Introduction to Nutrition Flashcards
What 3 things will a healthy diet supply?
- energy
- building blocks for metabolism
- essential nutrients
what types of diets can lead to disease?
diets which fail to meet or significantly exceed an individual’s needs
What type of pattern is shown by dietary intake?
What does the graph look like?
a normal distribution
x axis - nutrient requirements
y axis - number of people
What is the EAR and where would it be found on the dietary intake graph?
estimated average requirement
it is in the centre of the normal distribution graph
What is described by the EAR?
Half of the population usually needs more than the EAR, and half needs less
The EAR is sufficient for 50% of the population
What is the LRNI and where would it be found on the dietary intake graph?
Lower reference nutrient intake
This is 2 standard deviations below the EAR (mean)
What is described by the LRNI?
LRNI is sufficient for 2.5% of the population, who have low needs
It does not meet the needs of 97.5% of the population
what is the RNI and where is it found on the dietary intake graph?
Reference nutrient intake
It is 2 standard deviations above the EAR (mean)
What is described by the RNI?
This is sufficient for around 97.5% of the population
The risk of deficiency is very small if the average intake of the population is the RNI
What is meant by the ‘safe intake’?
This is the safe upper limit for vitamins and minerals where an excess may be harmful
Why is safe intake used?
It is a range for which there is not enough information to estimate RNI, LRNI and EAR
Why is energy balance important?
it is the key to maintenance of a healthy weight
What is the “equation” for energy balance in someone of a healthy weight?
energy intake = energy expenditure
What does energy intake depend on?
Energy intake varies depending on age and gender
Why do people tend to gain weight as they get older?
In young adults, there is little change in requirements for energy intake
As you get older, requirements begin to decline
If you carry on eating as much as you used to, you will begin to gain weight with age
what does energy expenditure depend on?
Basic metabolic rate and the amount/intensity of physical activity
basic metabolic rate depends on age, weight and sex
What are macronutrients?
Macronutrients include fats, carbohydrates and proteins
They can be used immediately for energy generation
How are excess fats and carbohydrates stored?
Excess fats are stored as triacylglycerols in the adipose tissue
Excess carbohydrates are stored as glycogen
What is the main source of energy?
Fat stores provide 80-90% of total energy
Why is there no storage of protein?
what happens if there is a need for protein?
Amino acids cannot be stored
In starvation, muscle tissue can be metabolised for energy or to provide amino acids for other reactions
How much protein is required by an average adult daily?
an average adult requires 0.75g protein per kg of body weight
A typical 75kg man needs 50g protein daily
How much protein would be required by an athlete/bodybuilder daily?
1.2-1.7 g per kg of body weight
why are proteins not stable?
They are constantly being synthesised and degraded
If a muscle is not used, it is rapidly degraded
How do proteins vary in their rate of turnover?
Enzymes have a rapid turnover and a half-life in terms of seconds
Structural proteins (e.g. collagen) have a half-life in terms of tens of days
what is the equation for nitrogen balance in a healthy individual?
nitrogen intake = nitrogen excretion
When does negative nitrogen balance occur?
when nitrogen intake is less than nitrogen excretion
This occurs during fasting and illness
what happens if insufficient amino acids are taken in through the diet?
the body begins to break down proteins for energy
it secretes more ammonia in the urine (in the form of urea) than is being taken in
When does positive nitrogen balance occur?
When nitrogen intake exceeds nitrogen excretion
This happens during growth, pregnancy and after major surgery as the body is building new tissue
How many essential amino acids are there?
What is meant by an essential amino acid?
There are 9 essential amino acids
These cannot be synthesised by humans and must be obtained from the diet
what are the 9 essential amino acids and how can they be remembered?
Methionine Valine Histidine Leucine Phenylalanine Tryptophan Isoleucine Lysine Threonine
(Many Very Happy Little Pigs Take Iced Lemon Tea)
What is an example of an amino acid which is only required in the diet under certain conditions?
Arginine
it can be synthesised by the body, but during pregnancy the body struggles to synthesise enough
what is the difference in the kcal provided by fat and carbohydrate/protein?
How does this relate to the need for triacylglycerols?
Triacylglycerols are needed for energy
1g of fat provides 9 kcal
1g of carbohydrate/protein provides 4 kcal
What is the difference in the way in which carbohydrates and lipids are stored?
The body can store an unlimited amount of triacylglycerols in adipose tissue
The amount of glycogen that can be stored is limited
what type of molecules are cholesterol and fatty acids important precursors for?
Hormones and prostaglandins
Prostaglandins are involved in inflammation and smooth muscle contraction
Cholesterol is a precursor for vitamin D and steroid hormones
Other than triacylglycerol storage, what are the functions of adipose tissue?
- protection of vital organs
2. giving shape to the face and body
what are the typical properties of saturated fatty acids?
- they have no double bonds
- they are solid at room temperature
- they are typically found in meat and dairy products
What are the properties of monounsaturated fats?
- they have one double bond
- they are fluid at room temperature
- they are found in olive and peanut oil
What are the typical properties of polyunsaturated fats?
- they contain more than one double bond
- they are fluid at room temperature
- they are found in corn and sunflower oil
What are the typical properties of trans (hydrogenated) fats?
- they contain trans double bonds, opposed to cis double bonds
- they are found in cakes, biscuits and pastry
What is the consequence of trans fats having a trans double bond?
It makes them more solid
This increases the risk of heart disease
What is the recommended % of dietary intake that should come from different types of fat?
saturated fats - 11%
monounsaturates (cis) - 12%
polyunsaturates (cis) - 6%
trans-fats - <2%
total fat - <35% (30% is desirable)
What is the typical fat consumption of an average person?
