D1 Human Nutrition Flashcards
What is a nutrient?
A nutrient is a chemical substance found in foods that is used in the human body
What are the 6 classes of nutrient?
There are six classes of nutrients – carbohydrates, proteins, lipids, vitamins, minerals and water
What are essential nutrients?
Essential nutrients are those that cannot be synthesised by the body and must be ingested as part of the diet
What are non-essential nutrients?
Non-essential nutrients can be made by the body or have a replacement nutrient which serves the same dietary purpose
Are carbohydrates essential nutrients?
NO
Carbohydrates are not considered essential nutrients as human diets can obtain energy from other sources without ill effect
What is malnutrition?
Malnutrition is a health condition caused by a deficiency, imbalance or excess of nutrients in the diet
What can cause malnutrition? 2
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
Are symptoms of malnutrition the same for each imbalance?
NO
The symptoms of malnutrition will vary according to the specific nutrient and the type of imbalance involved
What are common signs of malnutrition?
Common signs of malnutrition included stunted growth and wasting (undernutrition), as well as obesity (over nutrition)
How can the energy content of food be estimated? (experimentally)
The energy content of food can be estimated by burning a sample of known mass and measuring the energy released via calorimetry
What does combustion of food release?
Combustion of the food source causes the stored energy to be released as heat, which raises the temperature of water
What is the equation used to calculate the energy content of food via calorimetry?
Energy (joules) = Mass of water (g) × 4.2 (J/gºC) × Temperature increase (ºC)
WHat is the biggest source of error in calorimetry?
The biggest source of error in calorimetry is usually caused by the unwanted loss of heat to the surrounding environment
What should be kept constant in calorimetry?
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)
Which nutrient is most commonly used an energy source and why?
Carbohydrates are preferentially used as an energy source because they are easier to digest and transport
What type of energy are lipids used for and why?
Lipids can store more energy per gram but are harder to digest and transport (hence are used for long-term storage)
What happens when proteins are used for energy?
Protein metabolism produces nitrogenous waste products which must be removed from cells
What are amino acids?
Amino acids are the monomeric building blocks from which proteins are constructed
How many amino acids are there?
here are 20 different amino acids which are universal to all living organisms
What categories do amino acids fit into?
Amino acids can be either essential, non-essential or conditionally non-essential according to dietary requirements
WHat are essential amino acids?
Essential amino acids cannot be produced by the body and must be present in the diet
What are non-essential amino acids?
Non-essential amino acids can be produced by the body and are therefore not required as part of the diet
What are conditionally non-essential amino acids?
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
What happens if there is a shortage of one or more of the essential amino acids?
A shortage of one or more essential amino acids in the diet will prevent the production of specific proteins
What is a lack of amino acids called?
This is known as protein deficiency malnutrition and the health effects will vary depending on the amino acid shortage
What is PKU?
Phenylketonuria (PKU) is a genetic condition that results in the impaired metabolism of the amino acid phenylalanine
What does PKU affect regarding genetics?
It is an autosomal recessive disease caused by a mutation to the gene encoding the enzyme phenylalanine hydroxylase
What is the typical role of PAH?
Phenylalanine hydroxylase (PAH) normally converts excess phenylalanine within the body into tyrosine
What happens as a result of the lack of PAH?
In people with PKU, the excess phenylalanine is instead converted into phenylpyruvate (also known as phenylketone)
What happens when phenylalanine is constantly being converted into phenylketone?
This results in a toxic build up of phenylketone in the blood and urine (hence phenylketonuria)
What can untreated PKU lead to?
Untreated PKU can lead to brain damage and mental retardation, as well as other serious medical problems
How are infants with PKU at birth?
Infants with PKU are normal at birth because the mother is able to break down phenylalanine during pregnancy
How is PKU diagnosed?
Diagnosis of PKU is made by a simple blood test for elevated phenylalanine levels shortly after birth
How is PKU treated?
PKU is treated by enforcing a strict diet that restricts the intake of phenylalanine to prevent its build up within the body
What does a PKU diet contain?
This low-protein diet should include certain types of fruits, grains, vegetables and special formula milk
What should a PKU diet be supplemented with?
This diet should be supplemented with a medical formula that contains precise quantities of essential amino acids
Is a person able to live normally with PKU?
Patients who are diagnosed early and maintain this strict diet can have a normal life span without damaging symptoms
Why are most fatty acids non-essential? What are the exceptions (general)?
Humans can synthesise most fatty acids from carbohydrates, but two (cis)-polyunsaturated fatty acids are considered essential
What are the 2 essential fatty acids?
Alpha-linolenic acid (an omega-3 fatty acid) and linoleic acid (an omega-6 fatty acid) cannot be synthesised by the body
WHy are these 2 fatty acids essential?
this is because humans lack the enzyme required to introduce double bonds at the required position of the carbon chain
What are essential fatty acids used for?
Essential fatty acids are modified by the body to make important lipid-based compounds (such as signalling molecules)
What is linked to a deficiency of essential fatty acids?
