Energy is delivered to the body through the foods we eat and liquids we drink. Foods contain a lot of stored chemical energy; when you eat, your body breaks down these foods into smaller components and absorbs them to use as fuel. Energy comes from the three main nutrients carbohydrates, protein, and fats, with carbohydrates being the most important energy source. In cases where carbohydrates have been depleted, the body can utilise protein and fats for energy. Your metabolism is the chemical reactions in the body’s cells that change this food into energy.
Most of the energy the body needs is for being at rest, known as the Basal Metabolism. This is the minimum amount of energy the body requires to maintain its vital functions such as breathing, circulation and organ functions. The rate at which energy is utilised for such functions is known as the Basal Metabolic Rate (BMR) and varies based on genetics, sex, age, height and weight. Your BMR drops as you get older because muscle mass decreases.
Optimal energy metabolism requires getting sufficient nutrients from our foods, otherwise our energy metabolism underperforms and we feel tired and sluggish. All foods give you energy and some foods in particular help increase your energy levels, such as bananas (excellent source of carbohydrates, potassium and vitamin B6), fatty fish like salmon or tuna (good source of protein, fatty acids and B vitamins), brown rice (source of fibre, vitamins and minerals), and eggs (source of protein). There are actually many foods that provide an abundant amount of energy, particularly those packed with carbohydrates for available energy, fibre or protein for a slow release of energy and essential vitamins, minerals and antioxidants.
Foods are metabolised at a cellular level to make ATP (Adenosine Triphosphate)
by a process known as cellular respiration. It is this chemical ATP that the cell uses for energy for many cellular processes including muscle contraction and cell division. This process requires oxygen and is called aerobic respiration.
Glucose + Oxygen → Carbon dioxide + Water + Energy (as ATP)
Initially, large food macromolecules are broken down by enzymes into simple subunits in the process known as digestion. Proteins are broken down into amino acids, polysaccharides into sugars, and fats into fatty acids and glycerol—through the action of specific enzymes. Following this process, the smaller subunit molecules then have to enter the cells of the body. They firstly enter the cytosol (the aqueous part of the cytoplasm of a cell) where the cellular respiration process begins.
There are four stages of aerobic cellular respiration that occur to produce ATP (the energy cells need to do their work):
Stage 1 Glycolysis (also known as the breakdown of glucose)
This occurs in the cytoplasm and involves a series of chain reactions known as glycolysis to convert each molecule of glucose (a six-carbon molecule) into two smaller units of pyruvate (a three-carbon molecule). During the formation of pyruvate, two types of activated carrier molecules (small diffusible molecules in cells that contain energy rich covalent bonds) are produced, these are ATP and NADH (reduced nicotinamide adenine dinucleotide).This stage produces 4 molecules of ATP and 2 molecules of NADH from glucose but uses 2 molecules of ATP to get there,- so it actually results in 2 ATP + 2 NADH and pyruvate. The pyruvate then passes into the mitochondria.
Stage 2 The Link reaction
This links glycolysis with stage 3 the Citric acid/ Krebs cycle, which is explained below. At this point, one carbon dioxide molecule and one hydrogen molecule are removed from the pyruvate (called oxidative decarboxylation) to produce an acetyl group, which joins to an enzyme called CoA (Coenzyme A) to form acetyl-CoA, which is then ready to be used in the Citric acid/Krebs cycle. Acetyl-CoA is essential for the next stage.
Stage 3 The Citric Acid/Krebs Cycle
Taking place in the mitochondria, the acetyl-CoA (which is a two-carbon molecule) combines with oxaloacetate (a four-carbon molecule) to form citrate (a six-carbon molecule). The citrate molecule is then gradually oxidized, allowing the energy of this oxidation to be used to produce energy-rich activated carrier molecules. The chain of eight reactions forms a cycle because, at the end, the oxaloacetate is regenerated and can enter a new turn of the cycle. The cycle provides precursors including certain amino acids as well as the reducing agent NADH that are used in numerous biochemical reactions.
Each turn of the cycle produces two molecules of carbon dioxide, three molecules of NADH, one molecule of GTP (guanosine triphosphate) and one molecule of FADH2 (reduced flavin adenine dinucleotide).
Because two acetyl-CoA molecules are produced from each glucose molecule utilised, two cycles are required per glucose molecule.
Stage 4 Electron Transport Chain
In this final stage, the electron carriers NADH and FADH2, which gained electrons when they were oxidizing other molecules, transfer these electrons to the electron transport chain. This is found in the inner membrane of the mitochondria. This process requires oxygen and involves moving these electrons through a series of electron transporters that undergo redox reactions (reactions where both oxidation and reduction take place). This causes hydrogen ions to accumulate in the intermembrane space.
A concentration gradient then forms where hydrogen ions diffuse out of this space by passing through ATP synthase. The current of hydrogen ions powers the catalytic conversion of ATP synthase, which, in turn, phosphorylates ADP (adds a phosphate group) therefore producing ATP. The endpoint of the chain occurs when the electrons reduce molecular oxygen, which results in the production of water.
Although there is a theoretical yield of 38 ATP from the breakdown of one glucose molecule, realistically it is thought 30-32 ATP molecules are actually generated.
This process of aerobic respiration takes place when the body requires sufficient energy just to live, as well as to carry out everyday activities and perform cardio exercise. While this process yields more energy than the anaerobic systems, it is also less efficient and can only be used during lower-intensity activities.
