Biology Unit 1 - Health, Food and Diet

In order to stay healthy, your diet must provide the energy you need, but not more.

Each of the food groups have different uses in the body, so the right balance of them is needed. You need:

• enough carbohydrates to release energy
• enough fats to keep warm and release energy
• enough protein for growth, cell repair and cell replacement
• enough fibre to keep everything moving slowly through the digestive system
• enough vitamins and minerals to keep your skin, bones and everything else generally healthy.

Energy is needed to fuel chemical reactions in the body (which keep us alive). The reactions are known as the metabolism, and the speed at which the reactions occur is called the metabolic rate.

Slight variations in the resting metabolic rate occur in different people. For example, muscle requires more energy than fatty tissue. Therefore people with a higher proportion of muscle to fat in their bodies - assuming all other factors are equal - have a higher metabolic rate.

Physically bigger people normally have a higher metabolic rate than smaller people as the bigger you are, the more energy your body requires.

This means that, generally speaking, men tend to have a higher metabolic rate than women due to them normally being physically bigger and typically having more muscle than women.

Genetic factors can also have an effect on metabolic rate.

Regular exercise can boost resting metabolic rate as it causes an increase in muscle.

When exercising, you need more energy, therefore your metabolic rate increases and stays high for some time afterwards.

People who have active jobs tend to need more energy on a daily basis, for example, builders normally need more energy than office workers.

Therefore, your activity level affects the amount of energy your diet should contain. If you do only a small amount of exercise, you don't require as much energy (fats and carbohydrates) as someone who does a lot of exercise.

People who have an unbalanced diet are said to be malnourished.

Malnourished people can be fat, thin or unhealthy in other ways.

Malnourishment is caused by eating too much, which can cause problems such as obesity, an increase in blood cholesteral, high blood pressure and heart problems.

Or it is caused by eating too little which can cause a variety of problems depending on what is missing from the person's diet. 

• Excess carbohydrate and/or fat in your diet can lead to obesity.
• It is a common disorder in well developed countries and defined as being 20% or more over the recommended body mass.
• Hormonal problems can also lead to obesity, though usual causes are bad diet, overheating and lack of exercise.
• Obesity can lead to arthritis (inflammation of the joints), type 2 diabetes (inability to control blood sugar level), high blood pressure and heart disease. It can also be a risk factor is some types of cancer.
• Too much saturated fat can increase blood cholesteral level.
• Eating too much salt can cause high blood pressure and heart problems.

• A lack of food is also unhealthy, and is particularly a problem in developing countries.
• Problems associated with it depend on what foods are missing from the diet. Common problems are slow growth (in children), fatigue, poor immune system, irregular periods (in women).
• Deficiency diseases are caused by a lack of vitamins or minerals. For example, scurvy is a deficiency disease caused by a lack of vitamin C and causes problems with the skin, joints and gums.

Regular exercise can help keep you healthy.

People who exercise regularly tend to be healthier than those who don't.

Exercise increases the amount of energy used in the body, so decreases the amount stored as fat.

Exercise also builds muscle which helps to boost your metabolic rate.

Therefore people who exercise are less likely to suffer from health problems like obesity.

However, sometimes people can be fit but not healthy. For example, they could be physically fit and slim but can be malnourised due to an unbalanced diet.

Inherited factors can affect your health as well as what you eat and what you do.

Some inherited factors can affect your metabolic rate. For example, some inherited factors cause an underactive thyroid glandm which can lower the metabolic rate and lead to obesity.

Some inherited factors can affect blood cholesterol levels. Cholesteral is a fatty substance which is essential for good health and is found in every cell in the body. Some inherited factors can increase blood cholesteral which increases the risk of heart disease.

There are lots of slimming products around and they all claim they'll help you lose weight.

Ways to tells if slimming products work:

• If the report is a scientific study (e.g. if it's published in a reputable journal)
• If it was written by a qualified person (not connected to the person selling it)
• If the sample of people tested was large enough to give reliable results
• If there have been other studies which found similar results.

To lose weight you really just need to take in less energy than you use:

• Eat less fat or carbohydrate (so you take in less energy), or
• do more exercise (so you use more energy)

Some claims may be true, but misleading. For example, low-fat bars may be low in fat, but eating them without changing the rest of your diet doesn't mean you'll lose weight, as you may still be taking too much energy.