Download The physiology of nutrition

The physiology of
nutrition
The aim of eating:
To provide raw materials and energy
sources for the body
The amount of energy stored in various organs (kJ)
Source of E
Blood Liver Brain Muscle
Fat
Glucose/Glycogen
252
1,638
34
5,040
336
Triglycerides
198
1,890
0
1,890
567,000
0
1,638
0
100,800
155
Proteins that can be
mobilised
Energy balance:
calory intake = calory output
if +: increased storage
if -: utilisation of stores
Nutrients:
Everything serving as raw material and
energy, plus all other molecules required
for their utilisation (trace elements, water,
ions and vitamins).
Bioactive substances: in the absence of these, the metabolic
processes would proceed towards undesired directions, and
diseases would develop (e.g. dietary fibres, flavonoids, etc.).
The well-balanced diet
• Isodynamic diet; applicable with certain restrictions only,
because:
– Loss of amino acids
– Fat soluble vitamines
– The digesting and absorbing capacities of the GI tract
• Recommendation for a healthy adult - The total amount of
energy consumed should have the following composition:
– Fats: < 30%
– Proteins: 10-15%
– Carbohydrates: > 55%
Nutrient Molecules (1)
Water, Inorganic salts
Carbohydrates
• Direct or indirect sources of energy
• When bound to proteins (glycoproteins): structural function
– Surface antigens, protective molecules (mucin), most of the
enzymes, globular proteins in the plasma, connective tissue
• Can be converted to other, biologically important molecules
• Dietary fibres:
– Water soluble (e.g. pektin)
– Water insoluble (e.g. cellulose, hemicellulose, lignin)
• Recommendation: 55-60% of the total energy uptake should be
provided by carbohydrates. The energy uptake ensured by the ”added
sugar” should be less than 10%. The recommended amount of dietary
fibres is 30 g/day (about 0.5-1 kg fresh vegetables and fruits; or
consumption of 56-84 g oat meal).
Functions of the dietary fibres (1)
• They delay the absorption of glucose, which
increases the sensitivity to insulin – the increase of
the blood glucose level is less pronounced after
meals
• They reduce the blood cholesterol levels
– Consumption of 5-6 g water soluble dietary fibres/day
may reduce it by 5-10%;
– If the plasma cholesterol level is reduced by 1% in the
population, it causes a 2% reduction of the mortality of
coronary diseases!!!
Functions of the dietary fibres (2)
• How plasma cholesterol level is reduced?
– The dietary fibres adsorb the cholesterol that is secreted
into the GI tract
– They make lipid absorbtion more difficult from the GI
tract
– The short-chained fatty acids produced from the dietary
fibres inhibit cholesterol production of the body
• Dietary fibres have important roles in weightcontrol as well as in reducing the incidence of
colon cancers
Nutrient Molecules (2)
Lipids
concentrated energy stores
a structural elements of membranes and certain other
organelles
Essential fatty acids: linolenic and linoleic acid they are the sources of the eicosanoids (containing 20
and 20+ carbon atoms)
Recommendation
• Lipids should provide less than 30% of the daily total
energy intake.
• At most 10% of the daily energy intake should be provided
by saturated fatty acids.
• The daily cholesterol uptake should be less than 600 mg
with normal and less than 300 mg with elevated plasma
cholesterol levels.
