Option A: Human Nutrition and Health Summary Notes

A1: Components of the Human DietA.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 dietEssential nutrients

(cannot be synthsesised in the body from other nutrients, so must be included in the diet)Non-Essential Nutrients

(Can be synthesized in the body or found from alternative sources. Dietary intake of these nutrients reduces the need for biosynthesis)

Water Some fatty acids (including omega-3 linolenic acid and omega-6 linoleic acid)

Some Vitamins (including A, some B vitamins, C, D, folate)

Dietary minerals (including iron, potassium, sodium, calcium, phosphorous and iodine) Some amino acids (including phenylalanine and methionine)

Carbohydrates (energy can come from other sources, such as lipids and proteins) Other lipids and fatty acids Other vitamins

Other minerals

Other amino acids

A.1.3 State that non-essential amino acids can be synthesized in the body from other nutrients

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 intake of protein is too low, it could lead to 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: Stunted growth

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)

A.1.5 Explain the causes and consequences of phenylketonuria (PKU) and how early diagnosis and a special diet can reduce the consequences

PKU is the result of a mis-sense mutation in the PAH gene. 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 cumulative and degenerative: its effects build up over time and lead to ongoing deterioration. Symptoms: skin disorders and intellectual disability. Heart problems and microcephaly can also develop in severe cases.

Diagnosis: 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.

Treatment: 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.

A.1.6 Outline the variation in the molecular structure of fatty acids, cis- and trans- unsaturated fatty acids, monounsaturated and polyunsaturated fatty acids. 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.

Hydrogenation is a process which is used to create trans- fatty acids from cis- fatty acids. Hydrogen is used to saturate some of the double bonds in an oil, making solid fats from liquid oils: making margarine from vegetable oil. Although this has benefits with regard to storage and mass-production, it has health effects.

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. A.1.6 Evaluate the health consequences of diets rich in the various types of fatty acid

Saturated FatsCis- fatty acidsTrans- fatty acids

Sources:

Animal fats butter, milk, cheese, red and white meat, eggs, palm oilSources:

Vegetable oils, such as olive oil, fish oilsSources:

Hydrogenated vegetable oils, margarine, some natural sources

All contribute to dietary intake and excess consumption is related to weight gain and coronary heart disease. Fat contains more energy per gram than carbohydrates or proteins.

-Can raise harmful LDL cholesterol

-Lead to atherosclerosis and coronorary heart disease-May promote beneficial HDL cholesterol and inhibit harmful LDL.

-omega 3 fatty acids linked to brain development-may have a greater negative effect on LDL cholesterol and increased risk of atherosclerosis and CHD than saturated fats-some natural trans- fats may have less harmful impacts

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. A.1.8 Distinguish between vitamins in minerals in terms of their chemical structure

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.

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 supplementationConscientious 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): Dose: 0 mg per day10mg per day70 mg per day

Measurements:-Blood and urine vitamin C.

-3cm incisions made on thighs, stitched. Observed healing time and strength of scar tissue. Repeated periodically

Effects: -Scurvy in all cases within 6-8 months.

-One patient experienced severe heart complications (rectified after being given vitamin C)No evidence of scurvy or other ill effects.

Outcome: recommendation set at 30mg day-1Another 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. 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 Nobel-winner Linus Pauling suggesting that megadoses (1000mg or more) are required per day. The Vitamin C Foundation recommend 3 doses of 1000mg per day.

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. 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 melanoma.

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.

A.1.13 Explain the benefits of artificial dietary supplementation as a means of preventing malnutrition, using iodine as an example.

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.

A.1.14 Outline the importance of fibre as a component of a balanced diet

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

Reduces constipation

Dietary fibre is sourced from vegetables, nuts, wholegrains and some fruits.

A2: Energy in Human Diets

A.2.1 Compare the energy content per 100g fat, carbohydrate and protein.

Various units of energy can be used on food labels, but we use the unit kJ (kilojoules).

Comparative energy contents (approximate), kJ per 100g:

Fats CarbohydratesProteins

400017601720

Notice that fats contain more than double the energy per unit mass than carbohydrates or proteins. Some food labels use Calories, which is the more common term in public science. One calorie is the energy required to raise the temperature of 1kg water by 1oC. One food Calorie is actually 1000 calories (1kcal). One food Calorie is equivalent to 4.18kJ. Question: what is the link between the energy content of fats and their metabolism in respiration? Refer to the role of CoA.

