GCSE Biology Revision
A healthy diet contains the right balance of the different foods your body needs and the right amount of energy. The following food groups are needed:
If your diet is not balanced you are malnourished. This may lead to you becoming overweight or underweight. It may also lead to deficiency diseases. The baby in the photograph is suffering from the deficiency disease kwashiorkor caused by insufficient protein in the diet. The thinning of the hair and swelling of the cheeks are signs of this. The swollen areas around the baby's lips are signs of vitamin B deficiency as well. An unbalanced diet can also lead to diseases such as type 2 diabetes.
If you take in more energy (from the food you eat) than is needed by the body you will gain body mass. Exercise increases the amount of energy used by the body so athletes will often have to eat more to maintain their body mass.
Around 1 in 7 people in the world today are either overweight (body mass index (BMI) of between 25 and 30) or obese (an obese person is very overweight with a BMI of more than 30). Find out more about this on the NHS website. Type 2 diabetes is associated with being overweight or obese. The more overweight you are the more likely you are going to get type 2 diabetes.
This is the rate at which chemical reactions in the cells of the body are carried out (in particular, respiration) and varies with the amount of activity you do and the proportion of muscle to fat you have in the body. For example, a person who has lots of muscle will have a higher metabolic rate than a person of equal weight who has more fat.
The less exercise you take and the warmer it is, the less food you need. People who exercise regularly are usually fitter than people who take little exercise. If you exercise your metabolic rate will normally remain high for some time after you have finished. People who exercise regularly are usually healthier than those who do little or no exercise. In particular, you are less likely to die prematurely, die prematurely from heart diesease and less likely to develop diabetes.
The graph on the left is taken from a scientific study by Dr Jonathan Myers. In this study he found that around 250 000 deaths per year in the United States are probably due to lack of exercise. The least fit people are around 4.5 times more likely to die prematurely than the most fit.
Your metabolic rate may be affected by inherited factors. Some people may have a slightly lower or slightly higher metabolic rate than average. Inherited factors may affect our health in other ways, for example the level of cholesterol in our blood.
There are many different types of slimming programme and you may be asked to interpret data about these. Many studies have shown that attending regular meetings, such as Weightwatchers, is the most effective way of losing weight. However, other slimming programmes such as the Atkins diet are just as effective. You may be given data to evaluate on this topic. Often the studies are short-term and there appears to be little data on the long-term effectiveness of various programmes. All of the slimming programmes are effectively reducing your energy intake. The Atkins diet achieves this through a reduction in the carbohydrate intake. In a major study the average weight loss achieved different types of slimming programme is shown in the graph below:
In this study all of the participants of the different slimming programmes achieved a significant reduction in their body mass compared to the control group (people not on a slimming programme).