Nutrient Molecules (3)
Proteins and amino acids
Essential components of the tissues and enzymes,
(enzymes, transport and storage proteins, structural proteins, protective proteins,
hormones, contractile proteins, proteins with not fully known functions)
may serve as energy sources
• N-balance
• Surplus: becomes energy source,
protein synthesis is regulated by
hormones
Essential amino acids (Threonine, Methionine, Valine, Isoleucine,
Tryptophan, Phenylalanine, Lysine, Leucine, Histidine [in infants only],
Tyrosine {can be synthesized from Phenylalanine})
Nitrogen balance
• This is when a person’s daily intake of
nitrogen from proteins equals the daily
excretion of nitrogen
• If +: The protein content of the body
increases
• If -: The protein content of the body
reduces
Biological value of the dietary
proteins
• The proportion of proteins that can be utilised for
the biosynthesis of the „own” proteins after
absorbtion. Eg.:
–
–
–
–
–
–
Mother milk, whole egg: 100
Cow milk: 88-95
Beef: 88-92
Fish: 80-92
Soya beans: 74-78
Corn flour: 49
Recommended daily protein
intake
• Healthy, adults, on mixed diet: 0.8 g/kg
– In the case of 100 kg body mass: 80 g/day
•
•
•
•
Premature babies: 3.8 g/kg (mother milk must be supplemented with proteins)
Infants: 2.2 g/kg
60+ : 0.9-1.1 g/kg (decreased bioavailability)
Pregnant and lactating women: 0.8 g/kg
– +10 g (pregnancy)
– +20 g (at the beginning of the lactation)
– +15 g (later phase of lactation)
Nutrient Molecules (4)
Vitamins:
• they are required in small quantities
• they are available in the food or provided by bacteria of
the gut
• they do not give energy but they act as cofactors or
enzymes
• characteristic deficiency symptoms are seen
• these symptoms can be treated by the application of the
appropriate vitamin
Fat soluble vitamins (1)
Deficiencies
Vitamin A (Retinol)
Formation of visual pigments
maintenance of epithelial structures
appropriate fetal development
Hemeralopia (night blindness)
Skin lesions (xerophthalmia)
Birth defects
Vitamin D (Calciferol)
Enhancement of Ca2+ and phosphate
absorption from gut
Bone and tooth formation
Rickets in children
(defective bone formation)
Osteomalacia in adults
Fat soluble vitamins (2)
Deficiencies
Vitamin E (Tocopherol)
Maintenance of RBCs, antioxidant
Increased fragility of RBCs
Muscular dystrophies
Abortion
Vitamin K (Naphtoquinone)
Enables vitamin K-dependent
clotting factor synthesis in liver
Failure of blood coagulation
Water soluble vitamins (1)
Deficiency
Vitamin B1 (Thiamine)
It is a co-carboxylase, needed for the
proper activity of the proteindecarboxylase (thus for decarboxylation
- Kreb’s cycle)
Beriberi
Stoppage of CHO metabolism at
pyruvate
neuritis (kakke)
heart failure (shoshin)
• Casimir Funk discovered that the extract of the rice polish cures
pigeons suffering from beriberi
• He was convinced that he discovered a new class of amines essential
for life (vital amines), and the term yielded the now accepted term:
vitamine
1929: Nobel prise for the discovery of the „antineurotic vitamine” to Christiaan Eijkman
In 40% of the chronic alcoholics vitamin B1 deficiency persists (polyneuropathy);
3-10% of this has the cerebral manifestation (Wernicke encephalopathy).
