Nutrition, Diet and Body Weight

Question 1

Define metabolism

Answer 1

Metabolism is the set of processes which derive energy and raw materials from food and use them to support repair, growth and activity of the tissues of the body to sustain life

Question 2

What is the difference between anabolism and catabolism

Answer 2

• Anabolic pathways - use energy and raw materials to make larger molecules for growth and maintenance
• Catabolic pathways - break down larger molecules to release energy in terms of reducing power (release H)

Question 3

Explain the functions of metabolism

Answer 3

○ Oxidative pathways - convert food into energy
○ Fuel storage and mobilisation pathways - allow fuel to be stored when not needed such as through glycogen
○ Biosynthetic pathways - produce basic building blocks for cells
○ Detoxification pathways - remove toxins

Question 4

Define energy

Answer 4

Energy is the capacity to do work

Question 5

Explain why the body needs energy

Answer 5

○ Biosynthetic work (anabolism) - synthesis of cellular components
○ Transport work
§ Maintenance of ion gradients
§ Nutrient uptake
○ Mechanical work - muscle contraction
○ Electrical work - nervous impulse conduction
○ Osmotic work - kidney

Question 6

Explain the biological role of ATP

Answer 6

• Gamma phosphate in ATP contains chemical bond energy to drive cellular processes
○ ATP is not stored, only molecules that can be broken down to produce ATP, including glycogen and fat
○ Energy released in exergonic reactions used to drive ADP + P -> ATP

Question 7

Explain the biological role of creatine

Answer 7

• Creatine phosphate - when ATP levels are high, ‘phosphate bond energy’ may be stored in phosphocreatine
○ Creatine + ATP Phosphocreatine + ADP (via creatine kinase enzyme)
○ Creatine phosphate provides immediate energy - energy rich molecules in muscle
○ Creatine kinase (enzyme) a marker for myocardial infarction
§ CK is released from cardiac myocytes when damaged in myocardial infarction
§ Appears in blood after a few hours
○ Creatinine is the breakdown product of creatine and phosphocreatine
§ Produced by a spontaneous reaction at a constant rate unless muscle is wasting
§ Excreted via kidneys

Question 8

Outline how creatinine is used as biological marker

Answer 8

§ Produced by a spontaneous reaction at a constant rate unless muscle is wasting
§ Excreted via kidneys
§ Creatinine excretion power 24h is proportional to muscle mass of the individual
□ Provides a measure of muscle mass
§ Creatinine concentration in urine is a marker of urine dilution
□ Can be used to estimate true urinary loss of many substances

Question 9

Describe the structure and categories of carbohydrates

Answer 9

○ Contain aldehyde, ketone and multiple OH groups
○ Monosaccharides - single sugar units (3-9 C-atoms)
§ Glucose, fructose, galactose
○ Disaccharides - (2-3 units)
§ Maltose (glucose + glucose), sucrose (glucose + fructose), lactose (glucose + galactose)
○ Oligosaccharide - (3-12 units)
§ Dextrins - from digestion of starch using amylase
○ Polysaccharides - (10-1000’s units)
§ Starch, glycogen, cellulose - all glucose monosaccharide monomers
§ Cellulose cannot be broken in humans as we don’t contain enzymes to break ß-1,4-glycosidic bonds between glucose

Question 10

What are essential amino acids and list them

Answer 10

○ 9 ‘essential amino acids’ cannot be synthesised and must be obtained from diet
○ Isoleucine, lysine, threonine, histidine, leucine, methionine, phenylalanine, tryptophan, valine
If Learnt This Huge List May Prove Truly Valuable

Question 11

What are examples of essential fatty acids

Answer 11

Linolenic and linoleic acids

Question 12

Describe the structure of lipids within the body

Answer 12

Lipid composed of triacylglycerols (3 fatty acids esterified to one glycerol)
○ Saturated fatty acids contain no double bonds
○ Trans fats synthesised industrially to give favourable characteristics such as increased shelf life

Question 13

Explain the biological role of minerals

Answer 13

○ Electrolytes establish ion gradients across membranes & maintain water balance
§ Sodium, potassium, chloride
○ Calcium and phosphorus essential for structure (bones and teeth)
○ Calcium also very important signalling molecule
○ Enzyme cofactors (iron, magnesium, cobalt, copper, zinc, molybdenum)

Question 14

List the fat soluble vitamins and its associated deficiency diseases

Answer 14

A - Xerophthalmia (fail to produce tears)
D - Rickets
E - Neurologic abnormalities
K - Defective blood clotting

