D1 - Human Nutrition

Question 1

Nutrient

Answer 1

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

Question 2

Essential nutrients

Answer 2

cannot be synthesised by the body and must be ingested as part of the diet

Question 3

Non-essential nutrients

Answer 3

Non-essential nutrients can be made by the body or have a replacement nutrient which serves the same dietary purpose
Carbohydrates are not considered essential nutrients as human diets can obtain energy from other sources without ill effect

Question 4

Malnutrition

Answer 4

health condition caused by a deficiency, imbalance or excess of nutrients in the diet
It can be caused by an improper dietary intake of nutrients – e.g. overnutrition (too much) or undernutrition (not enough)
It can be caused by the inadequate utilisation of nutrients by the body – e.g. due to illness or disease

Question 5

Malnutrition symptoms

Answer 5

stunted growth and wasting (undernutrition), as well as obesity (over nutrition)

Question 6

Energy content

Answer 6

estimated by burning a sample of known mass and measuring the energy released via calorimetry
Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)

Question 7

Errors in calorimetry

Answer 7

biggest source of error in calorimetry is usually caused by the unwanted loss of heat to the surrounding environment
The food sources should be burnt at a constant distance from the water to ensure reliability of results
The initial temperature and volume of water should also be kept constant (1 g of water = 1 cm3 or 1 ml)

Question 8

Energy content - carbs

Answer 8

Carbohydrates are preferentially used as an energy source because they are easier to digest and transport

Question 9

Energy content - lipids

Answer 9

Lipids can store more energy per gram but are harder to digest and transport (hence are used for long-term storage)

Question 10

Energy content - proteins

Answer 10

Protein metabolism produces nitrogenous waste products which must be removed from cells

Question 11

Amino acids

Answer 11

20 different amino acids which are universal to all living organisms
Essential amino acids cannot be produced by the body and must be present in the diet
Non-essential amino acids can be produced by the body and are therefore not required as part of the diet
Conditionally non-essential amino acids can be produced by the body, but at rates lower than certain conditional requirements (e.g. during pregnancy or infancy) – they are essential at certain times only

Question 12

Phenylketonuria (PKU)

Answer 12

genetic condition that results in the impaired metabolism of the amino acid phenylalanine
It is an autosomal recessive disease caused by a mutation to the gene encoding the enzyme phenylalanine hydroxylase
Phenylalanine hydroxylase (PAH) normally converts excess phenylalanine within the body into tyrosine
In people with PKU, the excess phenylalanine is instead converted into phenylpyruvate (also known as phenylketone)
This results in a toxic build up of phenylketone in the blood and urine (hence phenylketonuria)
Untreated PKU can lead to brain damage and mental development issues, as well as other serious medical problems

Question 13

PKU diagnosis & treatment

Answer 13

Infants with PKU are normal at birth because the mother is able to break down phenylalanine during pregnancy
Diagnosis of PKU is made by a simple blood test for elevated phenylalanine levels shortly after birth
PKU is treated by enforcing a strict diet that restricts the intake of phenylalanine to prevent its build up within the body
This low-protein diet should include certain types of fruits, grains, vegetables and special formula milk
This diet should be supplemented with a medical formula that contains precise quantities of essential amino acids
Patients who are diagnosed early and maintain this strict diet can have a normal life span without damaging symptoms

Question 14

Lipids

Answer 14

Humans can synthesise most fatty acids from carbohydrates, but two (cis)-polyunsaturated fatty acids are considered essential
Alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) cannot be synthesised by the body
This is because humans lack the enzyme required to introduce double bonds at the required position of the carbon chain
Essential fatty acids are modified by the body to make important lipid-based compounds (such as signalling molecules)
There is evidence to suggest dietary deficiencies of these fatty acids may be linked to impaired brain development (e.g. depression) and altered maintenance of cardiac tissue (e.g. abnormal heart function) – although this evidence is contested

Question 15

LDLs & HDLs

Answer 15

Low density lipoproteins (LDLs) carry cholesterol from the liver to the body (hence raise blood cholesterol levels)
High density lipoproteins (HDLs) carry excess cholesterol back to the liver for disposal (hence lower blood cholesterol levels)