A.2.2 Compare the main dietary sources of energy in different ethnic groups.

Dietary energy can come from various sources, carbohydrates, proteins or fats, depending on the foods available to a population. These staples make up the bulk of a populations diet, and are generally crops.

Region/ groupMain food energy source

Continental Europeans, USAWheat (as bread or pasta)

UK & Northern EuropePotatoes, wheat (bread) or rye

Central Africa and BrazilCassava (sweet potato)

Americas and AfricaMaize (corn)

AsiaRice

Eskimo tribesWhale and fish meat

Isolated island populationsFish

A.2.3 Explain the possible health consequences of diets rich in carbohydrates, fats and proteins.

CarbohydratesProteinsFats

As all macronutrients contain energy, high intake can lead to storage of excess energy as fat, therefore weight gain, possible obesity and coronary heart disease. The ideal is a balance of all three to ensure sufficient intake of all essential nutrients.

-Carbohydrates are digested to monosaccharides (sugars) which are absorbed into the blood. Prolonged high intake can lead to diabetes as the liver become less sensitive to insulin.

-Carbohydrates which cannot be digested (such as cellulose) count as fibre, which has health benefits. -Sufficient protein intake is required to provide essential amino acids. -There is minimal risk in a diet high in protein, though some kidney problems may be reported.

-Some weight-loss diets promote replacing carbohydrates with proteins. These may result in long-term malnutrition as nutrient rich foods are avoided. - strong correlation between high fat intake and obesity, as well as coronary heart disease- saturated and trans- unsaturated fats pose a higher risk than cis- unsaturated fats

- some positive effects of diets rich in cis- fats, with regard to reducing harmful cholesterol

A.2.4 Outline the function of the appetite control centre of the brain.

Appetite is controlled in the hypothalamus of the brain. Control is both nervous and hormonal: some hormones trigger appetite-stimulating neurons, others trigger appetite-inhibiting neurons.

An empty stomach releases the hormone gherin, which triggers appetite-stimulating hormones, leading to hunger. When food enters the stomach, gherin production is stopped, reducing hunger.

Appetite is also inhibited when:

1. Food entering the intestine stimulates release of PYY3-36 hormone.

2. Carbohydrate and protein digestion stimulate release of insulin hormone from the pancreas.

3. Fat storage stimulates release of leptin hormone from the pancreas. This is enhanced by insulin. These three hormones trigger appetite-inhibiting neurons in the appetite control centre.

There are strong links to malfunction of any of these pathways and obesity, as the individual eats more than is required.

A.2.5 Calculate body mass index (BMI) from the body mass and height of a person.

e.g. 1: 70kg man, 1.8m tall. BMI = 70 / 1.82 = 21.6

A.2.6 Distinguish, using the body mass index, between being underweight, normal weight, overweight and obese.

BMIBelow 18.518.5-24.925.0-29.930.0 and above

CategoryUnderweightNormalOverweightObese

Limitations of the BMI using this table:

Race, gender and age are not considered

No distinction is made on body fat/water/muscle composition

Examples:

e.g.Height (m)Body Mass (kg)BMICategory

11.87021.6Overweight

21.97019.4Normal

31.912033.2Obese

A.2.7 Outline reasons for increasing rates of clinical obesity in some countries, including availability of cheap high-energy foods, large portion sizes, increasing use of vehicles for transport, and a change from active to sedentary occupations. Clinical obesity is an excess of body fat. Generally it is caused by consuming more energy than is used in activity, with the excess stored as body fat. Obesity carries a reduced life expectancy, high risks of CHD, diabetes, heart attacks and strokes. The obesity epidemic is on the increase globally, in developed nations in particular. There are many contributing factors:

Food availabilityPackaged, sugary or fatty foods are energy-dense they contain a lot of energy per unit mass. A large mass is consumed to feel full, but an excess of energy is also consumed.

Portion sizesA trend to supersizing meals and overeating contributes to intake of excess energy.