Water soluble vitamins (2)
Deficiencies
Vitamin B2 (Riboflavin)
Flavoproteins in oxidative phosphorylation
Fissuring of the skin
Glossitis, cheilosis
Vitamin B6 (Pyridoxine)
Coenzyme for amino acid and fatty acid
metabolism
Dermatitis
Nervous disorders
Vitamin B3 (Niacin,
Nicotinic acid and nicotinic acid amid)
Coenzyme in hydrogen transport
(NAD and NADP)
Pellagra (3D’s disease)
Dermatitis
Digestive
disturbances
Dementia
Water soluble vitamins (3)
Deficiencies
Vitamin B12 (Cyanocobalamin)
Nucleoprotein synthesis, RBC production
Pernicious anemia
Folic acid
Nucleoprotein synthesis, RBC production
Failure of RBCs to mature
“Fetus protecting vitamin”
Anemia
Vitamin B5 (Panthotenic acid)
Constituent of coenzyme A
Neuromotor disorders
Essential for the health of skin and hair
„Burning feet syndrome”
Water soluble vitamins (4)
Deficiencies
Biotin
Protein and fatty acid synthesis
Dermatitis
Transamination
Muscle pain
Vitamin C (Ascorbic acid)
Vital element for collagen synthesis
(Prolyl-hydroxylase)
Antioxidant
Scurvy
Infectious diseases of
the respiratory tract
Failure to form
connective tissue
Nutrient Molecules (5)
Trace elements:
(deficiency) (too much)
• they are required in minute quantities
• Iron (anemia)
(haemochromatosis)
• Cobalt (part of vitamin B12, pernicious anemia)
• Iodine (thyroid hormones, hypothyreosis)
• Zinc (dermal ulcers, reduced immune response)
• Copper (anemia, impared bone formation, plasma cholesterol level ↑)
(Wilson’s disease, brain damage)
• Chromium (insulin resistance)
• Fluoride (increased risk of caries)
Feeding centres:
Lateral portion of the hypothalamus feeding centre;
if stimulated: evokes eating behavior
if damaged: aphagia
Ventromedial portion of the hypothalamus satiety centre;
if stimulated: food intake stops
if damaged: hyperphagia and obesity
(glucostat)
Energetics
Important rules
Hess’s law
Van’t Hoff’s Law
Daily energy request (Total energy
expanditure – TEE)
• Basal metabolism – 60-75%
• Physical activity – 15-30%
• Specific dynamic action (DIT) – 5-10%
Energy sources:
CHO
Fat
Proteins
Energy yield/g in the
bomb calorimeter
17 kJ
40 kJ
24 kJ
17 kJ
CO2 + H2O
CHO
40 kJ
FAT
CO2 + H2O
24 kJ
Proteins
CO2 + H2O + NO2
Energy sources:
CHO
Fat
Proteins
Energy yield/g in the
body
17 kJ
40 kJ
17 kJ
Energy yield/g in the
bomb calorimeter
17 kJ
40 kJ
24 kJ
17 kJ
CO2 + H2O
CHO
40 kJ
FAT
CO2 + H2O
17 kJ
Proteins
7 kJ
CO2 + H2O + Urea
CO2 + H2O + NO2
TEE
• TEE = BMR + DIT + Energy expanditure of the muscle activity
– BMR: Basal metabolic rate
– DIT: Diet-induced thermogenesis
• BMR = TEE – DIT – Energy expanditure of the muscle activity
• BMR includes:
– Energy request of the biosynthesis
– Neuronal functions
– Maintaining skeletal muscle tone
– Circulatory and respiratory work
– Secretion activity of glands
– Energy request of homeostatic functions
– Energy request of thermoregulation
Basal Metabolic Rate (BMR)
Factors influencing BMR:
– sleep: -10%
– Cold temperature: +2-5%
– Body temperature: every 1ºC increase above 30ºC :
+0,5 - 13%
– Gender: it is less in women
– Age: it increases up to 4-5-years, than begins to reduce
(normalised to the body surface area)
MENTAL ACTIVITY HAS NO REAL INFLUENCE ON THE BMR
Determination:
Conditions:
Direct calorimetry
Indirect calorimetry
complete physical and mental rest…
Indirect technique
(Caloric equivalent of O2: ~ 20 kJ/L)
In a 70 kg person about 7100 kJ/day
Thyroid hormones and sympathetic activity
very effectively increase BMR.
Comparing BMR values
Normally: 155 – 175 kJ/h/m2
The thermic effect of eating
Diet-induced thermogenesis (DIT)
• The energy cost of
– Food absorption
– Food metabolism
– Storage
CHO:
Fat:
Proteins:
Mixed diet:
4-7%
2-4%
18-25%
8-15%
Respiratory Quotient (RQ)
RQ = CO2 produced /O2 consumed
Glucose
C6H12O6 + 6 O2 = 6 CO2 + 6 H2O + 38 ATP
6 CO2/6 O2 = 1
Palmitic acid
C16H32O2 + 23 O2 = 16 CO2 +16 H2O +129 ATP
16 CO2/23 O2 = 0.7
RQ values
RQproteins
RQmixed
RQbrain
RQstomach
=
=
=
=
0.8
0.82
0.98
negative
During exercise: RQ ( glycogen degradation) up to 2
When prolonged exercise: RQ ( fat combustion)
as low as 0.5
Metabolic acidosis RQ, alkalosis RQ
The „Body Mass Index” - BMI
• BMI = body weight (kg) / [body height (m)]2
– BMI < 16: Starvation
– 20 < BMI < 25: Physiological
– 25 < BMI < 30: Overweight
– 30 < BMI: Obese
Thermoregulation
The aim of thermoregulation:
to maintain a constant core temperature
by matching the amount of heat produced
with the amount of heat given away
Heat losing mechanisms
Direct
Indirect
Conduction
Respiration
Convection
Evaporation
Radiation
What determines direct heat loss?
Direct heat loss = k × S × (Tskin – Tenv)
Heat transfer coefficient
Surface area
Convection, conduction and radiation may work in both
directions (i.e. heat may be gained from the environment).
The significance of evaporation
(Sweating)
Evaporation can ONLY result in heat loss.
Evaporation is the ONLY WAY to lose heat
if Tenv > Tskin!!!!!
May be as much as 2 L/hr
Sweat glands have sympathetic cholinergic innervation
Heat producing mechanisms (1)
Shivering thermogenesis
(heat production may be 4-5-times higher than at rest!)
Shivering is a high frequency (10-20 Hz) skeletal muscle
contraction, when no effective work is performed.
Heat producing mechanisms (2)
Non-shivering thermogenesis:
Metabolism
(Sympathetic activity, thyroid hormones, glucocorticoids,
insulin, glucagon)
Exercise
Thermogenin in brown fat
(Capable of uncoupling the electron
transport chain from the process of making ATP. The result is the production of
heat instead of the ATP energy.
Thermogenesis occurring in the brown fat is increased by sympathetic activity
via β3 receptors)
Maintenance of the constant
core temperature
At external temperatures
of approximately
23 °C - 30°C
Vasomotor reactions
Above 30 °C
+ Evaporative reactions
Below 23 °C
+ Metabolic reactions ↑
The Big Boss is the hypothalamus
(centre of regulation)
SET POINT = 37 °C
Input from
Thermoreceptors
Hypothalamus
(Both core and shell)
Outputs to
skin circulation (vasomotor responses),
skeletal muscle (shivering, voluntary movements),
sweat glands,
metabolic changes (via Symp. NS, thyroid glands)
brown fat
How does the hypothalamus work?
(1)
Case 1.
Response
the core temperature is
higher than the set point
Heat producing mechanisms Voluntary movements Heat losing mechanisms Vasodilatation
Sweating
How does the hypothalamus work?
(2)
Case 2.
Response
the core temperature is
lower than the set point
Heat producing mechanisms Shivering
Metabolic activity Symp.activity, Thyroid hormons
Voluntary movements Heat losing mechanisms Vasoconstriction
Piloerection
Curling up
How does the fever develop?
NEW SET POINT = 40 °C (!)
Endogen pyrogens
Hypothalamus
(PGE2)
Exogen pyrogens
Heat producing mechanisms Heat losing mechanisms Vasoconstriction
Piloerection
Curling up
Shivering
Metabolic activity Sympathetic activity
Voluntary movements How is the fever terminated?
SET POINT = 37 °C (again)
Aspirin
Heat losing mechanisms Vasodilatation
Sweating
Hypothalamus
The comfort zone
Q*
Q
T
T
T
The very essence of
thermoregulation
Q*
Q
T
T