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Summary Nutritional Physiology (HAP30306)
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A summary of the course HAP30306 Nutritional Physiology.
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Nutritional PhysiologyLecture 1 Mass flow of nutrients (through the body and its cells)
Nutritional physiology – mass flow
- Nutritional input (what you eat, when you eat
it, how many meals, etc.)
o Total daily intake (kJ)
o Meal size, pattern
o Nutrient composition
- Physiological output (how much energy do you
need for your metabolism and your health
status, dependent on environment)
o Physiological status
o Health status
o Environment
- Metabolism
o ∆ Metabolic pathways
o ∆ Energetic efficiencies
o ∆ Body composition – waste products
Nutritional input and physiological output need to be in balance, if so you don’t gain weight or lose
weight. Metabolism makes this balance, which is constantly switching between your nutritional input
and physiological output in order to keep the balance.
Post prandial phase is where you deal with the incoming nutrients/the incoming energy. Post
absorptive phase is where you don’t have this, for example in the morning when you get up before
you have breakfast and your last meal was yesterday evening (diner), so you really rely on energy
from your body to fulfil your physiological output, because you need energy to remain alive. Thus,
metabolism is constantly switching for these different situations. Therefore, it can switch in
pathways, but also in energetic efficiencies (do you need to get more heat or do you need to get
more energy). This will switch accordingly. This might have ultimately an effect on the body
composition. True balancing aspects in nutritional input and physiological output.
Nutritional input can be anything, whatever you eat as long as there is energy in, the metabolism will
depend on it and will switch to it. For physiological output it is exactly the same. If you start sporting,
you need more energy for physiological output. Everyone needs energy to remain in the stages that
they are and moving, etc. But there is a difference between younger and older people.
Nutritional physiology
Dietary components – nutrients:
- Macronutrients (carbohydrates, proteins, fat)
- How do they move through the body?
o Translocation (translocated to different locations)
o Transformation (transformed/adapted, broken down in different structures →
monomers → absorbed in GI-tract)
- How are these movements regulated?
o Neural system
, o Endocrine system (hormonal)
- What are physiological options/benefits for the body?
- How do nutrients leave the body?
o CO2, thus oxidized → provides energy for your body
Human Digestive System
You start in the mouth (oral cavity), you swallow the food
through the oesophagus into the stomach and thereafter
it comes into the small intestine (duodenum, jejunum
and ileum). After the 5m long small intestine it comes
into the cecum and then into your colon (transverse,
ascending and descending colon). What is not digested
(or can’t be digested) at that point, is going to the rectum
and eventually to your anus and will be excreted.
What happens after eating?
- Hardly any influence on the fate of the food after
you swallow
o Digestion and absorption (converted)
o Storage (e.g. as triglyceride in adipose
tissue)
o Utilisation (directly used and oxidized)
- Increasing interest in feeding strategies aimed to
influence the fate of the food, but it is very hard because it also has to do with this balance:
Nutritional input ↔ Metabolism ↔ Physiological output
Digestion ↔ fermentation
The gastrointestinal tract (GI) assimilates nutrients from a meal. Microbial fermentation may provide
energy, but NO amino acids. In a way it resembles how a factory works. You have your meal coming
in and the bolus is being grinded to smaller particles, to macromolecules/micro molecules. Then via
the monomers and oligomers it is absorbed. It needs enzymes and lots of water, bile acids (for the
lipids) and ions. Then, after the uptake of nutrients and bile acids, via circulation it is transported to
all of the other cells in your body. There they can produce and be used for energy production. Or if
you have to much energy, it will be stored temporarily or on the long term. If you have a positive
energy balance constant over time, then it will be stored for a longer time.
Look at enzymes, why do we need the enzymes for digestion? Enzymes lower the activation energy.
If you don’t have enzymes and you want to break down a protein, you need extreme situations; 10-
,12 hours, 12 mol/L of gastric acid (HCI) at 105°C and then you break down the proteins at some
random bonds within the protein. This is a severe situation and lots of energy is needed to be able to
do this. Within contrast, if you make use of enzymes (designed for this fate) the energy needed is
much less (fraction of total energy is needed), shorter in time (1-2 hours), a lower temperature (37°C,
optimal for most enzymes in digesting processes) and you have specificity, 1 enzyme for specific
amino acids within protein sequences. It is highly dedicated and very well defined, it makes use of
enzymes in order to break down macromolecules (proteins).
Why the digestive system does not digest itself?
So if we have those enzymes in our GI tract/in our stomach/in our intestines, why don’t we break
down the system our selves? Since the enzymes are digesting everything that they can;
- Activity restricted to presence of food (no release of enzymes when you are sleeping)
- Regulation (local, distal, proximal)
- Enzymes stored as inactive pro-enzymes (zymogens), means that they are not functional
- Non-digestible mucus (layer in our intestines) that coats the walls
- High replacement rate (turnover) of mucosal cells (highest in the intestine)
All of the above have influence on metabolic settings.
Settings of metabolism
- We start with the digestion and absorption of monomers after you have eaten the food
- Then you have the intermediary metabolism (metabolism at cellular level - biochemically)
o Interconversions of absorbed monomers
o Anabolic reactions (e.g. protein metabolism), build up of products
▪ Synthesis of body constituents
o Catabolic reactions (release of energy/ATP/heat), breakdown of products
▪ Release of energy from food or body constituents
o Unavoidable waste products
- Time scale of events (post prandial vs. post absorptive)
- Physiological adaptation
, Intermediary cellular metabolism
What is absorbed is glucose, amino acids and glycerol and fatty acids. Those are the unique features
of our macronutrients. They can be stored, like glycogen in the case of carbohydrates or proteins for
the amino acids and neutral fat or the triglycerides. But you also see that there is interconnection.
Glucose is broken down to acetyl CoA, fuelling the TCA cycle (CAC cycle) which for instance excretes
CO2 and it produces carriers (energy carriers), which contributes to the oxidative phosphorylation,
that gives rise to ATP production (cellular energy). It is not only for glucose, also for amino acids
which can fuel it likewise, but via different pathways and also the break down of fatty acids does the
same. Schematically three macronutrients; blue = glucose, green = lipids (fatty acids) and red = amino
acids.
Meal feeding – metabolic changes
- POST PRANDIAL PHASE (Digestion – Absorption – Storage), after eating. You have an
enormous amount of energy coming into the body thus;
o INPUT is higher than NEEDS, you start using all the nutrients especially for ANABOLIC
situations or CATABOLIC DISPOSAL
▪ (Storage the excess of energy for times when you have no input of energy,
interconversion, oxidation to continuous fuel the body with energy)
- POST ABSORPTIVE PHASE (Utilisation):
o INPUT < NEEDS → MOBILISATION
▪ (Turnover, interconversion, oxidation)
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