The body requires energy to sustain itself and perform all the functions of daily life. The process of converting nutrients from food into energy is called cellular respiration. The energy from this biochemical process is captured in a chemical called adenosine triphosphate (ATP). Subsequent breakdown of ATP releases the energy needed to drive cellular functions. Carbohydrate, fat and protein provide the fuel needed for energy production from food. Additionally, thiamin, niacin, riboflavin and other B vitamins help with the conversion of nutrients into energy.
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Carbohydrates in the form of sugars, especially glucose, function as the body's preferred fuel for energy production. Glucose is easily and quickly broken down to produce energy. According to an August 2015 article published in "Progress in Molecular Biology and Translational Science," carbohydrates and fat serve as the primary energy sources when the body is at rest. With moderate exercise, carbohydrates provide roughly one-half of the energy needed. During high-intensity exercise, two-thirds of the energy utilized is derived from carbohydrate metabolism. Glucose is stored in the muscles and liver as glycogen, which can be quickly broken down into glucose as energy needs increase. The body can also use other simple sugars from foods, such as fructose and galactose, to generate energy.
Fats and carbohydrates work together to ensure the body has sufficient energy across a variety of circumstances. Gram for gram, dietary fats supply more energy than carbohydrates. Digested dietary fats are processed into triglycerides and free fatty acids, which circulate in the blood and also exist within muscle, liver and fat storage cells, known as adipose tissue. Fatty acids are broken down in several chemical processes to generate ATP. Most of the relatively low level of energy needed when the body is at rest comes from fat metabolism. With moderate-intensity exercise, glucose and fat metabolism contribute roughly equal amounts of energy.
In addition to activity level, other factors influence the balance between carbohydrate and fat metabolism in fueling the body. For example, increased carbohydrate intake triggers a decrease in fat utilization for energy production, as explained in a May 2014 article in "Sports Medicine." In this situation, carbohydrates are preferentially used first and consumed fat is likely to be stored for later use. In contrast, high levels of fatty acids in the blood and muscles tend to decrease the level of use of carbohydrates, particularly at rest and during low-intensity activities.
Dietary proteins are broken down into their constituent amino acids, commonly referred to as protein building blocks. The body primarily uses amino acids to make new proteins, which are used for growth, maintenance and repair of muscles and other body tissues. Amino acids from dietary proteins can be used for energy production, but generally only as a last resort. Some amino acids can be utilized to produce glucose to fuel energy production. Others amino acids can be used in alternate biochemical pathways to generate ATP for energy. During endurance exercise or when the diet contains inadequate carbohydrate and fat, the body will break down muscle and other tissue proteins to release amino acids that can then be used to generate energy.
A February 2016 review article published in "Nutrients" stresses the importance of all B vitamins for the production of ATP. An insufficient supply of any of these vitamins can slow cellular respiration. Thiamin, riboflavin and niacin are the major B vitamins involved in energy metabolism. Thiamin is essential for the conversion of carbohydrates into energy and can be found in foods such as pork, beef, legumes and nuts. Riboflavin participates in several metabolic pathways involved in the generation of energy from carbohydrates, fats and proteins. It occurs in large amounts in foods such as milk, organ meats, eggs, fortified grain products, almonds and yogurt. Niacin also participates in multiple biochemical pathways related to the breakdown and energy conversion of carbohydrates, protein and fats. Rich sources of niacin include chicken, tuna, beef and fortified grain products.
Other B vitamins involved in energy production include pantothenic acid and biotin. Pantothenic acid is a precursor in the body's production of a chemical called coenzyme A, which participates in the biochemical pathways that generate energy from carbohydrates, fats and proteins. Biotin acts with several metabolic enzymes to facilitate the various reactions involved in these energy-generating biochemical pathways.
Warnings and Precautions
Consult with your primary care provider if you experience an unexplained decrease in energy or seek to increase your energy level. Many medical conditions and medications can affect your energy level. Speak with a medical provider before taking any supplements as some can interfere with medications or cause side effects. A referral to a registered dietitian may be necessary to evaluate your diet and determine whether changes are needed.