Human Nutrition

Question 1

nutrient

Answer 1

chemical substance found in foods that is used in human body (carbohydrates, proteins, lipids, vitamins, minerals, and water)

Question 2

essential nutrients

Answer 2

those that cannot be synthesized by the body and must be ingested as part of the diet. carbs are not considered essential as human diets can obtain energy from other sources without effect

Question 3

malnutrition

Answer 3

health condition caused by deficiency, imbalance, or excess of nutrients in diet

Question 4

determining energy content

Answer 4

can be estimated by burning a sample of known mass and measuring the energy released via calorimetry
- Combustion of the food source causes the stored energy to be released as heat, which raises the temperature of water
- The amount of energy required to raise 1 g of water by 1ºC is 4.18 J – this is the specific heat capacity of water
Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)

Question 5

comparing energy content

Answer 5

• carbs are used as an energy source because they are easier to digest and transport (1,760 kJ per 100 g)
• lipids can store more energy per gram but are harder to digest and transport (4,000 kJ per 100 g)
• protein metabolism produces nitrogenous waste products which must be removed by cells (1,720 kJ per 100g)

Question 6

phenylketonuria (PKU)

Answer 6

genetic condition that results in the impaired metabolism of the amino acid phenylalanine
- autosomal recessive disease caused by a mutation to the gene encoding the enzyme phenylalanine hydroxylase (PAH)
- PAH normally converts excess phenylalanine within the body into tyrosine
- In people with PKU, the excess phenylalanine is instead converted into phenylpyruvate
- results in a toxic build up of phenylketone in the blood and urine
Untreated PKU can lead to brain damage and mental retardation, as well as other serious medical problems. PKU is treated by enforcing a strict diet that restricts the intake of phenylalanine to prevent its build up within the body.

Question 7

essential cis-polyunsaturated fatty acids

Answer 7

• Alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) cannot be synthesized by the body
• This is because humans lack the enzyme required to introduce double bonds at the required position of the carbon chain
• Foods rich in essential fatty acids (omega-3 and omega-6) include fish, leafy vegetables and walnuts

Question 8

low density lipoproteins (LDL)

Answer 8

carry cholesterol from liver to body (hence raise blood cholesterol levels)

Question 9

high density lipoproteins (HDL)

Answer 9

carry excess cholesterol back to liver for disposal (lower blood cholesterol levels)

Question 10

influence of fatty acids consumed

Answer 10

• Saturated fats increase LDL levels within the body, raising blood cholesterol levels
• Trans fats increase LDL levels and lower HDL levels, significantly raising blood cholesterol levels
• Cis-polyunsaturated fats raise HDL levels, lowering blood cholesterol levels
  Can lead to hardening and narrowing of arteries

Question 11

vitamins

Answer 11

organic molecules with complex chemical structures that are diverse
- Water soluble vitamins need to be constantly consumed as any excess is lost in urine (e.g. vitamins B, C)
- Fat soluble vitamins can be stored within the body (e.g. vitamins A, D, E, K)

Question 12

ascorbic acid

Answer 12

form of vitamin C
- In mammals it functions as a potent antioxidant and also plays an important role in immune function
- It is also involved in the synthesis of collagen (a structural protein) and in the synthesis of lipoproteins
- made in mammals but not in humans
- deficiency of vitamin C will lead to development of scurvy and general weakening of normal immune function

Question 13

Scurvy

Answer 13

deficiency disease
- skin discolouration and bruising
- hemorrhaging
- anaemia
- dental issues
- exhaustion
- swelling of joints

Question 14

vitamin D

Answer 14

involved in absorption of calcium and phosphorus in the body. vitamin D can be naturally synthesized by the body when a chemical precursor is exposed to UV light. The vitamin D may be stored by the liver for when levels are low.

Question 15

dietary minerals

Answer 15

chemical elements required as essential nutrients by organisms. Minerals include calcium (Ca), magnesium (Mg), iron (Fe), phosphorus (P), sodium (Na), potassium (K) and chlorine (Cl).
- Major constituents of structures such as teeth and bones (e.g. Ca, P, Mg)
- Important components of body fluids (e.g. Na, K, Cl)
- Cofactors for specific enzymes or components of proteins and hormones (e.g. Fe, P, I)

Question 16

minerals in plant development

Answer 16

• Magnesium is an important component of chlorophyll (required for photosynthesis)
• Potassium is an inorganic salt found within the sap of a plant (maintains water potential)
• Calcium is important for plant root and shoot elongation

Question 17

appetite

Answer 17

controlled by hormones produced in the pancreas, stomach, intestines and adipose tissue. - These hormones send messages to the appetite control centre of the brain (within the hypothalamus)
- Hormonal signals will either trigger a feeling of hunger (promote feasting) or satiety (promote fasting)

Question 18

hormones triggering appetite

Answer 18

• Stretch receptors in the stomach and intestine become activated when ingested food distends these organs
• Adipose tissue releases hormones in response to fat storage
• The pancreas will release hormones in response to changes in blood sugar concentrations
• Hormones that trigger a hunger response include ghrelin (from stomach) and glucagon (from pancreas) GROW HUNGER
• Hormones that trigger a satiety response include leptin (from adipose tissue) and CCK (from intestine) LOWER HUNGER

Question 19

obesity

Answer 19

(BMI > 30) describes a significant excess in body fat and is caused by a combination of two factors:
- Increased energy intake (i.e. overeating or an increased reliance on diets rich in fats and sugars)
- Decreased energy expenditure (i.e. less exercise resulting from an increasingly sedentary lifestyle)

Question 20

hypertension

Answer 20

abnormally high blood pressure
- Excess weight places more strain on the heart to pump blood, leading to a faster heart rate and higher blood pressure
- High cholesterol diets will lead to atherosclerosis, narrowing the blood vessels which contributes to raised blood pressure
- Hypertension is a common precursor to the development of coronary heart disease (CHD)

Question 21

type II diabetes

Answer 21

non-insulin dependent
- occurs when fat, liver and muscle cells become unresponsive to insulin (insulin insensitivity)
- results from a diet rich in sugars causing the progressive overstimulation of these cells by insulin
- overweight individuals who have a high sugar intake are more likely to develop type II diabetes

Question 22

starvation

Answer 22

severe restriction of daily energy intake, leading to a significant loss of weight
- As the body is not receiving a sufficient energy supply from the diet, body tissue is broken down as an energy source
- leads to muscle loss (as muscle proteins are metabolised for food) and eventually organ damage (and death)

Question 23

anorexia nervosa

Answer 23

an eating disorder in which individuals severely limit the amount of food they intake
- In severe anorexia, the body begins to break down heart muscle, making heart disease the most common cause of death
- Blood flow is reduced and blood pressure may drop as heart tissue begins to starve
- The heart may also develop dangerous arrhythmias and become physically diminished in size