What Is Energy Used For Humans?

Energy is the capacity to do work and move matter. It is essential for all physiological functions and life itself. Energy enables our bodies to grow, reproduce, maintain body temperature, move, and react to the environment. Without energy, we could not breathe, circulate blood, contract muscles, maintain posture, feel, think, or make cells and tissues. Energy allows us to live.

For humans, energy comes from the food we eat. We need energy for basic functions like breathing, circulating blood, digesting, and maintaining body temperature. We also use energy for moving, thinking, and doing work. The various ways we utilize energy will be explored in more detail throughout this article.


energy provides fuel for all bodily functions
Food provides the energy that humans need to survive and function. The human body runs on energy just like machines and electronics run on electricity. This energy comes in the form of calories from the food and beverages we consume.

When food enters our digestive system, it gets broken down into molecules that can be absorbed and used. The calories we get from carbohydrates, proteins and fats are converted into a form of energy that our cells can utilize. This process happens through metabolism, which is the set of chemical reactions in our bodies that convert food into energy.

The amount of energy we need each day depends on factors like age, sex, body size, and activity level. Someone who is larger or more active will require more calories per day than someone smaller or less active. The recommended daily calorie intake for most adults ranges from 1600-3000 calories per day for women and 2000-3500 for men. This energy is essential for our bodies to perform basic functions like breathing, circulating blood, and replacing cells.


Energy is essential for powering all movement in the human body. The muscles and organs rely on energy to contract and relax, allowing physical activities like walking, running, jumping, and more strenuous exercise. Energy in the form of ATP provides the fuel for muscle contraction.

During exercise and sports, the body requires increased energy expenditure to power the active muscles. Energy usage can increase substantially during intense physical activity as the muscles work harder. Additional energy is needed both for the muscle contractions themselves and to replenish depleted fuel stores like glycogen afterwards. Proper nutrition and energy intake is important for optimal exercise performance and recovery.

Brain Function

The human brain is an incredibly complex and energy-demanding organ. Though it accounts for just 2-3% of total body weight, the brain uses 20% of the body’s energy to power its constant neural activity. This activity enables all of our conscious thought, cognition, learning, and experience of the world around us.

The brain requires a continuous supply of oxygen and glucose from the bloodstream in order to meet its high energy needs. Even brief interruptions in oxygen or glucose can cause mental confusion, loss of consciousness, and even permanent brain damage.

The brain preferentially uses glucose as its primary fuel source. The majority of the brain’s glucose is used to power the ongoing firing of neurons and synaptic transmission between neurons. This synaptic activity is the basis for all of our conscious and subconscious mental activity. The firing of individual neurons also requires significant energy expenditure to maintain the ion gradients essential for generating neural impulses.

In addition to powering moment-to-moment brain function, the brain uses energy to support growth, neurogenesis, and synaptic plasticity – the cellular processes underlying learning and memory. As we learn new information and form new memories, the brain continually adapts and rewires its neural connections, which requires energy.

The high metabolic activity of the human brain underscores its standing as the most complex and energy-demanding organ in the body. Our astonishing cognitive abilities come at a high energetic cost, but allow us to think, reason, learn, and experience the world in a way unmatched by any other species.

Energy for Organ Function

The human body requires a continuous supply of energy to keep its organs functioning properly. Some of the key ways our organs use energy include:


The heart is a muscular organ that pumps blood throughout the body. It beats over 100,000 times per day, pumping about 2,000 gallons of blood. This constant contraction of the heart muscles requires a substantial amount of energy. The heart gets its energy from aerobic respiration, which uses oxygen to convert nutrients into adenosine triphosphate (ATP) – the energy currency of cells.


Breathing is the process by which we inhale oxygen and exhale carbon dioxide. The diaphragm and intercostal muscles power the expansion and contraction of the lungs to move air in and out. Like the heart, these muscles need energy to keep contracting continuously. The process of inhaling and exhaling also requires energy expenditure by other muscles.


Digestion involves breaking down food, absorbing nutrients, and eliminating wastes. Various organs like the stomach, intestines, liver, and pancreas support this process. Contractile movements of smooth muscles in the digestive tract mix food and move it along. Organs also need energy to produce digestive enzymes and acids that act on food. So a regular supply of energy allows our digestive system to keep functioning.

Body Temperature

The human body expends a significant amount of energy to maintain a constant internal temperature of around 98.6°F (37°C). This process is known as thermoregulation. The hypothalamus region of the brain acts as the body’s thermostat, monitoring internal and external temperatures and initiating responses to keep the body within a narrow temperature range.

