Key facts on food and diet
Food provides chemical energy that is released during respiration to support processes like movement, growth and repair.
A balanced diet includes carbohydrates, fats, proteins, vitamins, minerals, fibre and water, each with specific roles in the body.
Energy requirements vary depending on factors such as age, sex and activity level.
Poor diet and excess energy intake can lead to health problems like obesity, heart disease and stroke.
Practical B2 - How to investigate the energy content of food
A simple investigation can be conducted to investigate the energy content of a food sample.
Method
- Add 20cm³ of water to a boiling tube in a retort stand.
- Record the starting temperature.
- Ignite 1g of food on a mounted needle.
- Hold the burning food under the boiling tube until fully burned (relight if needed).
- Record the final water temperature.
- Record results in a table.
- Repeat steps 1-6 with different foods.
Example of Results:
| Food | At start (°C) | At end | Difference |
|---|---|---|---|
| Corn crisps | 20 | 42 | 22 |
| Potato crisps | 20 | 36 | 16 |
Conclusion:
The corn crisps had a larger increase in temperature meaning they have more energy than the potato crisps.
Sources of error:
The results obtained from this experiment are usually lower than the actual energy content of the food because:
- the entire food sample may not be burned
- some energy is lost to the air
- some is used to heat the glass of the boiling tube
Improvements:
- Stir water: stirring ensures even heat distribution.
Variables
- Independent variable: type of food.
- Dependent variable: temperature / °C.
- Controlled variables: mass of food, volume of water, distance of burning food from boiling tube.
How much energy do we need?
The following factors affect our energy needs:
- Age - young people/teenagers need more energy due to growth and development.
- Sex - males need more energy than females as they have more muscle.
- Activity - active people need more energy as their muscles are working harder.
Biological molecules
| Food | Function | Source |
|---|---|---|
| Carbohydrate | Energy source: starch (slow release) and sugar (fast release) | Bread, pasta, biscuits |
| Fat | Energy source, insulation | Oil, butter |
| Protein | Growth and repair | Red meat, eggs |
| Water | Solvent and transport of substances around the body | Most foods and drinks |
| Fibre | Prevent constipation | Wholemeal bread, fruit and vegetables |
| Vitamin C | Healthy teeth and gums. | Citrus fruits |
| Vitamin D | Strong bones and teeth. | Fish oil, dairy products |
| Calcium (mineral) | Strong bones and teeth | Dairy products |
| Iron (mineral) | Helps red blood cells carry oxygen | Red meat, spinach |
Food tests
| Food sample | Reagent | Method | Initial colour | Colour of positive result |
|---|---|---|---|---|
| Reducing sugar | Benedict’s | Add Benedict’s reagent to the food and boil in a water bath. | Blue | Brick red precipitate |
| Starch | Iodine | Add iodine reagent to the food. | Yellow-brown | Blue-black |
| Protein/amino acids | Biuret (a mixture of sodium hydroxide and copper sulfate). | Add Biuret reagent to the food. | Blue | Lilac/purple |
| Fat | Ethanol | Add ethanol to the food to dissolve the fat then add water. | Clear | White emulsion |
Food and health
There is a clear relationship between food and health. The following conditions are linked to diet and nutrition:
- obesity
- heart disease
- stroke
Obesity
When someone takes in more energy than they use, they become overweight and eventually obese. This can lead to a higher chance of heart disease and stroke.
Heart disease
A build-up of cholesterol, in the coronary arteries, causes heart disease. The coronary arteries become blocked and the heart muscle is starved of glucose and oxygen. Respiration cannot happen and the heart muscle dies.
Stroke
A build-up of cholesterol, in an artery in the brain, causes a stroke. The artery becomes blocked and the brain is starved of glucose and oxygen. Respiration cannot happen and brain cells die.
Reducing the risk of heart disease and stroke
Lifestyle changes:
- increase exercise
- reduce stress
- stop smoking
Diet changes:
- reduce salt intake
- reduce saturated fat intake
- reduce cholesterol
Costs to society
- medical costs – medicine and highly trained staff are expensive
- effect on family – increased stress due to a sick relative and reduced income if the relative is unable to work
- effect on society – working age people unable to work. This can cost society a lot of money.
Respiration
Respiration needs glucose and oxygen which is carried in the blood to the muscles.
Why is exercise so beneficial?
During exercise, muscles contract more and require more energy, which is released through respiration. To meet this demand, the blood flow to the muscles increases, raising the pulse rate (heart rate).
Regular exercise is beneficial as it:
- strengthens the heart muscle
- increases cardiac output when at rest – lower pulse rate
- reduces chance of a heart attack
- reduces the recovery rate (time taken for heart rate to return to normal after exercise)
Respiration
Respiration is an reaction that occurs in all cells to release energy.
This energy can then be used for:
- heat
- movement
- growth
- reproduction
Word equation
Glucose + oxygen → carbon dioxide + water + energy
Balanced symbol equation
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy