9.6 Balanced Diet
A balanced diet provides all seven classes of food in the correct proportions to meet individual metabolic needs and ensure optimal health.
Learning Objectives
- Define a balanced diet and list all seven classes of food.
- Define energy value and calculate the energy value in food samples using the standard formula.
- Conduct experiments to determine and compare the energy value of cashew nuts and groundnuts.
- Determine the vitamin C content in fruit juices and vegetable juice using DCPIP solution.
- Investigate the effect of ambient temperature on the vitamin C content of fruit juice.
- Explain the causes and effects of obesity, and evaluate diet modifications for specific individuals, such as obese individuals and cancer patients.
Simple Calorimeter Setup for Energy Value Determination
To illustrate the experimental arrangement for measuring the heat energy released during combustion of food.
Boiling tube
Holds 20 ml of distilled water above the burning food sample.
Thermometer
Measures the rise in water temperature during combustion.
Wind barrier
Reduces heat loss to the surroundings during the experiment.
Short Explanation
Definition of a Balanced Diet
A balanced diet refers to a diet consisting of all seven food classes: carbohydrates, lipids, proteins, vitamins, mineral salts, fibre, and water in the correct proportion and balanced quantity according to individual needs so that optimal health can be maintained.
Energy value
The energy value is the total amount of energy released when one gram of food is oxidised completely. It is measured in kilojoule per gram, \(\text{kJ g}^{-1}\).
Calorie and joule
\(1\text{ calorie} = 4.2\text{ joule (J)}\) and \(1\text{ kilojoule (kJ)} = 1000\text{ joule (J)}\). The specific heat capacity of water is \(4.2\text{ J g}^{-1}\text{ }^\circ\text{C}^{-1}\).
Energy value formula
\[\text{Energy value of food (kJ g}^{-1}\text{)} = \frac{\text{Water mass (g)} \times 4.2\text{ J g}^{-1}\text{ }^\circ\text{C}^{-1} \times \text{Increase in water temperature (}^\circ\text{C)}}{\text{Mass of food sample (g)} \times 1000}\]
1 calorie definition
1 calorie (or 4.2 J) is the quantity of heat energy needed to raise the temperature of \(1\text{ gram}\) of water by \(1\text{ }^\circ\text{C}\) at a pressure of 1 standard atmosphere.
Activity 9.4: Studying the Energy Value of Food Samples
Problem statement: Which food sample has the highest energy value?
Hypothesis: Groundnuts have a higher energy value compared to cashew nuts.
Variables:
- Manipulated: Types of food samples (cashew nuts, groundnuts).
- Responding: Energy value of food sample.
- Fixed: Water mass.
Procedure outline:
- Weigh food sample with an electronic balance.
- Measure \(20\text{ ml}\) of distilled water into a boiling tube (\(20\text{ ml} = 20\text{ g}\)).
- Clamp the boiling tube, insert thermometer, fix position with cotton wool, and record initial temperature.
- Fix food sample on a needle held upright by plasticine; place barrier around apparatus.
- Ignite food sample using Bunsen burner and position directly below boiling tube.
- Stir water slowly and record highest temperature reached after complete combustion.
- Calculate energy value using the formula.
Activity 9.5: Determining the Contents of Vitamin C in Fruit and Vegetable Juices
Principle: Ascorbic acid reduces and decolourises 1% blue DCPIP (dichlorophenolindophenol) solution.
Materials: Orange juice, lime juice, fresh carrot juice, 0.1% ascorbic acid solution, 1% DCPIP solution, distilled water.
Formulas:
\[\text{Percentage of vitamin C} = \frac{\text{Volume of 0.1\% ascorbic acid solution}}{\text{Volume of juice used}} \times 0.1\%\]
\[\text{Vitamin C concentration (mg ml}^{-1}\text{)} = \frac{\text{Volume of ascorbic acid solution}}{\text{Volume of juice used}} \times 1.0\%\]
Procedure outline:
- Place \(1\text{ ml}\) of 1% DCPIP solution in a specimen tube.
- Fill a syringe with 0.1% ascorbic acid solution without trapping air bubbles.
- Drip drop by drop into DCPIP solution while stirring gently until the blue colour decolourises.
- Record the volume required; repeat with fruit/vegetable juices to calculate and compare concentrations.
Activity 9.6: Studying the Effect of Temperature on Vitamin C in Orange Juice
Problem statement: What is the most suitable ambient temperature to keep orange juice?
Hypothesis: Orange juice stored at a low ambient temperature has the highest content of vitamin C.
Variables:
- Manipulated: Ambient temperature (soaked in ice, room temperature, boiling water for 30 minutes).
- Responding: Volume of orange juice required to decolourise DCPIP solution.