Question 16

Cholesterol from diet

Answer 16

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

Question 17

Consequences of high cholesterol

Answer 17

High cholesterol levels in the bloodstream lead to the hardening and narrowing of arteries (atherosclerosis)

When there are high levels of LDL in the bloodstream, the LDL particles will form deposits in the walls of the arteries
The accumulation of fat within the arterial wall leads to the development of plaques which restrict blood flow
If coronary arteries become blocked, coronary heart disease (CHD) will result – this includes heart attacks and strokes

Question 18

Vitamins

Answer 18

Vitamins are organic molecules with complex chemical structures that are quite diverse and hence categorised by groups
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)
The functions of vitamins are as diverse as their structure, although many function as cofactors, antioxidants or hormones
Many vitamins are essential as they cannot be synthesised by the body and their absence may cause a deficiency disease

Question 19

Ascorbic acid

Answer 19

Ascorbic acid is a form of vitamin C that is required for a range of metabolic activities in all animals and plants
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
Ascorbic acid is made internally by most mammals from monosaccharides – but it is not produced by humans
Consequently, human must ingest vitamin C as part of their dietary requirements in order to avoid adverse health effects
A deficiency in vitamin C levels will lead to the development of scurvy and a general weakening of normal immune function
Common food sources of vitamin C include citrus fruits and orange juice

Question 20

Vitamin D

Answer 20

Vitamin D is involved in the absorption of calcium and phosphorus by the body – which contribute to bone mineralisation
In the absence of sufficient amounts of this vitamin, these elements are not absorbed but instead excreted in the faeces
This can lead to the onset of diseases such as osteomalacia (where bones soften) or rickets (where bones are deformed)
Vitamin D can be naturally synthesised by the body when a chemical precursor is exposed to UV light (i.e. sunlight)
The vitamin D may be stored by the liver for when levels are low (e.g. during winter when sun exposure is reduced)
Individuals with darker skin pigmentation produce vitamin D more slowly and hence require greater sun exposure
Vitamin D deficiencies are usually restricted to individuals with highly limited sun exposure (e.g. elderly, certain ethnicities)
While excess sun exposure is beneficial for vitamin D production, it also increases the risks of developing skin cancers

Question 21

Minerals

Answer 21

Dietary minerals are chemical elements required as essential nutrients by organisms
Minerals present in common organic molecules are not considered essential – e.g. C, H, O, N, S
Minerals include calcium (Ca), magnesium (Mg), iron (Fe), phosphorus (P), sodium (Na), potassium (K) and chlorine (Cl)

Question 22

Minerals - human development

Answer 22

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 23

Minerals - plant development

Answer 23

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 24

Appetite control - hormones

Answer 24

Appetite is 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)
The release of hormones can be triggered in a number of ways:
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 will either stimulate or inhibit the appetite control centre to promote sensations of hunger or satiety
Hormones that trigger a hunger response include ghrelin (from stomach) and glucagon (from pancreas)
Hormones that trigger a satiety response include leptin (from adipose tissue) and CCK (from intestine)
Hint: Ghrelin Grows Hunger ; Leptin Lowers Hunger

Question 25

Obesity

Answer 25

Clinical obesity (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 26

Obesity consequences

Answer 26

Individuals who are overweight or obese are more likely to suffer from hypertension (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)

Individuals who are overweight or obese are also more likely to suffer from type II diabetes (non-insulin dependent)

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

Question 27

Starvation

Answer 27

Starvation describes the 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
This leads to muscle loss (as muscle proteins are metabolised for food) and eventually organ damage (and death)

Question 28

Anorexia nervosa

Answer 28

Anorexia nervosa is an eating disorder in which individuals severely limit the amount of food they intake

It is most common in young females with body image anxiety and can potentially be fatal if left untreated

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

Question 29

Dietary Intake

Answer 29

The recommended daily intake for a nutrient (RDI) is the daily dietary level required to meet the requirements of health

It is an estimate only and will vary according to age, gender, activity levels and medical conditions

The recommendations are based on a daily energy intake of 8400 kJ (2000 kcal) for healthy adults

On food packages, this information is usually presented as a percentage of a daily total (based on identified serving size)