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
What are foods rich in essential fatty acids?
Foods rich in essential fatty acids (omega-3 and omega-6) include fish, leafy vegetables and walnuts
How are fats and cholesterol transported?
Fats and cholesterol cannot dissolve in the bloodstream and so are packaged with proteins (to form lipoproteins) for transport
What are LDLs?
Low density lipoproteins (LDLs) carry cholesterol from the liver to the body (hence raise blood cholesterol levels)
What are HDLs?
High density lipoproteins (HDLs) carry excess cholesterol back to the liver for disposal (hence lower blood cholesterol levels)
What does the mix of fatty acids consumed affect?
The mix of fatty acids consumed as part of a diet directly influences the levels of cholesterol in the bloodstream:
How do saturated fatty acids affect the levels of cholesterol in the bloodstream?
Saturated fats increase LDL levels within the body, raising blood cholesterol levels
How do trans fats affect the levels of cholesterol in the bloodstream?
Trans fats increase LDL levels and lower HDL levels, significantly raising blood cholesterol levels
How do Cis-polyunsaturated fats affect the levels of cholesterol in the bloodstream?
Cis-polyunsaturated fats raise HDL levels, lowering blood cholesterol levels
What do high cholesterol levels in the bloodstream lead to?
High cholesterol levels in the bloodstream lead to the hardening and narrowing of arteries (atherosclerosis)
What happens when there are high LDL levels in the bloodstream?
When there are high levels of LDL in the bloodstream, the LDL particles will form deposits in the walls of the arteries
What does the accumulation of fat in arterial walls lead to?
The accumulation of fat within the arterial wall leads to the development of plaques which restrict blood flow
What happens if coronary arteries become blocked?
If coronary arteries become blocked, coronary heart disease (CHD) will result – this includes heart attacks and strokes
What are vitamins?
Vitamins are organic molecules with complex chemical structures that are quite diverse and hence categorised by groups
Is there a limit to the consumption of water soluble vitamins?
Water soluble vitamins need to be constantly consumed as any excess is lost in urine (e.g. vitamins B, C)
Where can fat soluble vitamins be stored?
Fat soluble vitamins can be stored within the body (e.g. vitamins A, D, E, K)
What are many functions of vitamins? (3)
The functions of vitamins are as diverse as their structure, although many function as cofactors, antioxidants or hormones
Are many vitamins non/essential?
Many vitamins are essential as they cannot be synthesised by the body and their absence may cause a deficiency disease
What is ascorbic acid and its use?
Ascorbic acid is a form of vitamin C that is required for a range of metabolic activities in all animals and plants
What is the role of ascorbic acid in mammals? (4)
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
Can humans produce ascorbic acid?
NO
Ascorbic acid is made internally by most mammals from monosaccharides – but it is not produced by humans
How do most humans consume ascorbic acid?
Consequently, human must ingest vitamin C as part of their dietary requirements in order to avoid adverse health effects
What does a vitamin C deficiency lead to?
A deficiency in vitamin C levels will lead to the development of scurvy and a general weakening of normal immune function
What are common sources of vitamin C?
Common food sources of vitamin C include citrus fruits and orange juice
What is the role of vitamin D?
Vitamin D is involved in the absorption of calcium and phosphorus by the body – which contribute to bone mineralisation
What happens to elements associated with vit D if there is a deficiency?
In the absence of sufficient amounts of this vitamin, these elements are not absorbed but instead excreted in the faeces
What does a vit D deficiency lead to?
This can lead to the onset of diseases such as osteomalacia (where bones soften) or rickets (where bones are deformed)
Can vit D be synthesised?
yes
Vitamin D can be naturally synthesised by the body when a chemical precursor is exposed to UV light (i.e. sunlight)
Where can vit D be stored?
The vitamin D may be stored by the liver for when levels are low (e.g. during winter when sun exposure is reduced)
What may affect vit D synthesis?
Individuals with darker skin pigmentation produce vitamin D more slowly and hence require greater sun exposure
Who are vit D deficiencies usually restricted to?
Vitamin D deficiencies are usually restricted to individuals with highly limited sun exposure (e.g. elderly, certain ethnicities)
What is the problem with sun exposure?
While excess sun exposure is beneficial for vitamin D production, it also increases the risks of developing skin cancers
What are dietary minerals?
Dietary minerals are chemical elements required as essential nutrients by organisms
What minerals are considered non-essential?
Minerals present in common organic molecules are not considered essential – e.g. C, H, O, N, S
What are examples of minerals?
Minerals include calcium (Ca), magnesium (Mg), iron (Fe), phosphorus (P), sodium (Na), potassium (K) and chlorine (Cl)
What is the use of Ca, P, Mg?
Major constituents of structures such as teeth and bones (e.g. Ca, P, Mg)
What is the use of Na, K, Cl?
Important components of body fluids (e.g. Na, K, Cl)
What is the use of Na, K, Cl?
Important components of body fluids (e.g. Na, K, Cl)
What is the use of Fe, P, I?
