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NP01- Mass flow of nutrients (through the body and its cells)
3 balancing aspects in nutritional physiology – in balance
Post-absorptive phase: in the morning when you get up: you rely on the energy in your body
The metabolism is constantly switching in pathways and energetic efficiencies à might affect body composition
Nutritional input Physiological input: Metabolism
- Total daily intake (kJ) - physiological status - different metabolic pathways
- meal size, pattern - health status - different energetic efficiencies (do
- nutrient composition - environment you need more heat or more energy)
= whatever you eat - If start to exercise à need more energy - different body composition – waste
- If you’re really old à need also energy products
Dietary components – nutrients:
Macronutrients bring the energy: carbohydrates, proteins, fat
They moved through the body via:
§ Translocation (from different positions) AND
§ Transformation (adapted and broken down in different structures: ultimately into monomers so they
can be absorbed in the GI tract)
à regulated by the neural system and the endocrine system (hormones)
How do nutrients leave the body? à via the lungs as CO2. The majority of the nutrients are being oxidized (to
provide energy to the body) and they are producing CO2 when oxidized à so they are exhaled
à big difference between what you eat (nutrients) and what you exhale (CO2)
What happens after eating?
We hardly have any influence on the fate of food after swallowing it. You can’t determine with your mind what
you’re going to do with the food. Increasing interest in feeding strategies aimed to influence the fate of food.
§ Digestion and absorption
§ Storage (TAGs in adipose tissues, glycogen in muscles and liver)
§ Utilisation (used and oxidized, or proteins converted into carbs and vice versa)
1. Digestion <-> Fermentation
Microbial fermentation may provide energy but NO amino acids
Meal is coming in the GI tract à bolus is broken down in smaller particles (macromolecules)
With the addition of enzymes and lots of water, ions and bile acids (for lipids): we get monomers/oligomers
which can be absorbed à transported in the blood to the body where it can be used for energy or stored
2. Enzymes lower the activation energy (e.g. proteolytic enzymes)
In non-enzymic reaction: lots of energy is needed/should be invested to get the final product (requires extreme
conditions and lots of energy is needed)
With enzymes: we only need a fraction of the required energy to reach the final product and lower
temperature: one enzyme with specific amino acids: very specific and target one specific reaction
à proteolytic enzymes make sure specific bonds are hydrolysed by lowering activation energy of proteolysis
3. Why does the digestive system doesn’t digest itself?
• The activity of enzymes is restricted to presence of food. E.g. no release of enzymes when you’re
sleeping à regulation (locally, distal, proximal) when the food is there or not
• Pro-enzymes (= zymogens = not activated yet): not functional yet, so they are in the cells available to
digest food components.
• Mucus = protective layer/barrier coating the walls to avoid digestion of the walls by the enzymes
• High replacement rate (turnover) of mucosal cells lining the intestine
à all these have an influence on metabolic settings: how well are you digesting food and energy
Settings of metabolism
We start with digestion and absorption of monomers after having eaten the food
, I. Intermediary metabolism: metabolism at cellular level (biochem.) = SUBSTRATE METABOLISM
§ interconversions of absorbed monomers e.g. how are you converting glucose into specific amino acids,
or backbone of TAG can be used to synthesize glucose
§ anabolic reactions (build-up of TAG or glycogen storage, protein metabolism) à synthesis of body
constituents
§ catabolic reactions (energy/ ATP/ heat): release of energy from food or body constituents needed for
cellular metabolism
§ unavoidable waste products
Time scale of events: post-prandial (after you have eaten) vs post-absorptive (long enough after a meal when
nutrients are already absorbed – fasted)
Physiological adaptation à to maintain homeostasis
Settings of metabolism can be influenced by environmental conditions, nutritional input + physiological output
II. Meal feeding ~ metabolic changes
POST PRANDIAL PHASE (PP) POST ABSORPTIVE PHASE
Digestion – Absorption – Storage Utilisation
Input > Needs à ANABOLIC or CATABOLIC disposal Input < Needs à MOBILISATION
(Storage, interconversion, oxidation) (protein turnover, interconversion, oxidation)
Nutrients get stored or are used to make other kinds of Intestine doesn’t play a role anymore à mainly liver
molecules (% on needs) Made molecs are used and body will have other
needs, e.g. you need water because you’re thirsty
- glucose and a.a. absorbed in the guts They all contribute to convert into glucose to fuel the
- glucose transferred to the liver to be stored as glycogen brain
(amount % on glucose needs) - fatty acids are converted into ketone bodies
- a.a. transferred to the liver and are turned into proteins (muscles use ketone bodies to produce energy, to
in the liver have enough energy)
- TAGs in chylomicrons are stored in white adipose tissue - glycogen converted into glucose (organs can use
(transporter by the portal vein) glucose for energy production)
- glucose transferred to organs needing glucose, through - muscles provide a.a. to other organs (e.g. liver and
the portal vein kidneys) to use for their energy production
- a.a. stored as proteins in muscles (muscle mass )
- glucose stored in muscles as glycogen
Thermogenic effects of a meal in PP - aka diet-induced Thermogenesis (DIT)
- Post-prandial metabolism (PPM) increases heat production (5-20% ingested metabolizable energy
(ME)) à if you don’t shield yourself, it is released in the environment
- Effects depend on ingested nutrients: proteins > carbs > fat à when you eat proteins, there are less
metabolites available for metabolism
- ingested ME is not corrected for energetic costs of PPM
à always happening that we produce heat
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