Your body is an energy-burning machine. About one-third of your energy is spent on voluntary activities, such as cleaning the house or going on a walk. The other two-thirds is consumed by involuntary functions you’re not aware of, like maintaining your heartbeat, fighting off an infection, and breathing.1  

To meet this demand, your body processes and breaks down nutrients and either uses them instantly for fuel or stores them for later use. This efficient natural storage system ensures you have a readily available source of energy to perform any duty or function.1 

Striking the right balance of stored energy is key to maintaining a healthy weight and providing the fuel your body needs. Here’s what you need to know.

Energy: It’s what the body needs 

Your body requires a substantial supply of energy to power the essential functions it performs. The minimal amount of energy required to fuel your body’s biological processes is called basal metabolic rate (BMR) or baseline metabolism. And BMR plays a more significant part in energy consumption than you might realize.1 

For example, your heart consumes 9 percent of your BMR just to keep beating. The complexity of your brain and its electrical network consumes another 20 percent of your resting energy.1

Your immune system is also demanding. For a sedentary individual who is 5 feet 9 inches tall and weighs 187 pounds, the immune system consumes more than a quarter of that person’s BMR during a mild immune response.2 

Activities like going for a walk, cleaning the garage, or pushing through a tough workout require your body to produce even more energy. To fuel your “extra” activities and maintain a steady supply for fundamental functions, the human body has developed ingenious ways to store energy and call on it when needed. 

Energy storage: Saving for a demanding day

In the early days of evolution, humans faced alternating periods of feast or famine. They spent long days foraging for food. Some days, their efforts were successful, and food was plentiful. Other times, there was little in the way of nourishment. To survive and cope with an inconsistent supply of food, humans (and other animals) developed what is called metabolic flexibility – the body’s ability to use various fuel sources for energy.2,3 

Humans derive energy by consuming carbohydrates, fats, and proteins. Carbohydrates are the body's primary source of fuel. The body breaks down carbohydrates into a type of sugar called glucose. After eating, as soon as glucose enters the bloodstream, the body can use it as energy.1 

The body stores unused glucose as glycogen, primarily in the liver and muscles, to use when food is scarce or to meet an increased demand for energy. For example, during exercise, cells use glucose that is circulating in the blood, stored glycogen, or fatty acids to create energy. If an exercise session is especially long and glycogen levels drop, then the body shifts to using fatty acids to fulfill more of its energy needs. However, the body still requires some glucose to utilize fats for energy, so if glycogen is depleted, then exercising becomes challenging.4,5 

Sometimes fatty acids aren’t enough to meet the body’s energy needs, particularly in a fasting state. When this happens, the liver steps in and creates molecules from fatty acids and turns them into ketones, a chemical that the brain, heart, and other muscles use as an alternative fuel source.1

The ability to switch to alternative energy sources is particularly important for the brain, which uses about 60 percent of the glucose circulating in the bloodstream when the body is at rest. To always ensure a stable supply of glucose, the liver uses its glycogen stores to release glucose into the bloodstream as needed.4

Stored energy: When too much becomes a bad thing

Today, the human body is still programmed to think “feast or famine” when deciding how to use fuel. But unlike the food scarcity issues that faced our ancestors, overeating and a sedentary lifestyle plague many individuals in modern society.3 

As a result, excess energy isn’t always burned, and an overabundance of food fails to trigger a shift between fuel sources. So, the body ends up with more fat in storage than it can use.3

The body uses a process called lipogenesis to convert excess energy into a type of fat called triglycerides, stored mainly in adipose (fat) tissue. Adipose tissue is a crucial energy-storage site. But when faced with too much energy to hold, adipose tissue adapts by increasing the size of fat cells (hypertrophy) and number of fat cells (hyperplasia), which can impair normal cellular functions. Research links increased adipose tissue and these adverse cellular changes to conditions such as insulin resistance, type 2 diabetes, obesity, heart disease, and some forms of cancer.3,6

Fuel: Keep just the right amount in your tank

The solution to a balanced energy supply lies in the tried-and-true: The right exercise and diet regimen. In general, move your body for a minimum of 30 minutes of moderately vigorous exercise at least five days a week.1,7 Not sure what your nutritional or caloric requirements are? Then consult with a registered dietitian or health-care professional to determine the right balance for maintaining a healthy weight and energy level. 

You also can use an online calculator that determines your caloric needs based on your age, sex, height, weight, and level of physical activity. The Dietary Guidelines for Americans offers a free online calculator that determines what and how much to eat within your calorie allowance. You can access it here: The MyPlate Plan.

By understanding how your body stores and uses energy, you can pay better attention to its energy needs and ensure your body has the right amount of fuel to operate smoothly and efficiently. Striking this balance helps maintain a healthy weight and an active life. 

A word from Thorne

The complex cellular processes that regulate energy require a number of vitamin and minerals co-factors for optimal function, yet a modern diet can lead to less-than-optimal intake of many of these micronutrients. Consider a multi-vitamin/mineral, like Basic Nutrients 2/Day, to help meet nutritional gaps and maintain energy in your tank.

References

  1. Bender DA, Cunningham SMC. Introduction to Nutrition and Metabolism. 6th ed. CRC Press; 2021. 
  2. Straub RH. The brain and immune system prompt energy shortage in chronic inflammation and ageing. Nat Rev Rheumatol. 2017;13(12):743-751.
  3. Palmer BF, Clegg DJ. Metabolic flexibility and its impact on health outcomes. Mayo Clin Proc. 2022;97(4):761-776.
  4. Murray B, Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev. 2018;76(4):243-259.
  5. How nutrients impact physical performance. Mayo Clinic. https://www.mayoclinichealthsystem.org/hometown-health/speaking-of-health/how-nutrients-impact-physical-performance. [Accessed February 10, 2024]
  6. Stenkula KG, Erlanson-Albertsson C. Adipose cell size: Importance in health and disease. Am J Physiol Regul Integr Comp Physiol. 2018;315(2):R284-R295.
  7. Physical Activity Guidelines for Americans. 2nd Edition. U.S. Department of Health and Human Services. https://health.gov/our-work/nutrition-physical-activity/physical-activity-guidelines/current-guidelines. [Accessed February 20, 2024]