Cofactors for specific enzymes or components of proteins and hormones (e.g. Fe, P, I)
What will happen if there is a deficiency in one or more minerals?
A deficiency in one or more dietary mineral can result in a disorder (e.g. lack of calcium can affect bone mineralisation)
Apart from animals, what organism requires minerals?
Minerals are also important in plant development, making fruits and vegetables a good source of certain dietary minerals
What is the role of magnesium in plants?
Magnesium is an important component of chlorophyll (required for photosynthesis)
What is the role of potassium in plants?
Potassium is an inorganic salt found within the sap of a plant (maintains water potential)
What is the role of calcium in plants?
Calcium is important for plant root and shoot elongation
What controls appetite?
Appetite is controlled by hormones produced in the pancreas, stomach, intestines and adipose tissue
Where are the hormones secreted by organs involved in appetite control sent?
These hormones send messages to the appetite control centre of the brain (within the hypothalamus)
What will hormonal signals trigger?
Hormonal signals will either trigger a feeling of hunger (promote feasting) or satiety (promote fasting)
What 3 organs can release hormones involved in appetite?
stomach
adipose tissue
pancread
How does the stomach release appetite hormones?
Stretch receptors in the stomach and intestine become activated when ingested food distends these organs
How does the adipose tissue release appetite hormones?
Adipose tissue releases hormones in response to fat storage
How does the pancreas release appetite hormones?
The pancreas will release hormones in response to changes in blood sugar concentrations
What can hormones (related to appetite) do? (basic)
Hormones will either stimulate or inhibit the appetite control centre to promote sensations of hunger or satiety
What hormones trigger a hunger response?
Hormones that trigger a hunger response include ghrelin (from stomach) and glucagon (from pancreas)
Ghrelin Grows Hunger
What hormones trigger a satiety response>?
Hormones that trigger a satiety response include leptin (from adipose tissue) and CCK (from intestine)
Leptin Lowers Hunger
What can change in diet/ appetite control result in?
Changes in diet and appetite control may result in individuals over-indulging or under-indulging during meals
What will happen in individuals who overeat?
Individuals who overeat are likely to gain weight and develop obesity-related illnesses
What will happen in individuals who undereat?
Individuals who undereat are likely to lose weight and exhibit starvation symptoms
What is clinical obesity?
Clinical obesity (BMI > 30) describes a significant excess in body fat
What 2 factors cause obesity?
Increased energy intake
Decreased energy expenditure
How does increased energy intake contribute to obesity?
overeating or an increased reliance on diets rich in fats and sugars
How does decreased energy expenditure contribute to obesity?
less exercise resulting from an increasingly sedentary lifestyle
What are individuals who suffer from obesity more prone to?
Individuals who are overweight or obese are more likely to suffer from hypertension (abnormally high blood pressure)
How does excess weight contribute to hypertension?
Excess weight places more strain on the heart to pump blood, leading to a faster heart rate and higher blood pressure
How does high cholesterol lead to hypertension?
High cholesterol diets will lead to atherosclerosis, narrowing the blood vessels which contributes to raised blood pressure
What is hypertension a precursor to ?
Hypertension is a common precursor to the development of coronary heart disease (CHD)
What other illness are overweight/obese people likely to suffer from?
Individuals who are overweight or obese are also more likely to suffer from type II diabetes (non-insulin-dependent)
When does Type II diabetes occur?
Type II diabetes occurs when fat, liver and muscle cells become unresponsive to insulin (insulin insensitivity)
What type of diet causes type II diabetes?
This typically results from a diet rich in sugars causing the progressive overstimulation of these cells by insulin
Generally, who is more likely to develop type II diabetes?
Hence overweight individuals who have a high sugar intake are more likely to develop type II diabetes
What is starvation?
Starvation describes the severe restriction of daily energy intake, leading to a significant loss of weight
What happens to the body due to starvation?
As the body is not receiving a sufficient energy supply from the diet, body tissue is broken down as an energy source
What is the effect of prolonged and severe starvation?
This leads to muscle loss (as muscle proteins are metabolised for food) and eventually organ damage (and death)
What is anorexia nervosa?
Anorexia nervosa is an eating disorder in which individuals severely limit the amount of food they intake
In whom is anorexia nervosa most common?
It is most common in young females with body image anxiety and can potentially be fatal if left untreated
What is the most common cause o death due to anorexia?
In severe anorexia, the body begins to break down heart muscle, making heart disease the most common cause of death
How does anorexia lead to heart disease?
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
What is the RDI?
The recommended daily intake for a nutrient (RDI) is the daily dietary level required to meet the requirements of health
What causes the RDI to vary?
It is an estimate only and will vary according to age, gender, activity levels and medical conditions
What are the recommendations of the RDI based off of?
The recommendations are based on a daily energy intake of 8400 kJ (2000 kcal) for healthy adults
How is the RDI found on food packages?
On food packages, this information is usually presented as a percentage of a daily total (based on identified serving size)
How can weight change be monitored?
Dietary intake can be recorded and compared against levels of energy expenditure in order to monitor weight change
