Energy is one of the primary markers of health. Often, when people are asked about their health, low energy is a common complaint. Likewise, when people identify a benefit from a nutritional supplement, “improved energy” is the first they’ll report. What many people don’t realize, however, is that energy and amino acids go hand in hand.
Most everyone, even the most energetic among us, desires more energy. It is no accident that “energy” drinks have become so popular. However, the concept of energy is somewhat vague. What does having energy really mean?
To understand the relationship between energy and amino acids, we must first distinguish between physical and mental energy. These two types of energy are clearly related, but distinct. By considering physical and mental energy separately we can better understand the physiological basis for each.
Energy and Amino Acids: What Fuels Our Bodies?
Physical energy requires not just fuel for our bodies, but all of the necessary vitamins and cofactors required to convert food to an energy form that our cells can utilize.
Assuming that all vitamins and cofactors are available, the energy necessary for all physiological functions is derived from the oxidation of carbohydrates, fat, protein, and (in some cases), alcohol. These energy substrates can be considered the “fuel” of the body.
The major form of chemical energy in the body is a compound called adenosine triphosphate (ATP). Energy is released when ATP is broken down to adenosine diphosphate (ADP) and phosphate. ATP is regenerated by the metabolism of the macronutrient energy substrates listed above, as well as by the oxidation of amino acids.
Chemical Energy and Mitochondria
The energy needed to perform physical functions such as exercise comes from the chemical energy stored in ATP. ATP is the universal fuel used by all cells.
In general, food is digested and absorbed as its basic components (glucose and other simple sugars, fatty acids, and amino acids), which are then used for structural needs, stored away, or oxidized for energy.
The oxidation of nutrients into chemical energy involves complex biochemical pathways. The Krebs Cycle, named after its discoverer (and also known as the tricarboxylic acid (TCA) cycle) involves a series of chemical reactions in which carbon structures derived from carbohydrate, fat, and protein are metabolized, with the production of ATP as a byproduct. The TCA cycle operates inside mitochondria, which are specialized organelles within the cells.
Oxidation of Amino Acids for ATP Production
The majority of physical energy comes from the oxidation of fats and carbohydrates. However, every amino acid in the body can also potentially be oxidized to produce ATP. The amount of oxidation of the essential amino acids (EAAs—the nine dietary amino acids that can’t be produced in the body) determines how much of an individual essential amino acid you need in a day.
Body protein will be lost if a steady supply of all EAAs is not maintained. Therefore, any EAA that is oxidized must be replaced through the diet. The oxidation of EAAs is thus important physiologically, even though only a minimal amount of total energy production is derived from their oxidation. At rest, less than 10% of energy production comes from the oxidation of amino acids.
Exercise greatly increases the requirements for ATP, and part of that ATP comes from amino acid oxidation. However, the oxidation of all amino acids is not increased uniformly during exercise. Among the EAAs, there is a selective increase in the oxidation of leucine. Even with the increase during exercise, however, leucine oxidation only provides about 3-4% of energy for ATP production. However, leucine plays a crucial regulatory role for protein synthesis and other metabolic processes, so extra leucine needs to be consumed after exercise in order to replace what was oxidized.
While amino acids, particularly EAAs, do not play much of a role in overall energy production, there are a number of aspects of amino acid oxidation that are important in the metabolic regulation of the body. To understand the critical nature of EAA oxidation is to appreciate that the body regulates the availability of all EAAs at a relatively constant level. Consuming a high-protein meal causes EAA availability to increase. The increased concentrations of EAAs stimulate their oxidation in order to minimize changes in EAA availability. Conversely, if you do not consume enough EAAs through your diet, metabolic adaptations occur that reduce the rate of EAA oxidation.
The oxidation of specific amino acids is important for the body. For example, the availability of certain amino acids depends on the oxidation of other amino acids. Take tyrosine, for example. This amino acid is produced in the liver from the oxidation of the EAA phenylalanine. Maintaining an adequate amount of tyrosine in the blood is crucial because tyrosine is a precursor for the neurotransmitters dopamine, norepinephrine, and epinephrine.
Also, specific tissues and organs have metabolic preferences for certain amino acids. Most prominently, glutamine (a nonessential amino acid), is a preferred substrate for the gut.
Amino Acids Augment Mitochondria
Only recently have we begun to appreciate that the number of mitochondria available and their ability to operate at full capacity can make a discernible difference in our energy levels. Both amino acid supplementation and exercise are known to increase mitochondrial number and enhance function.
In contrast, alcohol and drug use has been shown to induce mitochondrial defects by increasing oxidative stress and damaging mitochondrial genetic material (deoxynucleic acid, DNA). When ethanol damages mitochondrial DNA, it impairs mitochondrial function, which further increases oxidative stress in the cell, leading to a vicious cycle of accumulating cell damage and decreased energy production over time.
Mental Energy: What Balances Our Brains?
Energy drinks typically contain caffeine and perhaps some B vitamins. These beverages clearly wake you up, sharpen concentration, and increase the feeling of energy.
Surprisingly, amino acids play just as much of an important role as caffeine does in maintaining mental energy and focus. Amino acids impact mental energy by modulating neurotransmitters within the brain.
Many of the neurotransmitters in the brain are produced from amino acids. The interaction of the neurotransmitters in the brain determines many aspects of behavior. To simplify a very complex system, the key determinant of mental energy is the balance between the brain neurotransmitters dopamine (excitatory) and serotonin (inhibitory).
The amounts of dopamine and serotonin in the brain are dependent on the availability of the precursors for their production. Tyrosine is the amino acid precursor of dopamine, and tryptophan is the amino acid precursor for the production of serotonin. Tyrosine is derived from the oxidation of phenylalanine. Neither phenylalanine nor tryptophan is made in the body (they are both EAAs). Increasing the amount of phenylalanine consumption will, via conversion to tyrosine, increase mental energy by increasing the amount of dopamine. Conversely, tryptophan will induce the feeling of sleepiness or lack of energy by promoting serotonin production.
Amino Acid Balance and Mental and Physical Energy
There are a range of roles played by specific amino acids in supporting both physical and mental energy. While supplementation with individual amino acids may support particular reactions, disrupting the balance of amino acids by consuming a single or small combination of amino acids may be counterproductive with regard to other functions.
An amino acid supplement containing relatively high phenylalanine (tyrosine is nearly insoluble and difficult to add to a nutritional supplement) and low tryptophan can provide mental sharpness and focus. However, an isolated increase in phenylalanine can induce Parkinson’s-like symptoms in susceptible individuals.
Consumption of leucine can counter the accelerated rate of oxidation during exercise, but consumption of only leucine will activate the oxidation of valine and isoleucine, thereby limiting muscle protein synthesis. Consequently, to replace the oxidized leucine it is necessary to provide all three of the branched-chain amino acids (leucine, isoleucine, and valine).
Finally, all the EAAs must be elevated to stimulate muscle protein synthesis, which is the metabolic basis for increased strength and function. Consequently, the most efficacious approach to maintaining both mental and physical energy is to consume a formulation of EAAs that accounts not only for the direct actions of the component amino acids, but also the importance of maintaining a relative balance of EAA availability to sustain maximal benefit.