9.6 - Balanced Diet

Concept of a Balanced Diet

• A balanced diet contains all seven food classes—carbohydrates, lipids, proteins, vitamins, mineral salts, fibre and water—in correct proportions and balanced quantities according to individual needs for optimal health.

Determination of Energy Value in Food Samples

• Energy value: Total energy released when one gram of food is completely oxidised.
• Unit: kilojoule per gram (${\text{kJ g}}^{-1}$).
• $1\text{ calorie}=4.2\text{ joules}$; $1\text{ kilojoule}=1000\text{ joules}$.

Food-Calorimetry Experiment

• Burn a weighed food sample beneath a boiling tube containing a known mass of distilled water.
• Record the initial and highest water temperatures.
• Keep the water mass fixed when comparing food samples.

$\text{Energy value }({\text{kJ g}}^{-1})=\frac{\text{Water mass (g)}\times 4.2{\text{ J g}}^{-1}{}^{\circ }{\text{C}}^{-1}\times \text{temperature increase }({}^{\circ }\text{C})}{\text{food mass (g)}\times 1000}$

Determination of Vitamin C Content in Fruit or Vegetable Juices

• DCPIP is blue and is decolourised by vitamin C.
• Add $0.1\%$ ascorbic acid solution to $1\text{ ml}$ of $1\%$ DCPIP until decolourised; record the volume.
• Repeat with each fruit or vegetable juice, using the same DCPIP concentration and volume.
• A smaller juice volume needed to decolourise DCPIP indicates a higher vitamin C content.

$\text{Percentage of vitamin C}=\frac{\text{volume of ascorbic acid solution}}{\text{volume of juice used}}\times 0.1\%$

$\text{Vitamin C concentration }({\text{mg ml}}^{-1})=\frac{\text{volume of ascorbic acid solution}}{\text{volume of juice used}}\times 1.0\%$

• Low-temperature storage preserves more vitamin C; prolonged exposure and high temperature reduce vitamin C content.

Diet Modifications for Specific Individuals

• A balanced diet varies with lifestyle, health condition and nutritional requirements.
• Obesity: Reduce carbohydrates and fats; increase vegetables and fruits.
• Excess saturated fats and cholesterol increase the risk of diabetes mellitus and cardiovascular diseases such as atherosclerosis and hypertension, which may cause myocardial infarction or stroke.
• Cancer treatment: Modify diet to provide sufficient energy, reduce infection risk and speed recovery.
• Pinggan Sihat Malaysia shows the relative quantities of food classes in a balanced diet.