2.1 Balanced Diet and Calorific Value

Balanced Diet and Pinggan Sihat Malaysia

• A balanced diet includes all classes of food in the right quantity according to an individual’s body requirement.
• A lack or an excess of any class of food causes malnutrition. Examples include goitre, scurvy, marasmus, kwashiorkor and rickets.
• Pinggan Sihat Malaysia divides one plate into:
  • Half: fruits and vegetables.
  • One quarter: rice or other carbohydrate sources.
  • One quarter: fish or other protein sources.
• Daily applications:
  • Eat three healthy main meals a day.
  • Eat one or two healthy snacks between meals if needed.
  • Eat more cereal foods.
  • Eat less fried food or food containing coconut milk.
  • Eat home-cooked food more frequently.

Calorific Value of Food

• Calorific value, or energy value, is the amount of energy released from the complete oxidation or combustion of 1 g of food.
• Energy is measured in calorie (cal), kilocalorie (kcal), joule (J) or kilojoule (kJ).

$1\text{cal}=4.2\text{J}$

$1\text{kcal}=4200\text{J}=4.2\text{kJ}$

• The S.I. unit for calorific value is joule per kilogram, ${\text{J kg}}^{-1}$.
• A bomb calorimeter measures the calorific value of food accurately.
• The calorific value of food depends on its quantities of carbohydrate, protein and fat.

Class of food	Calorific value (${\text{kJ g}}^{-1}$)
Carbohydrate	16.7
Fat	37.6
Protein	16.7

Examples of estimated calorific values:

Food	Calorific value (${\text{kJ g}}^{-1}$)
Rice	15.04
White bread	10.60
Coarse sugar	16.50
Palm oil	38.00
Butter	31.20
Chicken	8.27
Beef	13.11
Cabbage	0.34
Cucumber	0.55

Experiment 2.1: Estimating Calorific Value

Aim: Estimate the calorific value of groundnuts, anchovies and bread using a calorimeter.

Problem statement: Which food sample has the highest calorific value?

Hypothesis: The calorific value of groundnuts is higher than that of bread and anchovies.

Variables:

• Manipulated: type of food sample.
• Responding: change in temperature / calorific value of food.
• Constant: mass of water.

Materials: 1 g each of groundnuts, bread and anchovies, cotton wool and distilled water.

Apparatus: Retort stand, boiling tube, thermometer, shield, plasticine and needle.

Apparatus arrangement: A food sample fixed on a needle is burnt below a boiling tube containing distilled water. A thermometer measures the water temperature; a shield reduces heat loss.

Procedure:

1. Set up the apparatus.
2. Record the type and mass of food, mass of water and initial temperature, $T_1$.
3. Set the food sample alight.
4. Record the final temperature, $T_2$, after the sample burns completely.
5. Repeat with the other food samples using the same mass of water.

$\text{Change in temperature}=T_2-T_1$

• The experimental value is smaller than the actual value because some heat energy is lost to the surroundings.
• Suitable samples: rice or bread for carbohydrate, groundnut or palm oil for fat, and anchovy or egg white for protein.
• Water has no calorific value because it cannot be completely oxidised or burnt.

Effects of Calorie Intake That Does Not Meet Individual Requirements

• Total calories from meals must meet individual requirements.
• Insufficient intake may cause underweight and malnutrition.
• Excessive intake may cause obesity.
• Inappropriate mealtimes and unhealthy eating patterns may cause malnutrition, obesity, anorexia nervosa, arteriosclerosis, diabetes mellitus, high blood pressure, thrombosis, stroke, heart attack and heart disease.

Health problem	Cause and effect
Obesity	Excessive intake of high-calorific food over a long period increases the risk of diabetes mellitus, arteriosclerosis and high blood pressure.
Anorexia nervosa	Refusal to eat due to fear of gaining weight causes malnutrition that can be fatal.
Atherosclerosis	Cholesterol deposits on artery walls narrow the artery lumen, causing high blood pressure and increasing the risk of heart disease and stroke.
Diabetes mellitus	Long-term intake of food and drinks high in sugar affects vision, kidneys and the nervous system, and slows wound healing.
High blood pressure	Long-term intake of food high in salt increases the risk of heart disease and stroke.

Eating Patterns and Health

• Health depends on both the total calorie intake and eating patterns, including mealtimes and types of food.
• Fast food and junk food may contain:
  • Excess sugar: obesity, tooth decay and increased risk of early diabetes mellitus.
  • No beneficial nutrients: malnutrition.
  • Caffeine in carbonated drinks: insomnia, anxiety and addiction.
  • Artificial colouring and sweeteners: cancer, infertility, diabetes mellitus, and liver and kidney damage.
  • Excess salt: high blood pressure, heart disease and kidney damage.
• Twenty-four-hour restaurants, fast-food restaurants and junk-food advertising can encourage unsuitable mealtimes and excessive intake of unhealthy food.