Nutrition, Diet and Energy Metabolism

Why do we need indigestible material in our diet?

For the normal functioning of the gastrointestinal tract E.g fibre

State the 3 main fuels of the body

Carbohydrates, fat and protein

Where are these fuels digested and absorbed?

In the gastrointestinal tract

What happens to the fuel not needed?

Fat is stored as adipose tissue
Carbohydrates turn to glucose then glycogen to be stored in muscles and liver

5 things we need energy for

Biosynthetic work - synthesis of cells

Electrical work - nervous system

Mechanical work - muscles

Transport - across membranes e.g sodium potassium pump

Osmotic - kidneys

Give an example of mechanical work

Cross bridges of actin and myosin requires hydrolysed ATP

BEMTO

B- biosynthetic

E- electrical

M - mechanical

T - transport

O - osmotic

What is chemical bond energy?

The potential energy found/ stored in chemical bonds

Describe what happens in an organic reaction to release energy

Covalent bonds are split by an input of energy. The free ions recombine and release energy

What is an exergonic reaction?

Energy released \> energy input

What is an endergonic reaction?

Energy input \> energy released

Where is the energy in ATP found?

In the phosphodiester bonds between beta and gamma phosphate of ATP

How is chemical bond energy in fuel molecules released?

Through oxidation reactions

What is the average daily expenditure for a 70kg male?

12,500 kJ

100 x weight (kg)

BMR calculation for someone NOT obese

4 major tissues contributing to BMR and percentages

\
Skeletal - 30% \n Central nervous system - 20% \n Liver - 20% \n Heart - 10%

5 factors affecting BMR

GEEBB

G- gender

E - environmental temperature

E - endocrine status

B - body size

B - body temperature

Why do males have a higher BMR than women?

Women have more adipose tissue which is less metabolically active than muscle

What is the BMR controlled by?

Thyroid hormones

3 factors of daily energy expenditure

BMR , voluntary exercise, diet induced thermogenesis

What is diet induced thermogenesis?

Energy needed to process the food (digest and absorb) through the gastrointestinal tract

Why is energy required for DIT?

DADS

D- digest

A - absurd

D- distribute

S - store

DADS

Disgust, absorb, distribute, store

What physiological problems are associated with saturated fats?

High blood cholesterol and heart disease

Why is there no requirement for glucose in the diet?

The body can synthesis it

Describe 2 ways the body can synthesise glucose

Gluconeogensis - amino acids and glycerol into glucose

Glycerol released from hydrolysis of fat

Why are fats important in the diet?

2\.2 x more energy than carbohydrates
Absorption of fat

soluble molecules

Some polyunsaturated fats not synthesised by the body

Name 4 fat soluble vitamins

A, D, E, K

What two groups can carbohydrates contain?

Aldehyde (C\=0H)
Keto (C\=0)

Give the general formula for carbohydrates

(CH20)n

Polypeptide with beta 1 4 glycosidic bonds

cellulose

What is fat (a lipid) composed of?

Triacylglycerols (3 fatty acids and one glycerol)

Why does fat yield more energy?

Less oxygen so it is more reduced, meaning it yields more energy when oxidised

Fats that contain a double bond between carbon

Unsaturated

How do excess amino acids help produce energy?

Use the carbon skeleton to feed into biochemical pathways

How many essential amino acids come from the diet?

9

Why does the body need protein/

Synthesis of essential amino acids

Why do we need extra protein in our diet?

although most amino acids released during breakdown are resynthesised in the liver, protein is lost by further degredation so need to replace it in the diet

Where does nitrogen go from degraded AA?

Excreted as urea

What is positive nitrogen balance?

Nitrogen intake \> nitrogen loss

Who might have a positive nitrogen balance?

Pregnant women - nitrogen associated with tissue repair and growth etc

When will nitrogen balance be negative?

During periods of starvation

What is the average water loss during the day? How?

2.5L
1.5L from urine, also through skin and expired air

How is water produced?

Mostly through cellular metabolism, but we make up the rest by drinking water

How does a high fibre diet reduce blood cholesterol?

1. Bile salts are recycled in the liver
2. Fibre can bind to bile salts (synthesised from cholesterol) in the GI tract
3. This means the liver no longer has enough
4. The liver pulls bile salts from the blood steam, lowering blood cholesterol

What is hypervitaminosis and how can it occur?

Excess vitamin intake which can lead to death e.g by people taking supplements

State the ranges of the BMI chart

1. Underweight =

What is increasingly replacing BMI? Give the numbers

Waist to hip ratio
Obese female \>0.85
Obese male \>0.9

Give 2 factors that may influence tendency to put on weight

Genetic, endocrine disorders

Body cells no longer respond to insulin produced by pancreas

Type 2

Excessive fat accumulation on adipose tissue which impairs health

Obesity

Is it better or worse to have a higher proportion of fat on upper body? Why?

