Fatigue is generally defined as extreme tiredness due to exertion or illness, whereas energy refers to the actual or perceived ability to power physical and mental activity. Fatigue in exercise science is slightly different: fatigue is characterized as diminished output in response to sustained effort.^[1] The broad topic of fatigue and energy is related to nutrient status, metabolism and energetics (i.e. mitochondria function), exercise, physiology, psychology, neurobiology, oxidative stress, inflammation, sleep, and many body systems. Fatigue can be as mild as feeling tired regularly, or as extreme as the disabling fatigue indicative of a severe medical condition (i.e. chronic fatigue syndrome (CFS), also known as ME/CFS).^[2]

Food choice is foundational for sustaining energy, as calories are metabolized into ATP, the primary source of energy that fuels cell needs. Healthy, nutrient dense dietary patterns support the energetic demands of life, prevent conditions that increase risk for fatigue, and have been used in studies to reduce fatigue and increase energy.^[3][4] Some foods contain nutrients at doses shown to support energy and resist fatigue either in general (e.g., iron in red meat) or during exercise (e.g., nitrates in spinach).^[5]

Getting enough essential vitamins and minerals (e.g., iron for blood cell function, B-complex vitamins for metabolism support) is foundational in any approach designed to address fatigue, which means that supplementation can be beneficial if the diet does not provide enough of these nutrients.

The most common supplements used for increasing mental and physical energy are stimulants (e.g., caffeine, guarana). Supplements that improve cognitive function, like nootropics, are also related to increasing energy.

Supplements that increase endurance, support fatigue resistance, promote stress tolerance, or have another effect on enhancing exercise (such as ergogenics) are relevant to energy and fatigue.