What are the uses of energy from food?

November 30, 2025 •

3 min read

Approximately 60-75% of your daily energy from food is used for basal metabolic functions, such as breathing and circulation. This critical energy supply is vital for sustaining all life processes, powering everything from your brain activity and physical movement to cellular repair.

Quick Summary

Energy from food powers all bodily functions through cellular respiration. The body uses this energy for essential processes like metabolism, physical activity, growth, tissue repair, and temperature regulation, while storing excess for future use.

Key Points

Metabolic Fuel: Food energy powers basal metabolism, the sum of chemical reactions that keep our cells and organs functioning, even at rest.
Physical Performance: Energy from carbohydrates and fats is converted into ATP to fuel all forms of voluntary muscle movement, from daily activities to intense exercise.
Growth and Repair: A continuous supply of energy is required for tissue growth, cellular repair, and maintenance, especially important during development and recovery from injury.
Temperature Regulation: The body uses energy from metabolism to generate heat and maintain a stable core body temperature, a process known as thermoregulation.
Strategic Storage: Excess energy is stored as glycogen in muscles and the liver for readily available fuel, and as fat for long-term reserves.
Brain Function: The human brain is a major energy consumer, using a significant portion of daily energy intake to function properly.

The food we consume is the fundamental fuel that powers every process within our bodies. Through metabolic reactions, the chemical energy stored within carbohydrates, fats, and proteins is converted into usable energy, measured in calories. This energy is distributed to support a wide range of functions, from basic life-sustaining processes to physical activities. Understanding how our bodies utilize this energy highlights the importance of a balanced diet for overall health.

The Science of Energy: From Food to ATP

Before energy from food can be used, it's converted into adenosine triphosphate (ATP) through cellular respiration, the primary way cells create energy.

Digestion and Nutrient Breakdown

The digestive system breaks down food into smaller units:

Carbohydrates become simple sugars, mainly glucose.
Fats become fatty acids and glycerol.
Proteins become amino acids.

These are absorbed and transported to cells, where energy conversion occurs in the mitochondria.

Cellular Respiration: Producing ATP

In mitochondria, cellular respiration uses oxygen to break down fuel molecules, primarily glucose, producing ATP. Heat is also released, helping maintain body temperature.

Primary Uses of Energy from Food

ATP is used for life-sustaining and voluntary actions.

Basal Metabolic Rate (BMR)

60-75% of daily energy is for involuntary functions, including:

Heart and circulation.
Breathing.
Brain activity (about 20% of total energy).
Maintaining cells.

Physical Activity

All voluntary movement uses energy from food, from walking to strenuous exercise. Carbohydrates fuel high-intensity activity, while fats provide energy for longer durations.

Growth, Repair, and Maintenance

Energy is needed for growth, repair, and tissue maintenance:

Growing new cells, especially during development.
Healing damaged tissues.
Ongoing cell turnover.

Thermoregulation

Energy from food helps maintain stable body temperature. Metabolism generates heat, and energy supports processes to cool down or warm up the body.

Digestion and Nutrient Processing

About 10% of daily calories are used to digest, absorb, and transport nutrients (thermic effect of food - TEF).

Energy Storage for Future Needs

Excess energy is stored for later use.

Glycogen Stores

Glucose is stored as glycogen in the liver and muscles. Liver glycogen maintains blood sugar, while muscle glycogen fuels activity.

Fat Storage

Excess energy is stored as body fat (triglycerides) in adipose tissue. This is the largest, long-term energy reserve.

Comparison Table: Carbohydrates vs. Fats as Energy Sources


Characteristic	Carbohydrates	Fats
Primary function	Immediate energy for high-intensity activity	Long-term, slow-release energy source
Energy density	~4 kcal per gram	~9 kcal per gram
Storage form	Glycogen in liver and muscles	Triglycerides in adipose (fat) tissue
Speed of use	Quick and easily accessible energy	Slower to metabolize for energy
Examples	Bread, rice, pasta, fruit	Oils, nuts, seeds, avocado

Energy Sources for the Body

Fast-acting energy: Simple carbohydrates.
Steady energy: Complex carbohydrates.
Fueling endurance: Fatty acids from fats.
Building blocks and secondary energy: Amino acids from protein.

Conclusion

Energy from food is essential for metabolic functions, physical activity, growth, and repair. Every action is powered by this energy, which is stored as glycogen and fat to ensure a constant supply. A balanced diet with carbohydrates, fats, and proteins is crucial for supporting these processes and maintaining health. For more detailed information, the provided citation offers insights into cellular energy conversion.

Source: The NCBI Bookshelf on How Cells Obtain Energy from Food

Frequently Asked Questions

The body converts food into usable energy through a process called cellular respiration. Digestion breaks down food into simple molecules like glucose, fatty acids, and amino acids. These molecules are then processed in the cells, primarily within the mitochondria, to produce ATP, the cell's energy currency.

The basal metabolic rate (BMR) is the amount of energy the body needs to perform its most basic, life-sustaining functions while at rest. This includes processes such as breathing, blood circulation, and brain function.

The body stores excess energy in two primary ways. First, it converts excess glucose into glycogen, which is stored in the liver and muscles for quick access. Once glycogen stores are full, the body converts the remaining energy into triglycerides and stores them as body fat for long-term use.

Carbohydrates are the body's preferred and fastest energy source, especially for high-intensity activity. Fats provide a more dense, slow-releasing, and long-lasting energy source. Proteins are primarily used for building and repairing tissues but can be used for energy if other fuel sources are depleted.

Yes, eating food can slightly increase body temperature due to the thermic effect of food (TEF), which is the energy required to digest, absorb, and process nutrients. Heat is released as a byproduct of these metabolic reactions.

For physical activity, carbohydrates stored as muscle glycogen provide a quick and accessible source of glucose. For longer, sustained exercise, the body relies more on fat stores for a steady supply of energy.

A balanced diet ensures that the body receives the proper proportions of carbohydrates, fats, and proteins needed for various energy demands. This supports optimal function for both immediate needs and long-term storage, rather than relying on one macronutrient, which can lead to inefficient energy use.