A.1.1 Define nutrient.
A nutrient is a chemical substance found in foods that is used in the body.
A.1.2 List the types of nutrient that are essential in the human diet
Link to Chemistry of Life 3.1 and 3.2
Sources: (1) (2) (3) (4)
A.1.3 State that non-essential amino acids can be synthesized in the body from other nutrient
Biosynthesis is the production of non-essential nutrients in the body from components of essential nutrients.
If these nutrients are present in the diet, the body does not need to expend the energy on biosynthesis.
Sources: (4) (3) (2)
A.1.4 Outline the consequences of protein deficiency malnutrition
If the intake of protein is too low, it could lead to a protein deficiency malnutrition - a lack of essential amino acids. These amino acids are required for production of proteins, such as plasma proteins, extracellular proteins, DNA and plasma membranes in the body.
Protein deficiency malnutrition is a key factor in kwashiorkor. Symptoms include:
Muscle and skin problems
Impaired mental development
Immune system impairment
Edema (swelling in the abdomen and legs as plasma proteins responsible for balancing tissue fluids are not produced, so fluid builds up)
Sources: (5) (6)
A.1.5 Explain the causes and consequences of phenylketonuria (PKU) and how early diagnosis and a special diet can reduce the consequences
Link to 3.5, 3.6 and 4.1
1. PKU is the result of a mis-sense mutation in the PAH gene.
2. It is autosomal and recessive.
The PAH gene codes for the enzyme tyrosine hydroxylase .
The essential amino acid phenylalanine cannot be converted to tyrosine, so builds up to dangerous levels.
This disorder is progressive : its effects build up over time and lead to ongoing deterioration. Symptoms:
a blood test at birth will detect the presence of absence of the enzyme. As this is a cumulative disorder, the earlier it is diagnosed and the diet is started, the less chance there is of severe complications.
A phenylalanine-controlled diet from birth is essential. Foods containing phenylalanine are minimised, including dairy, aspartame sweeteners, breastmilk, nuts and meat. Tyrosine supplementation may be used.
Sources: (7) (8)
A.1.6 Outline the variation in the molecular structure of fatty acids, cis- and trans- unsaturated fatty acids, monounsaturated and polyunsaturated fatty acids.
Link to 3.2.2
Fatty acids have the same general structure, but there is variation in the bonds between carbon atoms.Saturated fats have no double bonds: all possible valences have been occupied. A mono-unsaturated fatty acid has C=C double bond, whereas as polyunsaturated fatty acid has two or more C=C double bonds.
There is also variation in the structure of unsaturated fatty acids. cis- isomers have the hydrogen atoms on the same side of the C=C double bond, whereas trans- isomers have the hydrogen atoms on opposite sides. Most trans- fats are created artificially.
In unsaturated fatty acids, the omega-number indicates the position of the first double bond, from the CH3 group. An omega-3 fatty acid has the C=C double bond at the third bond along the chain.
(i) Hydrogenation is a process which is used to create trans- fatty acids from cis- fatty acids.
(ii) Hydrogen is used to saturate some of the double bonds in an oil, making solid fats from liquid oils: making margarine from vegetable oil.
(iii) Although this has benefits with regard to storage and mass-production, it has health effects.
(iv) Oleic acid (CH3(CH2)7CH=CH(CH2)7COOH) is an omega-9 fatty acid. It is a component of olive oil in its cis- form. Its isomer, elaidic acid (trans-oleic acid) is found in hydrogenated vegetable oil.
Sources: (9) (3) (4)
A.1.7 Evaluate the health consequences of diets rich in the various types of fatty acid
Dietary studies are difficult to control sufficiently to gain really reliable data. Where data are produced it may not be possible to conclude causal relationships from correlation. Care must be taken to think critically about nutrition-based news stories and articles.
Sources: (10) (9) (4) (8)
A.1.8 Distinguish between vitamins and minerals in terms of their chemical structure
Link to 3.2.1 and 3.2.2
Vitamins are organic compounds made by plants or animals, whereas minerals are inorganic ions. Minerals can be found in water, soil and many organic food types as a result of uptake.
Sources: (11) (4) (12)
A.1.9 Outline two of the methods that have been used to determine the recommended daily intake of vitamin C
Vitamin C (ascorbic acid) is essential in the human diet. It maintains mucus membranes as a component of collagen, and promoted healing and skin growth. Deficiency of vitamin C can lead to scurvy, characterized by bleeding hair follicles, gums and liver spots on the skin. In extreme cases it can be fatal.
Recommended Daily Intakes (RDI) of vitamin C have been set at 45-60mg day-1. These levels were determined based on a number of experiments into levels of vitamin C that gave optimum benefit.
Humans and guinea pigs cannot synthesise vitamin C, so it is possible to measure the effects of varying vitamin C doses in carefully controlled experiments.
Human trials: observe the symptomatic effects of varying doses of vitamin C supplementation
Conscientious objectors from WWII volunteered to take part in a series of medical trials in Sheffield over a four-year period.