Worse... increased risk of insulin resistance, hypertension, hyperlipidoemia

Hyperlipidoemia

Too many fats/lipids in blood

Do glycogen stores contain more water or fat?

Water

Why is there a rapid initial weight loss when you starve yourself?

Starvation is associated with reduction in liver glycogen stores that provide glucose to the brain. The glycogen stores contain more water than fat so weight is lost easily.
Weight loss then slows as these stores are used up

How does starvation lead to dehydration?

The liver behinds to convert fatty acids to ketone bodies to be used as fuel for the CNS but they disturb the blood PH and lead to dehydration

How can malnutrition effect patients?

They respond less well to treatment and x2 more likely to have complications are surgery... higher mortality rates

Give 2 malabsorption conditions

Coeliac and crohn's

State the 2 forms of protein energy malnutrition

Marasmus, Kwashiorkor

State three symptoms of marasmus

Muscle wasting, thin and dry hair , anaemia

When does kwashiorkor most commonly occur?

If the child is displaced from breastfeeding

Enlarged liver

Hepatomegaly

3 symptoms of kwashiorkor

\- child is lethargic and anorexic

\-generalised oedema or pitted oedema

-distended abdomen due to hepatomegaly

Why does kwashiorkor lead to oedemas?

There are insufficient amino acids for normal levels of blood protein - decreasing plasma protein pressure \n Leads to increase in flow of fluid to interstitial resulting in oedema

Albumin

Blood protein to maintain oncotic pressure

What will rapid refeeding result in?

Refeeding syndrome

When can refeeding syndrome occur?

When nutritional support is given too quickly to severely malnourished patients

Why can refeeding syndrome lead to electrolyte abnormalities?

The rapid refeeding increases blood and glucose levels, resulting in protein, fat and glycogen synthesis.
These processes use nutrient stores that are already depleted, resulting in electrolyte abnormalities

Give 3 transformations nutrients go through on the way to body tissues

\-degredation (decay) to release energy

\-storage in liver, adipose, skeletal muscle \n -inter conversion to other nutrients

Highly integrated network of chemical reactions that occur within cells

Cell metabolism

Why do cells need to metabolise nutrients?

Energy for cell function and synthesis
Biosynthetic reducing power for synthesis of cell components

Catabolism

Breakdown or larger molecules into smaller ones with the release of energy

Anabolism

Smaller molecules built into larger ones, requiring energy

Are anabolic pathways oxidative?

No, catabolic pathways are oxidative

What are anabolic pathways mainly for?

To drive the synthesis of cell components using intermediary metabolites produced in catabolic pathway

What do catabolic pathways produce?

Large amounts of free energy and intermediary metabolites

How do cells release energy from fuel molecules?

oxidation reactions - removal of e- of H+

What happens to the removed H atoms after oxidation?

Transferred to carried molecules

Give 3 examples of carrier molecules in their oxidised form

NAD, NADP , FAD

Why does the total concentration of reduced and oxidised carrier molecules have to be kept constant?

If all NAD+ were in reduced form NADH+, all oxidation reactions that require NAD+ could not occur

Reactions that release energy

Exergonic

Which reaction can occur spontaneously?

Exergonic reactions

Endergonic reactions

Reactions that require energy

What is the enthalpy change (deltaH) of an exergonic reaction?

Negative change (-deltaH)

What does the enthalpy change tell us?

The difference in energy between products and reactants

What is entropy (deltaS)?

Measure of disorder of products relative to reactants

What does it mean if deltaS is positive?

There is an increase in disorder

Describe what free energy is

Energy released in an exergonic reaction available to do work (deltaG)

When can a spontaneous reaction occur in terms of G?

When deltaG is negative as it means free energy is available

What equation links free energy, entropy and enthalpy?

deltaG = deltaH - TdeltaS

\
T = temp in kelvin (+273)

Where is energy conserved during catabolism of fuel molecules for synthesis of ATP? When is this released?

Covalent bond between terminal phosphate and fuel molecule

 released during hydrolysis when phosphate group is removed

What is ATP rapidly resynthesised from?

From ADP using free energy from catabolism of fuel molecules

When are catabolic pathways activated?

When concentration of ATP falls and ADP rises

Which pathways is activated when concentration of ATP rises?

Anabolic

State the reversible reaction for creatine phosphate

Creative + ATP —\> creatine phosphate + ADP

How is creatine phosphate helpful when ATP levels are low?

Can act as a small energy store and react with ADP to make ATP

How is creatinine produced?

When creatine and creatine phosphate undergo non enzymatic chemical changes

How is creatinine produced?

spontaneous breakdown of creatine

or

spontaenous breakdown of phosphocreatine

What are the calculations when deciding IV drip concentration for electrolytes and water?

Na+ , K+, Cl 1mmol/kg/day each \n Water: 30ml/kg/day

How much food does the average adult eat over a year?

500kg