They tend to consume low levels of trans-fats (0.7%) but a higher than ideal amount of saturated fat (12.5%)
What are the 2 classes of essential fatty acids?
What are they needed for?
Omega 6 and Omega 3
They are needed for the synthesis of hormones
How are the bonds in Omega 3 and 6 counted?
From the opposite end of the molecule to the carboxyl group
why is it advised that 2 portions of oily fish should be eaten each week?
they are a good source of omega 3 polyunsaturated fatty acids
this helps to decrease the risk of heart disease
What are the 4 categories of carbohydrates?
- polysaccharides
- disaccharides
- monosaccharides
- non-starch polysaccharides
what are polysaccharides?
most of our intake comes from polysaccharides
this is mainly starch from plant tissue but also glycogen from animal tissue
What is our main source of disaccharides?
sucrose (sugar)
what are the main monosaccharides in the diet?
glucose and fructose
these are the constituents of sucrose
What is meant by a non-starch polysaccharide?
Why are they needed?
This is dietary fibre
It prevents constipation
What are the recommended intakes for carbohydrates?
Free sugar - < 5%
Intrinsic and milk sugars, and starch - 39%
Total carbohydrate - 50%
Dietary fibre - 18 g per day
What are intrinsic sugars?
naturally occurring sugars
What is a typical average adult’s consumption of free sugar like?
There has been a slow decline in free sugar consumption
It is still around twice the recommended value
What are the risk factors associated with a high intake of free sugar?
- diets high in sugar are high in calories - increases risk of obesity
- high levels of fructose are linked to insulin resistance, metabolic syndrome and type 2 diabetes
What are the most common sources of free sugar?
- sugar/preserves
- sweetened soft drinks
- biscuits, cakes, buns, pastry, etc.
- alcoholic drinks
- fruit juice
- sweetened milk products
- chocolate and confectionary
What are micronutrients?
Vitamins and minerals
What are vitamins?
Organic compounds required for normal metabolic function, which cannot be synthesised by the body
How are vitamin deficiencies treated?
By giving the deficient vitamin to restore appropriate levels
What are the 2 types of vitamin?
How much is needed daily?
Fat-soluble and water-soluble
They are required in small amounts - micrograms/milligrams
How can you remember which vitamins are water and fat soluble?
All B vitamins and vitamin C are water-soluble
what are the water-soluble vitamins?
- B1 (thiamin)
- B2 (riboflavin)
- B3 (niacin)
- B5 (pantothenic acid)
- biotin (B7)
- B6 (pyridoxal phosphate)
- B9 (folic acid)
- B12 (cobalamin)
- Vitamin C (ascorbic acid)
What are the fat-soluble vitamins>
E, K, A, D
What are the majority of vitamines converted into?
Molecules that act as coenzymes
Except for A, D, E
How do Vitamins A, D and E work?
They enter the nucleus and alter the level of transcription
This alters the amount of proteins which are produced
What is thiamin (B1) needed for and what is the effect of a deficiency?
it is a cofactor in decarboxylation reactions which release CO2
deficiency leads to Beri-Beri
this is muscle weakness, nerve damage, can affect heart
What is riboflavin (B2) needed for and what is the effect of a deficiency?
it is a constituent of cofactors (e.f. flavin adenine dinucleotide, FAD)
it is involved in many aspects of the metabolism of fats, carbohydrates and proteins
deficiencies are very rare as the cofactors bind very tightly to the enzymes
What is niacin (B3) needed for and what is the effect of a deficiency?
It is a constituent of cofactors e.g. NADH
Deficiency leads to pellagra
diarrhoea, depression, dermatitis, death
What is pantothenic acid (B5) needed for and what is the effect of a deficiency?
it is a constituent of coenzyme A - which is needed in energy and fat metabolism
deficiency is unknown as it is found in almost all foods
What is biotin (B7) needed for and what is the effect of a deficiency?
it is a prosthetic group that acts as a carrier for CO2 in carboxylation reactions
deficiencies are very rare
What is pyridoxal phosphate (B9) needed for and what is the effect of a deficiency?
cofactor in enzymes involved in protein metabolism, haem synthesis, neurotransmitter synthesis, modulation of steroid hormone action
deficiency leads to depression, confusion, inflammation of tongue or mouth
What is folic acid (B9) needed for and what is the effect of a deficiency?
1-C transfers, particularly in DNA synthesis
Deficiency leads to neural tube defects
e.g. spina bifida, anencephaly, macrocytic anaemia
What is cobalamin (B12) needed for and what is the effect of a deficiency?
methionine synthesis and fatty acid metabolism
deficiency leads to macrocytic anaemia and irreversible neurological damage
What is vitamin C needed for and what is the effect of a deficiency?
collagen synthesis and role as an antioxidant
deficiency leads to scurvy where symptoms are caused by weakened collagen
What is vitamin A needed for and what is the effect of a deficiency?
vision (rod cell function) and as a transcriptional regulator
deficiency causes blindness and an excess can cause birth defects
What is vitamin D needed for and what is the effect of a deficiency?
bone formation and maintenance, immune regulation, cell differentiation, muscle function
deficiency leads to rickets in children and osteomalacia in adults
What is Vitamin E needed for and what is the effect of a deficiency?
it is an anti-oxidant which prevents lipid oxidation in membranes
deficiency causes neurological problems and is found in those who have difficulty absorbing fats
What is Vitamin K needed for and what is the effect of a deficiency?
cofactor for enzymes that activate blood clotting proteins, involved in bone maintenance
deficiency in newborns causes bleeding, rare in adults