When the body gets too hot, the hypothalamus triggers sweating to cool the skin through evaporation. Blood vessels also dilate near the skin to radiate heat. If the body gets too cold, the hypothalamus constricts surface blood vessels to minimize heat loss while triggering shivering and muscle contractions to generate more internal heat through metabolism. Chemical hormones like epinephrine can also raise metabolic rate.

These automatic thermoregulation processes require considerable energy expenditure. In fact, around 50-70% of the calories burned at rest go toward maintaining normal body temperature. This energy is vital for cellular function and life itself. Even a change of a few degrees in core temperature can impair enzyme activity and protein structures. Tight regulation of temperature is therefore essential for human energy balance and health.

Energy for the Immune System

The human immune system relies heavily on energy to function properly and fight off illness and infection. White blood cells, antibodies, and other components of the immune system require energy to activate, proliferate, and carry out their defensive duties.

When a pathogen like a virus or bacteria invades the body, the immune system kicks into high gear, ramping up its energy expenditure. Immune cells like T cells and B cells undergo rapid division and proliferation, which demands substantial energy. Cytokines and other signaling molecules are produced to marshal and direct the immune response, another energy-intensive process.

Phagocytes like macrophages and neutrophils engulf and digest pathogens, necessitating energy to power their motors and enzymatic digestion. Inflammation is triggered, which involves increased blood flow and metabolic activity. Fever also raises the body’s temperature setpoint, escalating energy consumption.

All of these immune processes require abundant cellular energy in the form of ATP molecules. Metabolic activity is heightened both locally at sites of infection and systemically throughout the body. This heightened immunometabolism allows immune cells to carry out their critical functions, but it comes at an energy cost.

If the body is energy-depleted due to malnutrition, obesity, or other factors, immune function may be compromised. Ensuring adequate energy intake and reserves is key to maintaining a robust immune system capable of effectively fighting infection.


Reproduction requires a significant amount of energy. The reproductive system in both men and women relies on energy to develop sex cells and hormones that control the reproductive cycle. In women specifically, pregnancy and lactation require large amounts of energy:

– During pregnancy, the body requires extra energy to support fetal growth and development. The recommended calorie intake for pregnant women is around 300 calories more per day than before pregnancy.

– Lactation also has high energy demands, as the body needs energy to produce breastmilk. Breastfeeding mothers require around 400-500 extra calories per day to adequately nourish the baby through breastmilk.

The body pulls from maternal fat stores and increases calorie intake to meet the high energy demands of pregnancy and lactation. Consuming a healthy diet with adequate calories, protein, vitamins and minerals is crucial during this period to support optimal fetal and infant development.


Humans use energy to power a vast array of electronic devices and appliances that make modern life possible. Electricity allows us to light and heat our homes, cook food, wash clothes, access information and communicate across the globe. Without energy, none of our modern electronics would function.

In addition to powering devices inside the home, energy also enables humans to travel using various electronic modes of transportation. Cars, trains, buses, and airplanes all require energy in the form of gasoline, diesel fuel or electricity to function. This allows people to commute to work, travel long distances, transport goods, and engage in recreation through powered vehicles.

Medical devices such as MRIs, CT scanners, pacemakers, ventilators and kidney dialysis machines also rely on electricity to diagnose and treat patients. Hospitals and healthcare facilities are major energy consumers to be able to provide around-the-clock care using complex electronic equipment.

The widespread adoption of personal electronic devices like smartphones, tablets, laptops and wearable tech has increased human energy demand. Even as devices become more energy efficient, the proliferation of electronics results in greater overall energy needs.

In the modern age, electronics empower humans in countless ways. But every use of an electronic device requires energy derived from natural resources like coal, natural gas, nuclear power or renewable sources. Humans harness energy to make their lives easier, more productive and more connected.


Energy is essential for every function of the human body and life itself. As we have explored, energy is used to power basic bodily processes like maintaining body temperature, digesting food, supporting organ function, enabling movement, fueling the immune system and brain, and allowing humans to reproduce. Beyond mere survival, humans also rely on energy to power innovations that improve quality of life – things like transportation, electronics, appliances, and more. While the specific metabolic processes differ, at a fundamental level energy allows humans to live, thrive, and continue advancing as a species.

In summary, energy derived from food is absolutely vital for sustaining human life and society. From enabling a beating heart to powering the technology humanity increasingly depends on, energy is intricately woven into everything humans do. As our understanding of biology and physics grows, so too can our ability to utilize energy in ways that promote health, longevity, and progress.

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