In one of these, 20 volunteers were used to measure the effects of varying vitamin C concentrations.
Weeks 1-6: No vitamin C in foods, but all given 70mg supplement
Weeks 7-end (8 months): 3 kept on 70mg per day, 7 were given 10mg per day and 10 were given no vitamin C at all.
Measurement: periodic incisions were made on volunteer’s thighs, and healing time and strength of healed tissue were observed. Blood and urine vitamin C concentrations were recorded.
Outcomes: no ill effects were recorded in the 70mg or 10mg groups. The 0mg group developed scurvy within 6-8 months and some serious side effects were recorded, including one who experienced heart problems, which were rectified after he was given vitamin C.
Another example of a human trial took place in a prison in Iowa, and the outcome was similar, with a recommended intake of around 30mg day-1.
Guinea pig trials: observe the effect of vitamin C concentration on collagen structure
After periods of varying vitamin C supplementation and measurement of blood and urine vitamin C levels, guinea pigs were sacrificed and the structure of collagen fibres observed. Guinea pigs with restricted vitamin C showed weaker collagen.
Sources: (13) (8) (4) (12)
A.1.10 Discuss the amount of vitamin C that an adult should consume per day, including the level needed to prevent scurvy, claims that higher intakes protect against upper respiratory tract infections, and danger of rebound malnutrition.
Recommended Daily Intakes (RDI) of vitamin C have been set at 45-60mg day-1.These are based on controlled experiments using human and animal subjects.
There is some debate on whether the RDI should be higher, with experts such as:
The evidence for the efficacy of these recommendations is not strong, yet some have suggested it can boost the immune system, prevent upper respiratory tract infections, decrease susceptibility to cancer and speed healing and recovery from illness. Large-scale, randomized and controlled trials of these claims have not taken place.
Some adverse effects of high dose vitamin C regimes can include instestinal problems and acidosis, but there is little data to suggest long-term harm. It has also been suggested that rebound malnutrition can occur as a result of systemic conditioning during long periods of high-dose supplementation: the body is accustomed to excreting large amounts of vitamin C and this continues once supplementation stops, leading to deficiency. The evidence for these claims is also weak.
Sources: (11) (14) (4) (12) (15) (16)
A.1.11 List the sources of vitamin D in human diets.
Vitamin D can be produced by skin as a response to sunlight.
It also can be found (in a slightly different form) in foods: fatty fish, fish oils, liver, eggs and some mushrooms.
In some countries, milk is supplemented with vitamin D.
A.1.12 Discuss how the risk of vitamin D deficiency from insufficient exposure to sunlight can be balanced against the risk of contracting malignant
Vitamin D is required to allow uptake of calcium, which is then used to produce bone matrix. Rickets, vitamin D deficiency, results from low levels of vitamin D, calcium or both. Symptoms of vitamin D deficiency include bow legs and stunted growth.
There is a strong negative correlation between increasing darkness of skin colour and vitamin D synthesis. Historically, darker-skinned populations were exposed to stronger sunlight for longer periods of time. Darker skin produces vitamin D more slowly, but offers protection against skin cancer (malignant melanoma).
Pale skinned people are more able to produce vitamin D, yet more susceptible to skin cancer.
Risks of vitamin D deficiency can be negated with supplementation or attention to dietary sources, whereas the risk of skin cancer can be reduced by covering pale skin, staying indoors or using sunblocks.
Sources: (17) (11) (4)
A.1.13 Explain the benefits of artificial dietary supplementation as a means of preventing malnutrition, using iodine as an example.
Link to 6.5.10,
Artificial supplementation can be used to ensure that a population has adequate access to essential nutrients, even if the supply of naturally-containing foods is limited. Some examples include adding fluoride to drinking water to prevent tooth decay, vitamin D supplementation of milk to prevent rickets or iodine supplementation of salt to prevent thyroid problems (hypothyroidism).
Iodine is essential in production of thyroxine, a hormone responsible for regulating metabolic rate in the body and therefore body temperature. Patients suffering from hypothyroidism are at risk of mental retardation and goiter, an extreme swelling of the thyroid glands in the neck. It can cause birth defects and miscarriages.
Worldwide supplementation of edible salt with iodine has greatly reduced incidence of iodine deficiency disorders, at very low cost and with minimal objection.
Genetic engineering is also being used to produce enhanced crops, such as beta-carotene rich golden rice, though there is more ethical debate concerning these methods.
Sources: (18) (19) (17) (1) (8)
A.1.14 Outline the importance of fibre as a component of a balanced diet
Links to 3.2, 3.8.6 and 6.1
Dietary fibre includes the components of foods which cannot be digested by the human body. This is largely cellulose, a structural component of the plant cell wall. Although it cannot be digested an absorbed into the blood, dietary fibre plays an important role in human health.
Provides bulk in food, allowing one to feel full when eating
Helps regulate blood sugar
Reduces blood cholesterol
Strengthens action of peristalisis in the intestine
Dietary fibre is sourced from vegetables, nuts, wholegrains and some fruits.
Source: (20) (8) (11)