TransportationIncreasing use of vehicles as transport means less energy is burned off than if one walked or used pedal-power.

Sedentary lifestylesProfessions are increasingly information-based and office-centred, so workers are less active. Engagement in TV, video games and other passive hobbies reduces exercise in children and adults.

PovertyLinked to food availability. Often the cheapest option for the poor in developed nations is the packaged, processed, high-energy alternative. Whole foods and fresh ingredients tend to be more expensive.

Genetic factorsGenetic factors are strongly linked to addiction, compulsive eating, susceptibility to weight gain, heart disease or diabetes or to problems with appetite control mechanisms.

A.2.8 Outline the consequences of anorexia nervosa.

Anorexia nervosa is an eating disorder in which the patient severely limits food intake. It is a medical condition with mental and physiological causes. It is closely associated with body image and meeting aesthetic standards imposed by culture. It is most common in females, but does occur in males.

Health consequences include:

MalnutritionDeficiency in some or all essential nutrients as a result of not eating can lead to any of the effects below.

Hormone imbalancePeriods stop, problems in pregnancy, growth and development

Mental healthMood swings, poor concentration, phobias and paranoia

BloodAnemia and circulatory problems, including heart weakness

Muscle and boneLoss of muscle mass, lack of strength, osteoporosis, more easily injured

Immunity and healingSusceptible to infections, recovery and healing are impaired

Skin problemsDry, easily damaged, discoloration

DeathAs a result of prolonged, severe starvation

A3: Special Issues in Human Nutrition

A.3.1 Distinguish between the composition of human milk and artificial milk used for bottle-feeding babies.

BreastmilkFormula

ColostrumPresent in first feeds. Stimulates newborn digestion.Not present

Antibodies Present in colostrums in high doses, and subsequent milk. Not present

ProteinLower, but more easily digested and absorbed. Human. Higher, but harder to digest and absorb. Bovine sources.

CarbohydratesHigher in lactose, linked to brain development. Lower in lactose. May come from glucose.

Fatty acidsHuman fatty acids. Palm oil or alternatives .

Vitamins and mineralsMay be lower, but easier to absorb. Higher, but harder to absorb.

A.3.2 Discuss the benefits of breastfeeding.

BenefitEffect

ImmunityColostrum and early breastmilk contain high concentrations of antibodies, protecting the infant from infections.

Digestive functionColostrum stimulates digestive tract function and eases defecation. Easier to digest than formula milk.

CostBreastmilk is free and readily available as long as the mother remains healthy

BondingAids in mother-child bonding and communication

NutritionMore complete than formula and changes in composition to match the needs of the infant

Mothers healthAids in weight-loss, reduces risk of breast cancer, type II diabetes and post-partum depression.

A.3.3 Outline the causes and symptoms of type II diabetes.

Diabetes mellitus (type II diabetes) is also known as adult-onset diabetes as it generally manifests in adulthood. Receptors on the liver become resistant to insulin produced by the pancreas, leading to complications with blood sugar control. Causes: Obesity, and prolonged intake of high-energy foods can cause the receptors in the liver to wear out or become resistant to insulin. There is a very strong link with obesity. As the obesity epidemic increases, the age of adult-onset diabetes is also decreasing. Genetics also plays a role. Some people are genetically more susceptible to developing type II diabetes and should use their family history as an indicator and take preventative measures largely a balanced diet and exercise.

Symptoms:

Glucose in the urine as the kidney is unable to reabsorb all of the glucose back into the blood. Deyhdration as water-balance is disrupted, coupled with excessive urination. Weight loss as insulin is less able to store fat. Sleep loss and tiredness are also symptoms. Blurred vision and potential blindness. A.3.4 Explain the dietary advice that should be given to a patient who has developed type II diabetes.

Type II diabetes can be controlled through careful diet and healthy lifestyle. An obese or overweight patient would be advised to reduce their weight and exercise more.

Dietary advice: Explanation:

Eat low GI foods. Some foods release energy more slowly - they have a lower glyceimic index. Eating these reduces spikes in blood sugar.

Cut out sugars and refined carbohydratesThese are high GI foods they are broken down into sugars and absorbed quickly, causing blood sugar to rise quickly. They include sugary snacks, white bread and pasta.

