Asleep, awake, eating, bathing, grooming, working or engaging in passionate pursuits, you need energy, which is supplied from your diet in the form of calories. Energy fuels your body’s internal functions, repairs, builds and maintains cells and body tissues, and supports the external activities that enable you to interact with the physical world. Water, your body’s most important nutrient, helps facilitate the chemical reactions that produce energy from food.
Basal metabolic rate, or BMR, is the minimal amount of energy needed to keep your body functioning and alive while at rest. BMR uses about 60 to 65 percent of daily energy stores, according to the University of Maryland School of Medicine. In the resting state, energy supports circulation, respiration, digestion, excretion and other functions performed by vital organs. Seven percent of your total energy supply keeps your body warm. Energy needs differ according to age, gender, body composition, health status, diet and activity level.
Body composition is one determinant of energy requirements. Muscle is the body’s most metabolic tissue, which means it requires more energy than other body tissues to maintain itself. Because they are naturally more muscular, men need more energy – calories – than women do. Children and young adults undergoing developmental changes in height, weight and body composition have greater energy needs. Energy requirements change as people age, because muscle tissue atrophies, causing a reduction in basal energy metabolism, according to the Colorado State University Extension website.
Digestion and Absorption
Digestion and absorption of the nutrients in food use 5 to 10 percent of your daily energy stores to produce more energy, according to the University of Maryland School of Medicine. Diet composition also determines energy requirements for food metabolism. Carbohydrates, protein and fats are digested at different rates. For example, the October 2004 issue of the “Journal of the American College of Nutrition” published a report stating animal protein takes longer to digest than carbohydrates or fat, and uses 20 to 35 percent of calories – energy – to complete the digestive process.
External functions supported by energy include exercise, work and play. If you are active and have a high lean body mass to fat ratio, your energy needs are greater than someone who leads a sedentary lifestyle or has a high body fat composition, according to Sheri Barke, MPH, RD, College of Canyons Student Health and Wellness Center. Fighting invading organisms that cause infection and disease uses massive amounts of physical energy. Fever drains energy stores to restore and maintain normal temperature balance. Resting metabolic rates increased by 8 percent in 25 study participants infected with respiratory tract infections, according to a report published in the July/August 2010 issue of the “American Journal of Human Biology.” Study results indicate even modest physiological responses to infection might cause substantial increases in energy usage.
Your brain needs a constant supply of energy to continuously maintain, support and protect your life. Mental activities, such as work, hobbies, reading, studying, homework, doing crossword puzzles, learning a new language, any mentally challenging endeavor, including daydreaming, requires energy. According to the Franklin Institute, brain cells require double the amount of energy needed by other cells. Worry and stress drain mental and physical energy. Problems with finances, employment, school, health, relationships, family and friends can increase susceptibility to illness, according to Purdue University Student Health Center.
- University of Maryland School of Medicine: How Much Energy Does Your Body Use?
- Colorado State University Extension: Nutrition and Aging
- Journal of the American College of Nutrition: The Effects of High Protein Diets on Thermogenesis, Satiety and Weight Loss: A Critical Review
- College of Canyons: Calories, What’s the Magical Formula to Achieve Your Weight Goals
- American Journal of Human Biology: Toward Quantifying the Usage Costs of Human Immunity: Altered Metabolic Rates and Hormone Levels During Acute Immune Activation in Men
- Franklin Institute: Nourish – Carbohydrates Fuel Your Brain
- Purdue University: Balancing Stress in the College Years
- Daydream image by Leticia Wilson from Fotolia.com