Body's Energy Demands
Macronutrients in our diet power the body, offering the necessary energy for its intricate systems to function effectively. Energy known as metabolic rate is produced in the body as a result of chemical processes, providing fuel to the body's complex mechanical, electrical, and chemical systems.
Comprehending Metabolic Rates
The amount of energy the body needs for resting, awake, and fasting states, maintaining a comfortably warm environment, is referred to as the resting metabolic rate (RMR). RMR varies from individual to individual due to various factors, including:
- Total daily energy expenditure: The breakdown of total daily energy expenditure reveals the three primary components: resting metabolic rate, physical activity, and the thermic effect of food.
- Sex: Males have a faster energy release rate than females, with males expenditure from food approximately 5-7% higher than females.
- Size: As the body's surface area increases, so too does the RMR.
- Body Composition: The more lean tissue a person has compared to fat tissue, the higher their RMR.
- Thyroid Hormone: Thyroid hormone stimulates resting metabolism. Too little thyroid hormone may lead to a drop in RMR.
- Age: The younger the individual, the higher the RMR for their size and gender.
- Other factors: Fever, certain drugs like caffeine, pregnancy, lactation, and emotions can increase the RMR.
For a 12-14-year-old boy of average height and weight, the RMR is roughly 6,500 kilojoules per day. For a girl of similar age, the RMR amounts to about 5,500 kilojoules per day.
RMR
The total metabolic rate represents the entirety of the energy utilized by the body to carry out its activities, often expressed in kilojoules per day.
= (10 x 60) + (6.25 x 165) - (5 x 14) + 5
The factors determining the total metabolic rate are:
- Resting metabolic rate
- Muscular work energy (suitable for activities as minimal as sitting to as intense as strenuous labor or exercise)
- The thermic effect of food
= 600 + 1,031.25 - 70 + 5
Foods like carbohydrates and fats have a thermic effect of around 5%, while protein exhibits a thermic effect of roughly 30%. For example, to metabolize 100 kilojoules of carbohydrate, the body requires 5 kilojoules for metabolization, leaving behind 95 kilojoules of usable energy. In comparison, processing 100 kilojoules of protein requires 30 kilojoules, leaving the body with 70 kilojoules of energy.
On average for a mildly active person, roughly 60% of total daily energy expenditure results from resting metabolism, around 32% stems from physical activity, and another 8% originates from the thermic effect of food. For a boy and girl with RMRs as outlined, this means their total metabolic rates are around 11,000 and 9,200 kilojoules per day, respectively.
= 1,566.25 calories x 4.18 to convert to kilojoules
Dietary Needs of Adolescents
A well-balanced adolescent diet should consist of essential components, with healthy eating practices in mind, such as consuming plenty of fresh fruits and vegetables, ensuring proper hydration, avoiding skipping meals, and refraining from regular consumption of energy drinks high in caffeine.
= 6,546.9kJ per day
Calculating Resting Metabolism Rate
The Mifflin equation can estimate resting metabolic rate (RMR) fairly accurately, taking into account weight, height, age, and sex. While this equation does not take into account ethnicity or the percentage of fat tissue to lean tissue, it remains an effective predictive tool.
The formula is as follows:
- For men: RMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
- For women: RMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
RMR
Using this formula for a teenage boy of 60 kg, 165 cm, and 14 years:
= (10 x 50) + (6.25 x 163) - (5 x 14) - 161
RMR = (10 x 60) + (6.25 x 165) - (5 x 14) + 5RMR = 600 + 1,031.25 - 70 + 5RMR = 1,566.25 calories * 4.18 (to convert to kilojoules)RMR = 6,546.9kJ per day
For a teenage girl of 50 kg, 163 cm, and 14 years, the calculations are as follows:
= 500 + 1,018.75 - 70 - 161
RMR = (10 x 50) + (6.25 x 163) - (5 x 14) - 161RMR = 500 + 1,018.75 - 70 - 161RMR = 1,287.75 calories * 4.18 (to convert to kilojoules)RMR = 5,382.8 kJ per day
Balancing Energy Intake and Energy Output
= 1,287.75 calories x 4.18 to convert to kilojoules
Balanced energy intake through nutritious foods with output through resting metabolism, exercise, growth, and digestion is essential for maintaining health and wellbeing. Achieving this balance can help maintain a positive energy balance in children and adolescents, promoting healthy growth and development.
For adults, maintaining energy balance by ensuring sufficient energy intake with calorie-burning activities is crucial for preserving health and wellbeing.
= 5,382.8 kJ per day
Important Links
For further information:
- Eat for Health: An energy requirements calculator is available at this site.
- HealthEd provides public health resources from leading New Zealand health organizations, including resources on healthy eating for young people and nutritional guidelines for children aged 2-12.
- Incorporating various elements of health and wellness, a balanced adolescent diet should encompass essential components such as maintaining proper hydration, consuming fresh fruits and vegetables, and avoiding skipping meals. Additionally, it's crucial to consider the impact of macronutrients ( carbohydrates, fats, and proteins) on metabolic rate as their thermic effect influences the energy expenditure.
- Engaging in both fitness and exercise activities can significantly contribute to the total metabolic rate, as it accounts for energy used during physical activities besides resting metabolism and thermic effect of food. Furthermore, proper nutrition, including the correct balance of macronutrients, strengthens the body's system, supporting optimal energy production for both health and wellness, and fitness-and-exercise.
