) - ( 5 x A ) + 161

USDA for cals per day

2000-2500 kcal/ day (rounded number)

(depends on gender and level of physical activity)

safe rate of weight loss per week

no more than 1-2 lbs (burning fat mass and not muscle)

no dehydration

sustained rate of weight loss

more than 1-2 lbs per week of weight loss is really loosing what

water weight and tissue

refeeding syndrome

someone severely underweight is fed too rapidly (CHO specifically)

what does fed state promote

storage

fed state hormone

insulin

what does fasting state promote

energy production

fasting state hormone

glucagon

fed state metabolic pathways

glycogenesis

HMP Shunt

TG synthesis

FA synthesis

cholesterol synthesis

fasting state metabolic pathways

glycogenolysis

gluconeogenesis

lipolysis

ketogenesis

pathways what happen regardless of fed or fast state

glycolysis

beta oxidation

krebs

how fast does liver glycogen deplete during fasting

around 12 hrs

what happens to glucagon during fasting

increases

what happens to insulin during fasting

decreases

what happens to ketone levels during fasting

increases

what happens to FFA levels during fasting

increases

what happens to blood glucose during fasting

small drop after a few hours then levels out

what happens to liver glycogen during fasting

steady decline until depletion

energy state during fed state

excess

energy state during fast state

deficit (starvation/survival mode)

primary hormone in fed state

insulin

carb general pathway in fed state

glucose → liver and muscle glycogen → change CHO/fat expenditure → fat storage

fat general pathway during fed state

fatty acids → fat storage

protein general pathway during fed state

AAs → refill AA pool → protein formation → fat storage

glucose dependent tissues

RBCs, brain, CNS

what is affected by switching to ketones

brain “fasted feeling”

initial response to fasting

1. glucose levels drop

2. glycogen stores are broken down to maintain glucose

3. circulating AAs used for gluconeogenesis

4. FAs begin to be released in higher quantity

response to first few days of fasting

1. use glucogenic AAs to keep up levels of glucose to supply brain, CNS, and RBCs

2. FAs in other parts of body metabolized to ketones

response to first few weeks of fasting

1. body looks to conserve energy

2. lowers body temp, BP, and kidney function

3. minimal gluconeogenesis to spare body protein

4. ketone production increases

5. brain begins to adapt and use ketones for energy

response to several weeks of fasting

1. immune system severely diminished

2. fat stores nearly depleted

3. body beings to use lean body mass for energy (PEM= protein energy malnutrition)

fasting response near death

organs begin to be broken down for energy

nitrogen balance for someone who is fasting

very negative

no nitrogen coning in from eating proteins + lots of nitrogen excreted through urea cycles from breaking down AAs for energy for Krebs cycle