Appetite, hunger & the physiology of the fed and fasted state

Question 1

Identify and explain appetite

Answer 1

a psychological desire to eat

Question 2

Identify and explain hunger

Answer 2

the biological drive to eat

Question 3

identify and explain satiation

Answer 3

feeling of satisfaction that occurs during a meal, leading to termination of eating

Question 4

identify and explain satiety

Answer 4

feeling of fullness persisting after a meal

Question 5

homeostatic requirements vs hedonic mechanisms

Answer 5

hedonic - driven by the pleasure and comfort of food (sensory input)
homeostatic - driven by physical hunger

Question 6

Arcuate hypothalamus regulates appetite - it has two distinct neuron populations:

Answer 6

• NPY/AgRP orexigenic (appetite stim)
• POMC anorexigenic (appetite inhib)

Question 7

Leptin’s control mechanism

Answer 7

• appetite inhibition and basal metabolic rate increasing effect
• increases satiety and EE
• inhibits NPY/AgRP

Question 8

Leptin deficiency

Question 9

Ghrelin’s control mechanism

Answer 9

• reduces resting metabolic rate
• reduces lipolysis and increase the storage of fats in adipocytes
• Caloric restriction and weight loss have a strong impact on circulating ghrelin levels
  resulting in an increased appetite drive and impact on reducing metabolic rate

Question 10

GLP-1

Answer 10

• Anorexigenic
• via L cells
• reduces gastric emptying and improves insulin sensitivity and glucose uptake
• enhances satiety
• Butyrate and Propionate SCFA’s have role in stimulating release via L-cells

Question 11

PYY

Answer 11

• anorexigenic
• secreted by L-cells of small and large intestine
  -decreased levels observed in obesity
• like GLP-1, SCFAs have role
• increased levels following wt. loss surgery - role in appetite suppression

Question 12

CCK

Answer 12

• cholecystokinin
• anorexigenic - 1st discovered
• released by epithelial cells the Duodenum and Jejunum
• stimulates digestion via gall bladder contraction and pancreatic secretions
• inhibits stomach emptying, and reduces appetite via brain

Question 13

Fed state

Answer 13

• anabolic
• nutrients -> ATP for use or stored as glycogen or fat
• increased blood glucose stimulate insulin via beta islet cells
• high insulin/low glucagon
• glucose energy source
• excess glucose converted by liver to TAG - VLDL - adipocytes

Question 14

Fasted state

Answer 14

• catabolic
• mobilisation of stored glycogen and fat to provide energy
• decreased blood glucose stimulates glucagon and cortisol release via alpha islet cells
• low insulin/high glucagon
• glycogen exhausted
• incl. gluconeogenesis via aa’s
• FFA’s from lipolysis provide FFA’s for many tissues

Question 15

stages of fed-fast states

Answer 15

fed: 0-3 hours following meal
post-absorptive: 3-18 hours
fasted: 18-48 hours
starvation: >48 hours

Question 16

Post-absorptive

Answer 16

• increased glucagon excretion
• liver glycogenolysis and gluconeogenesis maintains BGLs
• lipolysis free FFA’s as energy source

Question 17

Starvation

Answer 17

• body prioritises protein sparing so aa’s rate of use is decreased
• accelerated lipolysis and use of FFA’s
• glycerol used for gluconeogenesis
• ketone bodies become major fuel

Question 18

Intermittent fasting and its health benefits

Answer 18

• metabolic benefits: continuous energy restriction (CER)
• involves fasting for varying periods of time, typ 12 hours or longer
• health benefits - wt. loss & metabolic switching

Question 19

Alternative Day Fasting

Answer 19

• no calories on one day followed by no restrictions following day

Question 20

Alternate Day Modified Fasting

Answer 20

• modified version of ADF
• allows low-calorie intake during fast day
• typ only 25% or less calories than a normal day

Question 21

5:2 and 4:3

Answer 21

• 2- or 3-day fasts followed by normal libitum eating for another 4-5 days
• ## gen <2000 kJ on 2 fasting days

Question 22

Eat-stop-Eat

Answer 22

a 24 hour fast once or twice a week

Question 23

Time Restricted Eating

Answer 23

• e.g. 16/8 eating pattern
• also called ‘circadian rhythm fasting’
• idea is to consume food when energy is mostly efficiently metabolised e.g. earlier in day when insulin sensitivity is highest

Question 24

Long-Term Adaptations of fasting

Answer 24

• increased:
  – insulin sensitivity
  – HRV
  – lipid metabolism
• healthy gut microbiota
• reduced:
  – abdominal fat
  – inflammation
  – blood pressure
• resilience
• disease resistance

Question 25

Fasting Safety Considerations

Answer 25

• trigger disordered eating
• not appropriate for some - pregnant, breastfeeding, children, ED, diabetes, some meds
• long-term not known
• safety in older adults not known
• risk of excess weight loss

Question 26

The three most studied intermittent fasting approaches

Answer 26

• alternate-day fasting
• 5:2
• daily time-restritced feeding