Kilojoules (kJ) are a unit of energy commonly used to measure the energy content in food and the energy expenditure of physical activities. One kilojoule is equal to 1,000 joules, which is a standard unit of energy in the International System of Units (SI). Understanding kilojoules helps individuals manage their diet and energy balance, as it indicates how much energy the body receives from food. In nutrition, the energy provided by food is often expressed in kilojoules to help people make informed choices about their diet. For example, a banana may contain around 400 kJ, while a slice of cake can have significantly more. Monitoring kilojoules can assist in maintaining a healthy lifestyle and achieving fitness goals.