Question 15

State the associated deficiency diseases of some water soluble vitamins

Answer 15

B1 - Beriberi
B12 - anaemia
B6 - anaemia
C - survy
Folate - anaemia 
Niacin (B3) - pellagra

Question 16

State the role of dietary fibre

Answer 16

○ Found in cereal foods - cellulose, lignin, pectins, gums
○ Cannot be broken down by human digestive enzymes but essential for normal functioning of GI tract
§ Humans do not produce enzymes to break beta-1,4 glycosidic linkages in cellulose
○ Low fibre intake associated with constipation and bowel cancer
○ High fibre diet shows to reduce cholesterol and risk of diabetes
§ Cholesterol produces bile salts but fibre suppresses bile salts and excretes it so it cannot be recycled

Question 17

Give the equation for daily expenditure value

Answer 17

○ Daily energy expenditure = basal metabolic rate + diet induced thermogenesis (energy required to process food) + physical activity level

Question 18

How can the components of daily expenditure value be estimated

Answer 18

§ For individuals who are not obese, BMR = 100 x weight in kg
§ Physical activity level = BMR + (30% to 100% of BMR) depending on level of exercise
§ Diet induced thermogenesis ~10% of energy content of ingested food

Question 19

What are dietary reference values

Answer 19

• Dietary reference values are a series of estimates of the amount of energy and nutrients needed by different groups of healthy UK population

Question 20

State the amount of energy obtained from carbohydrates, fats, alcohol and protein

Answer 20

Fat - 37 kJ/g
Carbohydrates - 17 kJ/g
Protein - 17 kJ/g
Alcohol - 29 kJ/g

Question 21

List the essential components of the human diet

Answer 21

Protein, Fat, Carbohydrates, Minerals, Vitamins, Dietary fibre, Water

Question 22

Define obesity

Answer 22

• Obesity is the excessive fat accumulation in adipose tissue which impairs health
• Usually measured using body mass index > 30

Question 23

Give the BMI equation

Answer 23

• BMI = weight/height^2

○ Units are kg/m^2

Question 24

Interpret BMI values

Answer 24

<18.5 = underweight 
18.5 - 24.9 = desired weight
25 - 29.9 = overweight
30 - 34.9 = obese
>35 = severely obese

Question 25

What are the consequences of malnourishment

Answer 25

○ Longer hospital stays
○ Respond less well to treatment
○ 3 times more likely to develop complications after surgery
○ Higher mortality rates

Question 26

Describe appearance of marasmus

Answer 26

• Marasmus - protein energy malnutrition most commonly seen in children under 5
○ Looks emaciated with signs of muscle wasting, loss of body fat, no oedema
○ Hair is thin and dry, diarrhoea common, anaemia

Question 27

Describe appearance and pathophysiology of kwashiokor

Answer 27

Young child displaced from breastfeeding and fed a diet with some carbohydrate but low protein
○ Apathetic, lethargic, anorexic
○ Oedema, hepatomegaly, ascites (fluid in peritoneal cavity)
○ Low serum albumin (not enough amino acids to make), anaemia
○ Decrease plasma oncotic pressure - increase flow of fluid into interstitium = oedema

Question 28

Explain the roles of redox reactions and H-carrier molecules in metabolism

Answer 28

• Chemical bond energy of fuel molecules is released by oxidation reactions
• All oxidation reactions accompanied by a reduction reaction
○ Reducing power is converted to energy currency (ATP) by oxidative phosphorylation
• H-carrier molecules - when fuel molecules are oxidised, electrons and protons are transferred to carrier molecules
○ Eg. Oxidised form: NAD, reduced form: NADH + H+
○ Can be converted to oxidised form for energy

Question 29

Explain the roles of high- and low-energy signals in the regulation of metabolism

Answer 29

• When ATP concentration is high, anabolic pathways are activated and most molecules are in reduced form
○ Other high energy signals are NADH, NADPH, FAD2H
• When ATP concentration is low and ADP and AMP is high, catabolic pathways are activated
○ Adenylate kinase (myokinase): 2ADP -> ATP + AMP (AMP = low energy signal)
• When supply exceeds demand, energy is most often stored in the form of polymer macromolecules of fuel molecules
○ Eg. Glycogen, triglyceride
• Cell types that need to increase metabolic activity very quickly (skeletal muscles) need a reserve of high energy stores that can be used immediately (creating phosphate)