- Fixed: Volume of DCPIP solution.
Precaution: Juice must not be exposed too long to air to avoid oxidation.
Finding/Principle: High temperature causes loss/destruction of vitamin C. Fruits and vegetables must be kept at a suitable low temperature range to preserve vitamin C.
Diet Modifications for Specific Individuals
Individual balanced diets vary according to lifestyle, health conditions, and specific nutritional requirements.
Pinggan Sihat Malaysia (Malaysian Healthy Plate) illustrates relative quantities of various food classes in a balanced meal (quarter-quarter-half concept).
Obesity:
- Cause: Storage of excess fats as a result of imbalanced food intake and energy expenditure.
- Dietary management: Reduce intake of carbohydrates and fats; increase intake of vegetables and fruits.
- Risks of unchecked high saturated fat/cholesterol diet: Diabetes mellitus, cardiovascular diseases such as atherosclerosis and hypertension, potentially resulting in myocardial infarction (heart attack) or stroke.
Cancer patients: Diet modification during cancer treatment must ensure sufficient energy, reduce the risk of infections, and enable quick recovery.
Millennial Career: Nutritionists are specialists in the field of nutrition who advise individuals on suitable diets.
Try to Answer First
Answer in your mind, then press “Check Answer”.
State the seven food classes that make up a balanced diet.
What is the definition of energy value of food?
Why is orange juice exposed to high temperatures required in larger volumes to decolourise \(1\text{ ml}\) of DCPIP solution?
Common Mistakes
- Forgetting to convert the denominator mass or energy from J to kJ by omitting the division by 1000 in the energy value formula.
- Failing to use a wind barrier or stirring the water slowly during calorimeter experiments, causing substantial heat loss and uneven temperature readings.
- Assuming that \(1\text{ ml}\) of water does not equal \(1\text{ g}\) of water (since water density is \(1\text{ g ml}^{-1}\), \(20\text{ ml}\) equals \(20\text{ g}\)).
- Shaking or exposing fruit juice to air for too long during DCPIP testing, causing atmospheric oxidation of ascorbic acid before titration.
Concept Misunderstandings
A balanced diet means eating equal amounts of every food class.
A balanced diet requires all seven food classes in the correct proportions and balanced quantities tailored to an individual's lifestyle, health condition, and metabolic requirements.
Experimental energy values match theoretical values on nutrition labels.
Experimental values from simple laboratory calorimeters are lower than theoretical values due to heat loss to surroundings, incomplete combustion of food, and heat absorption by the glass boiling tube.
Summary
- A balanced diet contains carbohydrates, lipids, proteins, vitamins, mineral salts, fibre, and water in appropriate proportions.
- Energy value (\(\text{kJ g}^{-1}\)) measures heat released per gram of oxidised food: \(\frac{\text{Water mass (g)} \times 4.2 \times \Delta T}{\text{Food mass (g)} \times 1000}\).
- Vitamin C content is determined by titrating fruit/vegetable juice against blue DCPIP solution until decolourised.
- Vitamin C is unstable and degrades at high temperatures; low ambient temperatures best preserve vitamin C content.
- Obesity stems from excess fat storage due to energy imbalance; management involves cutting carbohydrates and fats while raising fruit/vegetable intake to prevent atherosclerosis, hypertension, stroke, or heart attacks.
Short Activity
Objective: test your understanding of balanced diet, energy value, vitamin C and diet modifications.
A. Objective Quiz
What is the quantity of heat energy needed to raise the temperature of 1 gram of water by \(1\text{ }^\circ\text{C}\) at 1 standard atmosphere?
What is the function of the cotton wool at the mouth of the boiling tube in the energy value experiment?
B. Fill in the Blanks
Obesity is caused by the storage of excess as a result of imbalanced food intake and use of energy.
In the experiment to determine vitamin C, ascorbic acid decolourises the blue colour of solution.
C. Matching / Drag and Drop
Match each individual condition or term with its corresponding dietary modification or definition. On a phone, tap a choice first, then tap the matching box. Tap the Answer Choices area to return a selected item.
C. Match the Term / Condition to Its Dietary Modification / Description
Write the correct term next to each description.
| Dietary Modification / Description | Term / Condition |
|---|---|
| 1. Reduce intake of carbohydrates and saturated fats, increase fruits and vegetables | |
| 2. Modify diet to provide sufficient energy, reduce infection risk, and aid quick recovery | |
| 3. Illustrates the relative quantity of various food classes in a balanced meal | |
| 4. Specialist in the field of nutrition who advises individuals on suitable diets |
Answer choices: Obese individual • Cancer patient • Pinggan Sihat Malaysia • Nutritionist