Eat high fibre foodsHigh fibre makes one feel without providing too much energy. High fibre diets can also help reduce the effects of diabetes.

Small, regular mealsSmaller releases of energy more frequently result in less dramatic blood sugar changes than large, infrequent meals.

Choose diabetic alternativesSome packaged foods may be labeled to show that they have reduced sugars or carbohydrates, suitable for diabetics.

Read the food labelsLearn how to read and interpret food labels to avoid eating unsuitable foods.

A.3.5 Discuss the ethical issues concerning the eating of animal food products, including honey, eggs, milk and meat.

Animal products are a major component of the human diet, though they are not without their ethical concerns. As populations grow, demand for food increases, including meat and animal products. Concerns arise with regard to ethical treatment of animals and environmental sustainability. Food productAdvantagesEthical concerns

MeatSource of proteins, some vitamins and minerals. -Animal welfare issues in intensively-farmed cattle, poultry. Pain and suffering in slaughter.

-Growth of antibiotic-resistant bacteria and new strains of viruses as a result of overuse of medication. Use of growth hormones may affect human health, such as earlier onset of puberty.

-Huge demand for land and water to grow crops to feed animals is no longer sustainable and results in clearing of rainforests and habitat destruction. Methane and other emissions from farming livestock contribute to global warming.

FishSource of proteins and helpful fatty acids. -Many fish species are endangered due to overfishing.

-Concerns of biomagnification of toxins in the food chain and risks to human health.

MilkSource of energy, protein, calcium-Animal welfare issues in intensively-farmed cattle, poultry.

-Growth of antibiotic-resistant bacteria and new strains of viruses as a result of overuse of medication.

-Huge demand for land and water to grow crops to feed animals is no longer sustainable and results in clearing of rainforests and habitat destruction. Methane and other emissions from farming livestock contribute to global warming.

EggsSource of protein and fats, a meat alternative in some cultures- Cholesterol health risks associated with too much egg yolk consumption.

-Battery-farmed chickens fed hormones, in cramped conditions and can be treated inhumanely. Living spaces can be dirty and encourage spread of illness.

-Male chicks are routinely culled as they cannot produce eggs.

HoneyHoney is a natural sweetener. Bees pollinate many flower species. -Farmed bees compete with local insect and bee populations for nectar. Artificial selection of bees will result in a genetic shift in bee populations.

A.3.6 Evaluate the benefits of reducing dietary cholesterol in lowering the risk of coronary heart disease.

Cholesterol is needed in small amounts in the body to produce hormones and plasma membranes. In excess it is thought to contribute to atherosclerosis by forming deposits in the arteries. Rupture of plaques can cause clots, or CHD. However, this is a paradigm that is being challenged and it highlight the correlation-cause argument. In a review of studies, it has been suggested that the link between dietary cholesterol intake and CHD is not logical, and that the more likely cause of CHD is a diet high in saturated fats. Diets high in saturated fats tend to be high in cholesterol, so there is a correlation without necessarily causation.

With moderate cholesterol intake, the body is able to remove excess with no harmful effect dietary cholesterol is not necessarily converted into plasma cholesterol. Plasma cholesterol can be HDL (not harmful), or LDL (plaque-forming).

Extreme intakes may lead to a greater buildup of LDL in atherosclerosis. Although there is a small risk of cholesterol leading to CHD, the risks of smoking, inactivity and heredity are much stronger and more closely related to CHD.

Although a cholesterol-controlled diet may slow or reduce the risk of atherosclerosis, it must be combined with a healthy diet and lifestyle if it is to have a significant effect on reducing the risk of CHD.

A.3.7 Discuss the concept of food miles and the reasons for consumers choosing foods to minimize food miles.

Food miles are a measure of the distance a food product travels from plough to plate. It is an indicator of the environmental impact of the foods we eat, as this travel involves costs in fuel, emissions, packaging and time: the further a product travels, the less sustainable it is. Some imported foods cost more in energy per gram for their transport than they provide for the consumer.

Some consumers prefer to choose locally grown or farmed food products to reduce the costs, use of packaging and preservatives, use of oil/fuel and emissions. They may also hope to encourage outlets to use local providers of produce rather than imported goods. PAGE 14