FOOD20003 Lecture Notes - Lecture 23: Ghrelin, Leptin, Orexin
28 Jun 2018
School
Department
Course
Professor
ENERGY BALANCE
Main considerations
• Excessive and deficient body fat results from energy imbalance
• Body weight is stable when energy consumed = energy expended
• Energy not used à stored as fat in fat cells
• Accumulation of excess fat à health risks (i.e. heart disease, obesity etc)
o Excess fat in abdominal area = most serious risk
• All three macronutrients can be converted to storage fat
o Proteins à structural
o Carbs à first energy source
o Fats are usually turned into body fat first
o Also easier to convert dietary fat à body fat
o So reducing fat intake = best effect in reducing body fat
o BUT must ensure that particular MUFA/PUFA are still present in diet
Food composition
• Use bomb calorimeter
• Similar to human cell but more efficient in capturing energy in kJ (not ATP) released
• Been mathematically adjusted to fit the efficiency of mitochondria in our body
• Food is burned to CO2 + H2O, and heat released is measured
Energy balance
• Through digestion/absorption à food broken down that can enter cellular energy
metabolic pathways
• Energy not required à re-incorporated as fat
• Energy is used by the body in the form of:
o Basal metabolism (60-70%)
o Exercise (15-25%)
o Thermic effect of food (10%)
o Adaptive thermogenesis ß due to altered conditions, may be 0%
Control of food intake
• Appetite = desire to eat à initiates through sight, smell, thought or taste
o Close interplay between digestive tract, adipose & brain (nerve & hormone signals)
o Anorexia = decreased desire to eat
o Hyperphagia = increased eating
• Hunger = motivates us to eat
o Controlled by hypothalamus
• Satiation = stop eating
o Receptors in the stomach stretch and hormones such as cholecystokinin increase
• Satiety = remind us not to eat again until body needs food
