Nutritional Physiology lectures
Introduction to the course
Course learning objectives
• Describe and explain general digestive functions and main metabolic pathways
• Predict settings of metabolism based on nutritional input and physiological output
• Estimate changes in energetic efficiencies in relation to changing conditions
• Judge physiological conditions in terms of constrains for homeostatic control
Lecture 1: Digestive system
Mass flow of nutrients
Nutritional Input:
- Total daily intake (kJ)
- Meal size, pattern
- Nutrient composition
Physiological Output:
- Physiological status
- Health status
- Environment
Metabolism (constantly switching from nutritional input to physiological output to keep the balance):
- Metabolic pathways
- Energetic efficiencies
- Body composition - Waste products
Post-absorptive phase: metabolism from physiology (after fasting)
Post-prandial phase: metabolism from nutritional input (after eating)
Nutritional physiology
Dietary components – Nutrients:
- Macronutrients (carbohydrates, proteins, fat)
- How do they move through the body?
Translocation: to different positions
Transformation: adapted and broken down in different
structures (e.g. monomers)
- How are these movements regulated?
Neural system
Endocrine system (hormonal)
- What are physiological options/benefits for the body?
- How do nutrients leave the body? → after oxidation → CO2, leave via the lungs by
exhalation
What happens after eating?
Hardly any influence on the fate of the food after swallowing!
- Digestion and absorption
- Storage
- Utilisation
Increasing interest in feeding strategies aimed to influence the fate of the food
Balance: Nutritional Input ⇌ Metabolism ⇌ Physiological Output
,Digestion → Fermentation
Microbial fermentation may provide energy, but NO amino acids!
GI tract works as a factory
After uptake in circulation, it can be used as energy or it can be stored
Enzymes are needed for digestion: they lower the activation energy of
proteolysis (breakdown)
Specificity: one enzyme for specific amino acids
Highly dedicated and well-defined
Why does the digestive system not digest itself?
1. Activity restricted to presence of food (no release of enzymes when sleeping, because there
is no food present)
2. Regulation (local, distal, proximal)
3. Enzymes stored as inactive pro-enzymes (zymogens)
4. Non-digestible mucus coats the walls: layer in intestines that protects the wall from being
digested by enzymes that are released into the lumen of the intestines
5. High replacement rate (turnover) of mucosal cells: new cells produced to replace the older
ones, highest replacement rate in the intestine
All have an influence on metabolic settings
Settings of metabolism
- First: Digestion to and absorption of monomers
- Then: Intermediary metabolism
Interconversions of absorbed monomers
Anabolic reactions (e.g. protein metabolism): synthesis of body constituents
Catabolic reactions (Energy / ATP / Heat): release of energy from food or body
constituents
Unavoidable waste products
- Time scale of events (post-prandial vs. post-absorptive)
- Physiological adaptation
Intermediary cellular catabolism
,Meal feeding ~ Metabolic changes
Post prandial phase (after eating) → Digestion – Absorption – Storage:
INPUT > NEEDS → ANABOLIC or CATABOLIC DISPOSAL
→ storage, interconversion, oxidation (to continuously fuel the body with
energy)
Post absorptive phase → Utilisation:
INPUT < NEEDS → MOBILISATION (degrading)
→ turnover, interconversion, oxidation (breakdown of your stores)
Thermogenic effects of a meal aka Diet-induced Thermogenesis (DIT)
- Post prandial metabolism (PPM) increases heat production (5 - 20% ingested ME =
metabolizable energy)
- This mechanism always happens, so when cold: start to eat!
- Effects depend on ingested nutrients: proteins > carbohydrates > fat
- Ingested ME is not corrected for energetic costs of PPM: the food labeling in kJ/kcal is truly
your metabolizable energy without correction for your losses in heat
Storage of nutrients: mainly in fat tissue, but also in the muscle
Homeostasis: ability of an organism to counteract (within limits of the metabolic scope)
factors that disturb vital functions
- Glucose concentration in blood
- pH in the blood (acid - base balance)
- Oxygen supply (cardiac output, respiration)
- Body temperature (thermoregulation)
Homeostasis: conflict of interest between body → metabolism
Metabolism provides body with energy, but at the same time: heat production
The body wants a certain temperature threshold, so metabolism needs to go down
Constant balance between energy level and temperature level!
Energy balance
Input: energy intake
Output: energy expenditure
Balance at different levels of intake and expenditure
Relation intake ~ expenditure of energy (figure)
A positive energy balance: overweight & obesity
, Multiple choice exam question: The settings of metabolism can be influenced
by:
a) Environmental conditions
b) The nutritional input
c) The physiological output
d) All answers above are correct
Digestive system: the integrated response to a meal
1. General features and goals
Transfer
- Food and body are both characterised by specific macromolecular constituents, synthesized
from the same (non-specific) monomeric components
- Transfer of monomers from food to body requires digestion to absorbable (water soluble)
components and absorption
- Protection against auto-digestion (mucus, high cell-turnover)
Digestive tract (GI tract)
- Outside world inside
- Hollow tube (7 m) from mouth to anus
- Functional compartments: each compartment has its own role
- One-way transport
- Indigestible material doesn’t enter the body, it remains in GI tract and is excreted
GI tract is largely similar between different species
After ingestion: motor behavior & secretion in order to digest and absorb the monomers
Multiple organs: oral cavity, salivary glands, stomach, small intestine, colon, pancreas (production of
enzymes), gallbladder (stores the bile) → accessory organs
2. Anatomy
Mouth → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine →
rectum → anus
Also absorption of water in the small intestine: because there is also water produced there
Introduction to the course
Course learning objectives
• Describe and explain general digestive functions and main metabolic pathways
• Predict settings of metabolism based on nutritional input and physiological output
• Estimate changes in energetic efficiencies in relation to changing conditions
• Judge physiological conditions in terms of constrains for homeostatic control
Lecture 1: Digestive system
Mass flow of nutrients
Nutritional Input:
- Total daily intake (kJ)
- Meal size, pattern
- Nutrient composition
Physiological Output:
- Physiological status
- Health status
- Environment
Metabolism (constantly switching from nutritional input to physiological output to keep the balance):
- Metabolic pathways
- Energetic efficiencies
- Body composition - Waste products
Post-absorptive phase: metabolism from physiology (after fasting)
Post-prandial phase: metabolism from nutritional input (after eating)
Nutritional physiology
Dietary components – Nutrients:
- Macronutrients (carbohydrates, proteins, fat)
- How do they move through the body?
