A Balanced Diet
All organisms require food to survive. It provide energy and the raw materials for growth. We take our food in ready-made as complicated organic molecules. These food molecules can be placed into seven main groups.
A balanced diet needs the correct amounts of each of these types of food molecules.
- Carbohydrates- these are made up of starch and sugars, e.g.glucose and are used in the body to supply or store energy.
- Fats- these are made up of fatty acids and glycerol, and are a rich store of energy.
- Proteins- these are made up of long chains and amino acids, they are used to help growth and repair in the body.
- Minerals- these are made up of different elements, e.g.iron and iron is used to make haemoglobin.
- Vitamins- these are made up of different structures, e.g.vitamin C and prevent scurvy.
- Fibre- is made up of cellulose and prevents constipation
- Water- is only water and all chemical reactions take place in water.
The exact amount of each substance that is needed in a balanced diet will vary. It depends on how old the person is, whether they are male or female and how active they are.
For example, teenagers need a high-protein diet to provide raw materials for growth. You can estimate the recommended daily average (RDA) protein intake for a person using the formula:
RDA in g = 0.75 x body mass in kg
However, it is not only the amount of protein that is important but also the type. Proteins from animals are called first class proteins because they contain more variety of amino acids compared with plant proteins.
Some people's diet may be influenced by other factors than just their daily requirements. Some people may be vegetarians or vegans and some religions require certain diets to be followed. Some people may have to avoid certain foods to prevent them becoming ill.
Digestion and Absorption
The job of the digestive system is to break down large food molecules. This is called digestion.
Digestion happens in two main ways: physical and chemical. Physical digestion occurs in the mouth where the teeth break up the food into smaller pieces.
Chemical digestion is caused by digestive enzymes (biological catalysts found in all cells of the body) that are released at various points along the digestive system.
- Saliva is released into the mouth from the salivary glands. It contains amylase to digest starch to maltose.
- The stomach makes gastric juice, containing hydrochloric acid. The acid kills microbes and creates the best pH for the protease to digest proteins.
- The liver makes bile that contains bile salts. They break the large fat droplets down into smaller droplets. Bile is stored in the gall bladder.
- The pancreas makes more protease and amylase. It also makes lipase to digest the fats to fatty acids and glycerol.
- The small intestine makes enzymes such as maltase. This digests maltose to glucose.
One the food molecules have been digested, they are small enough to diffuse into the bloodstream, or lymph vessels. This is called absorption.
This is the rate at which all the chemical reactions in the cells of the body are carried out. It varies with...
- the amount of activity you do - your metabolic rate increases with the amount of exercise you do and it stays high for some time after you have finished exercising.
- the proportion of fat to muscle in your body
- your family history - it can be affected by inherited factors.
People who exercise regularly are usually fitter than those who do not.
The less exercise you take the warmer it is, the less food you need.
A person is malnourished if their diet is not balanced. A poor diet can lead to...
- a person being too fat or too thin
- deficiency diseases, for example, scurvy, which is caused by lack of vitamin C.
In the developed world (e.g.UK,USA) people are consuming too much food and are taking too little exercise. The result in high levels of obesity and diseases linked to excess weight, such as...
- Arthritis (worn joints)
- Diabetes (high blood sugar)
- High Blood Pressure
- Heart Disease
In the developing world (e.g.some parts of Africa and Asia) people suffer from problems linked to lack of food, such as...
- Reduced resistance to infection
- Irregular periods in women
Cholesterol is naturally made in the liver and is the blood. Diet and inheritance factors affect how much cholesterol the liver makes.
Cholesterol is carried around the body by chemicals called lipoproteins (made from fat/lipid and protein). High levels of low-density cholesterol (bad cholesterol) in the blood increase the risk of disease of the heart and blood vessels.
· Low-density lipoproteins (LDLs) can cause heart disease.
· High-density lipoproteins (HDLs) are good cholesterols.
The balance of these is important for a healthy heart.
Too much salt in the diet can lead to increased blood pressure. So you shouold...
- eat less salt
- eat less processed food, which often contains a high proportion of fat and/or salt
- eat less saturated fats e.g.butter, animal fat (these increase blood cholesterol)
- eat more unsaturated fats (monounsaturated and polyunsaturated fat) e.g. vegetable oil, some fish. These help to reduce blood cholesterol levels and improve the balance between good and bad lipoproteins.
What are Statins?
Statins are drugs that work in the liver to reduce the chance of having a heart attack or a stroke by up to a third, and can increase the life expectancy of a person with a history of high choleserol when taken long term.