Energy is the "fuel we run on" or, more formally, "the capacity to do work". Plants capture the sun's energy through photosynthesis and store it as glucose – the most basic chemical from which the 3 macronutrients (carbohydrates, protein, and fats) are made. By consuming plants and animals, we obtain these macronutrients which then provide us with energy as our body breaks them down.
Energy requirements are the dietary energy intake that is required to maintain balance in our bodies. This is obviously specific for each and every person and will depend on weight, height, age, gender and level of physical activity.
We measure the energy content of our food in kcal, or calories (technically a kilocalorie).
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Macronutrients
Each macronutrient provides a specific amount of energy (kcal) per one gram:
| Carbohydrates | 113 kcal per oz |
| Proteins | 113 kcal per oz |
| Fats | 264 kcal per oz |
| Alcohol | 205 kcal per oz |
Although alcohol is not a macronutrient, it can contribute so much to your overall energy intake that it's worth including here.
Daily Energy Requirements
The daily energy requirements are defined as the total amount of energy required for total energy expenditure (TEE) within 24 hours in order to maintain body weight.
The TEE is made up of 4 components:
- Diet Induced Thermogenesis (DIT)
- Physical Activity Energy Expenditure (PAEE)
- Growth Energy Expenditure (GEE) – for growing children
- Basal/Resting Energy Expenditure (BEE)
Diet Induced Thermogenesis (DIT):
Energy required for digestion of food and absorption, transport and oxidation of nutrients; 5-15% TEE
Physical Activity Energy Expenditure (PAEE):
Physical activity; 20% TEE, but can vary significantly from person to person.
Growth Energy Expenditure (GEE):
Energy required for the growth and development of children – this is a huge component of energy expenditure for a newborn, but rapidly tails off;
- 1 month: 40% TEE
- 1-3 months: 35% of TEE
- 3-6 months: 17.5% of TEE
- 6-9 months: 6% of TEE
- 9-12 months: 3% of TEE
- 1-2 years: <2% of TEE
- 2 years – adolescence: 1-2% of TEE
- Adolescence: 4%
Basal/Resting Energy Expenditure (BEE):
Minimum energy required to maintain the basic vital bodily functions; 50-70% of TEE
The BEE is usually estimated in one of two ways – using the Schofield formula or the Harris-Benedict formula.
These are useful if you want to get a little more scientific in estimating daily calorie needs, however if you're not a nutritionist, the below is sufficient and provides a good approximation.
0-12 Months
| Age (months) | Boys (kcal) | Girls (kcal) |
| 0 - 1 | 518 | 464 |
| 1 - 2 | 570 | 517 |
| 2 - 3 | 596 | 550 |
| 3 - 4 | 569 | 537 |
| 4 - 5 | 608 | 571 |
| 5 - 6 | 639 | 599 |
| 6 - 7 | 653 | 604 |
| 7 - 8 | 680 | 629 |
| 8 - 9 | 702 | 652 |
| 9 - 10 | 731 | 676 |
| 10 - 11 | 752 | 694 |
| 11 - 12 | 775 | 712 |
1-18 Years
| Age (years) | Boys (kcal) | Girls (kcal) |
| 1 - 2 | 950 | 850 |
| 2 - 3 | 1,125 | 1,050 |
| 3 - 4 | 1,250 | 1,150 |
| 4 - 5 | 1,350 | 1,250 |
| 5 - 6 | 1,475 | 1,325 |
| 6 - 7 | 1,575 | 1,425 |
| 7 - 8 | 1,700 | 1,550 |
| 8 - 9 | 1,825 | 1,700 |
| 9 - 10 | 1,975 | 1,850 |
| 10 - 11 | 2,150 | 2,000 |
| 11 - 12 | 2,350 | 2,150 |
| 12 - 13 | 2,550 | 2,275 |
| 13 - 14 | 2,775 | 2,375 |
| 14 - 15 | 3,000 | 2,450 |
| 15 - 16 | 3,175 | 2,500 |
| 16 - 17 | 3,325 | 2,500 |
| 17 - 18 | 3,400 | 2,500 |
Resources
- Frary CD, Johnson RK. Energy In: Mahan LK, Escott-Stump, S. Krause’s Food & Nutrition Therapy. International Edition, 12e. 2008. pg. 22-38.
- Pinheiro Volp AC, Esteves de Oliveira FC, Duarte Moreira Alves R, Esteves YJ Bressan EA. 2011. Energy expenditure: components and evaluation methods. Nutr Hosp. 26(3):430-440.
- Report of a Joint FAO/WHO/UNU Expert Consultation. Human energy requirements. 2001, Rome.
- Butte NF. 2015. Energy Requirements of Infants, Children and Adolescents. In: Koletzko B. editor, Pediatric Nutrition in Practice, Edition 2. Basel, pg. 33-40.