Translocation: to different positions
Transformation: adapted and broken down in different
structures (e.g. monomers)
- How are these movements regulated?
Neural system
Endocrine system (hormonal)
- What are physiological options/benefits for the body?
- How do nutrients leave the body? → after oxidation → CO2, leave via the lungs by
exhalation
What happens after eating?
Hardly any influence on the fate of the food after swallowing!
- Digestion and absorption
- Storage
- Utilisation
Increasing interest in feeding strategies aimed to influence the fate of the food
Balance: Nutritional Input ⇌ Metabolism ⇌ Physiological Output
,Digestion → Fermentation
Microbial fermentation may provide energy, but NO amino acids!
GI tract works as a factory
After uptake in circulation, it can be used as energy or it can be stored
Enzymes are needed for digestion: they lower the activation energy of
proteolysis (breakdown)
Specificity: one enzyme for specific amino acids
Highly dedicated and well-defined
Why does the digestive system not digest itself?
1. Activity restricted to presence of food (no release of enzymes when sleeping, because there
is no food present)
2. Regulation (local, distal, proximal)
3. Enzymes stored as inactive pro-enzymes (zymogens)
4. Non-digestible mucus coats the walls: layer in intestines that protects the wall from being
digested by enzymes that are released into the lumen of the intestines
5. High replacement rate (turnover) of mucosal cells: new cells produced to replace the older
ones, highest replacement rate in the intestine
All have an influence on metabolic settings
Settings of metabolism
- First: Digestion to and absorption of monomers
- Then: Intermediary metabolism
Interconversions of absorbed monomers
Anabolic reactions (e.g. protein metabolism): synthesis of body constituents
Catabolic reactions (Energy / ATP / Heat): release of energy from food or body
constituents
Unavoidable waste products
- Time scale of events (post-prandial vs. post-absorptive)
- Physiological adaptation
Intermediary cellular catabolism
,Meal feeding ~ Metabolic changes
Post prandial phase (after eating) → Digestion – Absorption – Storage:
INPUT > NEEDS → ANABOLIC or CATABOLIC DISPOSAL
→ storage, interconversion, oxidation (to continuously fuel the body with
energy)
Post absorptive phase → Utilisation:
INPUT < NEEDS → MOBILISATION (degrading)
→ turnover, interconversion, oxidation (breakdown of your stores)
Thermogenic effects of a meal aka Diet-induced Thermogenesis (DIT)
- Post prandial metabolism (PPM) increases heat production (5 - 20% ingested ME =
metabolizable energy)
- This mechanism always happens, so when cold: start to eat!
- Effects depend on ingested nutrients: proteins > carbohydrates > fat
- Ingested ME is not corrected for energetic costs of PPM: the food labeling in kJ/kcal is truly
your metabolizable energy without correction for your losses in heat
Storage of nutrients: mainly in fat tissue, but also in the muscle
Homeostasis: ability of an organism to counteract (within limits of the metabolic scope)
factors that disturb vital functions
- Glucose concentration in blood
- pH in the blood (acid - base balance)
- Oxygen supply (cardiac output, respiration)
- Body temperature (thermoregulation)
Homeostasis: conflict of interest between body → metabolism
Metabolism provides body with energy, but at the same time: heat production
The body wants a certain temperature threshold, so metabolism needs to go down
Constant balance between energy level and temperature level!
Energy balance
Input: energy intake
Output: energy expenditure
Balance at different levels of intake and expenditure
Relation intake ~ expenditure of energy (figure)
A positive energy balance: overweight & obesity
, Multiple choice exam question: The settings of metabolism can be influenced
by:
a) Environmental conditions
b) The nutritional input
c) The physiological output
d) All answers above are correct
Digestive system: the integrated response to a meal
1. General features and goals
Transfer
- Food and body are both characterised by specific macromolecular constituents, synthesized
from the same (non-specific) monomeric components
- Transfer of monomers from food to body requires digestion to absorbable (water soluble)
components and absorption
- Protection against auto-digestion (mucus, high cell-turnover)
Digestive tract (GI tract)
- Outside world inside
- Hollow tube (7 m) from mouth to anus
- Functional compartments: each compartment has its own role
- One-way transport
- Indigestible material doesn’t enter the body, it remains in GI tract and is excreted
GI tract is largely similar between different species
After ingestion: motor behavior & secretion in order to digest and absorb the monomers
Multiple organs: oral cavity, salivary glands, stomach, small intestine, colon, pancreas (production of
enzymes), gallbladder (stores the bile) → accessory organs
2. Anatomy
Mouth → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine →
rectum → anus
Also absorption of water in the small intestine: because there is also water produced there
