Human nutrition Flashcards
nutrient
a chemical substance found in foods that is used in the human body
classes of nutrients
carbohydrates, proteins, lipids, vitamins, minerals and water
essential nutrients
- cannot be synthesised by the body
- must be ingested as part of the diet
Non-essential nutrients
can be made by the body or have a replacement nutrient which serves the same dietary purpose
e.g. Carbohydrates are not considered essential nutrients as human diets can obtain energy from other sources without ill effect
causes of malnutrition
caused by an improper dietary intake of nutrients:
e.g. overnutrition (too much) or undernutrition (not enough)
caused by the inadequate utilisation of nutrients by the body – e.g. due to illness or disease
malnutrition
health condition caused by a deficiency, imbalance or excess of nutrients in the diet
symptoms of malnutrition
stunted growth (height too short regarding the age)
wasting (undernutrition)
obesity (over nutrition)
energy content of food
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
Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)
errors in calorimetry
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
comparing energy content
carbohydrates, lipids (fats) and proteins
Carbohydrates - preferentially used as an energy source because they are easier to digest and transport
Lipids- can store more energy per gram but are harder to digest and transport (hence are used for long-term storage)
Protein metabolism produces nitrogenous waste products which must be removed from cells
amino acids
20 in total
monomeric building blocks from which proteins are constructed
Lack of essential amino acids affects the production of proteins
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
phenylketonuria
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
Phenylalanine hydroxylase (PAH) normally converts excess phenylalanine within the body into tyrosine
In PKU patients, the excess phenylalanine is instead converted into phenylpyruvate (phenylketone)
result = a toxic build up of phenylketone in the blood and urine (phenylketonuria)
diagnosis of PKU
Untreated PKU can lead to brain damage and mental retardation
Infants with PKU are normal at birth because the mother is able to break down phenylalanine during pregnancy
Diagnosis is made by a simple blood test for elevated phenylalanine levels shortly after birth
treatment of PKU
enforced strict diet to restrict the intake of phenylalanine and prevent its build up within the body
low-protein diet
diet supplemented with a medical formula containing precise quantities of essential amino acids
essential (cis)-polyunsaturated fatty acid
Alpha-linolenic acid (an omega-3 fatty acid)
linoleic acid (an omega-6 fatty acid)
humans lack the enzyme required to introduce double bonds at the required position of the carbon chain
found in fish, leafy vegetables and walnuts
significance of fatty acids
modified by the body to make important lipid-based compounds (such as signalling molecules)
fatty acid deficiency may be linked to impaired brain development (e.g. depression) and altered maintenance of cardiac tissue (e.g. abnormal heart function)
Fats and cholesterol
cannot dissolve in the bloodstream, are packaged with proteins (to form lipoproteins) for transport
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)
fatty acids and cholesterol in the bloodstream
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
high cholesterol levels
harden and narrow arteries (atherosclerosis)
highgh levels of LDL = LDL particles 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
coronary arteries become blocked=coronary heart disease (CHD) + heart attacks and strokes
vitamins
chemically diverse carbon compounds that cannot be synthesised by the body
function as cofactors, antioxidants or hormones
absence may cause a deficiency disease
categories of vitamins
Water soluble vitamins, 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)
ascorbic acid
vitamin C
In mammals- functions as a potent antioxidant, plays an important role in immune function
involved in the synthesis of collagen (a structural protein), synthesis of lipoproteins
made internally by most mammals from monosaccharides, except humans
ascorbic acid deficiency
scurvy - a general weakening of normal immune function
Vitamin C deficiency symptoms
S kin discolouration, bruising H emorrhaging A naemia D ental issues E xhaustion S welling of joints
= S H A D E S
Vitamin D deficiency
In the absence vitamin D, Ca & P are not absorbed, but excreted in the faeces
affects bone mineralisation
causes :
rickets (deformation of bones)
osteomalacia (softening of bones)
vitamin D
involved in the absorption of calcium and phosphorus
contributes to bone mineralisation
stored by the liver for when levels are low
Individuals with darker skin pigmentation produce vitamin D more slowly and hence require greater sun exposure
Symptoms of Vitamin D Deficiency (Rickets)
B one fragility A trophy/ muscle weakening D dental problems G growth retardation E enlargement of liver S keletal deformities
= B A D G E S
minerals
chemical elements required as essential nutrients by organisms
essential – e.g. C, H, O, N, S
deficiency= disorder
functions of minerals
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)
minerals and plant development
Magnesium - component of chlorophyll (required for photosynthesis)
Potassium -an inorganic salt found within the sap of a plant (maintains water potential)
Calcium - important for plant root and shoot elongation
appetite control
situated in the centre of hypothalamus
controlled by hormones produced in the pancreas, stomach, intestines and adipose tissue
hormones send messages to the appetite control centre of the brain (within the hypothalamus)
Hormonal signals either trigger a feeling of hunger (promote feasting) or satiety (promote fasting)
release of hormone
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 either stimulate or inhibit the appetite
trigger a hunger response: ghrelin (from stomach) and glucagon (from pancreas)
trigger a satiety response include leptin (from adipose tissue) and CCK (from intestine)
Hint: Ghrelin Grows Hunger ; Leptin Lowers Hunger
Obesity
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)
type II diabetes (non-insulin dependent)
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
starvation
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)
anorexia nervosa
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
a deficient intake of proteins
kwashiorkor
a disorder that causes oedema, irritability, anorexia, ulcerating skin, and an enlarged liver.
omega-3 fatty acids functions in body
controlling blood clotting and building cell membranes in the brain
conditionally essential amino acids
Tyrosine can be synthesised by the human body when phenylalanine is present in the diet.
Arginine cannot be synthesised by infants so it must be present in the diet as well.
iron
needed for the functioning of haemoglobin. Iron atoms are the central atom in the non-protein, heme group of haemoglobin.
arsenic
necessary ultra-trace element for humans
iodine
synthesis of thyroid hormones, which can increase basal metabolic rate, affect protein synthesis, and help regulate long bone growth (in combination with growth hormone) and maturation of neurones
Sodium and potassium
propagation of the nerve impulse.
Calcium
muscle contraction
anaemia
(vitamin B12 deficiency),
beriberi
vitamin B1 deficiency
pellagra
vitamin B3 deficiency
scurvy
vitamin C deficiency)
