Can you define the term "balanced diet" in AS/A-level Biology?
Balanced Diet
- A balanced diet is a diet that contains appropriate amounts of all necessary nutrients required for healthy growth and activity, including:
- Carbohydrates – for energy.
- Fats – for energy and insulation.
- Proteins – for growth and repair.
- Fibre – helps with the digestive system.
- Minerals/Vitamins – essential for body functions/chemical processes.
- Water – essential for body function and for transport.
- Consumption of an unbalanced diet can lead to malnutrition.
Health
- Having a good nutrition.
- Being free from disease.
- Having a good well-being (physical, mental and social).
- Having suitable housing.
Malnutrition
Malnutrition is having a lack of proper nutrition, caused by not an unbalanced diet – not having enough to eat or not eating enough of the right things.
Obesity
- Obesity is when a person’s body weight is 20% or more than the recommended weight for their height.
- It is caused by:
- Eating too much.
- Doing insufficient exercise.
- Energy intake is more than energy use.
- Having an unbalanced diet consisting mostly of fats, sugars, carbohydrates and alcohol.
- Obesity is thought to be the most important dietary factor in the following health problems:
- Cancer
- Cardiovascular disease
- Type 2 diabetes
We can measure whether a person is obese or not by using their BMI (Body Mass Index):
BMI = mass (in kg)/(height in m)2
Problems with BMI
Why might someone be placed in the wrong health category based on BMI score?
- There are differences between male and female.
- Women have a higher percentage of body fat.
- A woman may be pregnant. - BMI does not measure actual fat.
- The person may have more/less muscle/bone than normal.
- Muscle/bone is heavier than fat.
- BMI is only for adults.
Links between Diet and Coronary Heart Disease
Coronary heart disease (CHD) is the result of atherosclerosis.
Atherosclerosis is the deposition of fatty substances in the walls of coronary arteries.
It narrows the size of the lumen restricting blood flow to the heart muscle, which may cause oxygen starvation.
The endothelium (inner lining) of the artery can become damaged.
The damage is repaired by of white blood cells (phagocytes) encouraging the growth of smooth muscle and the deposition of fatty substances.
The deposits (atheromas) include cholesterol from low-density lipoproteins (tiny balls of fat and protein that are used to transport cholesterol around in the blood), fibre, dead blood cells and platelets.
The build-up of atheromas occurs under the endothelium, in the wall of the artery.
It eventually forms a plaque, which sticks out into the lumen of the artery, leaving the artery wall rougher and less flexible as well as creating a narrower lumen, reducing blood flow.
Decreasing the risk of CHD
- Eating more fibre.
- Consuming alcohol moderately.
- Eating oily fish.
Increasing the risk of CHD
- Eating excess salt – decreases the water potential of blood so more water is held in the blood and the blood pressure increases leading to hypertension which can damage the inner lining of arteries leading to atherosclerosis.
- Eating saturated fats.
- Eating more cholesterol.
When it comes to AS/A-level Biology, can you differentiate high-density lipoproteins (HDL) and low-density lipoproteins (LDL)?
Cholesterol
- Cholesterol is essential to the normal functioning of the body.
- They are found in cell membranes to improve stability and used to make steroid sex hormones and bile.
- Cholesterol must be transported around the body, however it is not soluble in water so must first be converted to a form that will mix with water.
- It is transported in the form of lipoproteins (tiny balls of fat combined with protein).
- There are two types of lipoprotein: high-density lipoproteins (HDL) and low-density lipoproteins (LDL).
- They are both released into the blood and can be taken up by cells that have the correct receptor sites.
- We do not eat lipoproteins, but our diet has a significant effect on the lipoprotein concentration in our blood.
- LDLs are associated with greater deposition in the artery walls so is best to maintain a low proportion of LDLs.
- HDLs are associated with reduced deposition in the artery walls so is best maintain a high proportion of HDLs in our blood.
- Eating saturated (animal) fats will increase the concentration of LDLs
- Eating a low-fat diet will reduce the overall concentration of lipoproteins
- Eating unsaturated fats increases the concentration of HDLs
- Eating polyunsaturated fats reduces the concentration of LDLs
- Eating monounsaturated fats reduces the concentration of LDLs
Drafted by Bonnie (Biology)