So, if you have SLOW and STEADY energy requirements, your NET ENERGY PRODUCTION from aerobic respiration equals 30-32 Molecules of ATP.
Glucose + Oxygen → Carbon dioxide + Water + Energy (as 30-32 ATP)
The body releases carbon dioxide and water in this process. This will theoretically burn the highest number of calories.
Under other physiological conditions the body can still acquire its energy in other ways:
There are further energy processes the body uses to create ATP, they depend on the speed at which the energy is required and whether they have access to oxygen or not.
Human muscle can respire anaerobically, a process that does not require oxygen. The process is relatively inefficient as it has a net energy production of 2 molecules of ATP.
This is effective for vigorous exercise of between 1-3 minutes duration, such as short sprints. If the intense exercise requires more energy than can be supplied by the oxygen available, your body will partially burn glucose without oxygen (anaerobic). Without the presence of oxygen, the electron transport chain cannot work. Therefore, the usual number of ATP molecules cannot be made. The anaerobic pathway uses pyruvate, the final product from the glycolysis stage. Pyruvate is reduced to lactic acid by NADH, leaving NAD+ after the reduction. This reaction is catalysed by an enzyme (lactate dehydrogenase) and leads to the recycling of NAD+. This then allows the process of glycolysis to continue.
This glycolysis pathway yields 2 molecules ATP, which can be used for energy to drive muscle contraction. Anaerobic glycolysis occurs faster than aerobic respiration as less energy is produced for every glucose molecule broken down, so more has to be broken down at a faster rate to meet demands.
Lactic acid (the by-product from anaerobic respiration) builds up in the muscles causing the “burn” felt during strenuous activity. If more than a few minutes of this activity are used to generate ATP, lactic acid acidity increases, causing painful cramps. The extra oxygen you breath in following intensive exercise, reacts with the lactic acid in your muscles, breaking it down to make carbon dioxide and water.
So, summing up: Exercises that are performed at maximum rates for between 1 and 3 minutes depend heavily on anaerobic respiration for ATP energy. Also, in some performances, such as running 1500 meters or a mile, the lactic acid system is used predominately for the “kick” at the end of a race.
Therefore, if you are doing VIGOUROUS EXERCISE for 1-3 minutes, there will be NO TISSUE OXYGEN AVAILABLE so you will see a NET ENERGY PRODUCTION from anaerobic respiration equal to 2 molecules of ATP.
Beta Oxidation/Gluconeogenesis or Fat Burning (Aerobic Lipolysis)
A fat molecule consists of a glycerol backbone and three fatty acid tails. They are called triglycerides. In the body, they are stored primarily in fat cells called adipocytes making up the adipose tissue. To obtain energy from fat, the triglyceride molecules are broken down into fatty acids in a process called ‘Lipolysis’ occurring in the cytoplasm. These fatty acids are oxidized into acetyl- CoA, which is used in the Citric acid/Krebs cycle. Because one triglyceride molecule yields three fatty acid molecules with 16 or more carbons in each one, fat molecules yield more energy than carbohydrates and are an important source of energy for the human body (over 100 molecules of ATP generated per molecule of fatty acid). Therefore, when glucose levels are low, triglycerides can be converted into acetyl-CoA molecules and used to generate ATP through aerobic respiration.
This need arises after any period of not eating; even with a normal overnight fast, mobilization of fat occurs, so that by the morning most of the acetyl-CoA entering the Citric acid/Krebs cycle comes from fatty acids rather than from glucose. Following a meal, however, most of the acetyl-CoA entering the Citric acid/Krebs cycle comes from glucose from food, with any excess glucose being used to replenish depleted glycogen stores or to synthesize fats.
This is a SLOW, NOT IMMEDIATE ENERGY SOURCE but has a NET ENERGY PRODUCTION of over 100 molecules of ATP.
ATP Phosphocreatine (ATP-PC)
This energy system consists of ATP (all muscle cells have a little ATP in them) and phosphocreatine (PC), which provide immediate energy from the breakdown of these high energy substrates.
Firstly, ATP that is stored in the myosin cross-bridges (within the muscle) gets broken down producing adenosine diphosphate (ADP) and one single phosphate molecule. Then, an enzyme, known as creatine kinase, breaks down phosphocreatine (PC) to creatine and a phosphate molecule. This breakdown of phosphocreatine (PC) releases energy, which allows the adenosine diphosphate (ADP) and phosphate molecule to re-join forming more ATP. This newly formed ATP can then be broken down to release energy to fuel activity. This will continue until creatine phosphate stores are depleted.
Short, sharp explosive bursts of exercise (10-30 secs) use this system. It doesn’t require oxygen but is very limited to short periods of explosive exercise, such as a sprint or weight/power lifting. This is why creatine supplementation helps this sort of exercise, ensuring there is adequate creatine phosphate to provide those required phosphates. The ATP-CP system usually recovers 100% in 3 mins; so, the recommended rest time in between high intensity training is 3 minutes.
In short, for sharp explosive bursts of exercise needing FAST, IMMEDIATE energy this system produces COPIUS AMOUNTS OF ATP until the creatine phosphate in muscles runs out.
Different forms of exercise use different systems to produce ATP
Role of gut bacteria in energy regulation
Gut bacteria plays an important role in nutrient and energy extraction and energy regulation. The bacteria makes a multitude of small molecules (known as metabolites) that can act as signals that can modulate appetite, energy uptake, storage and expenditure, something which is explored in the review article Gut Microbiota-Dependent Modulation of Energy Metabolism.
Gut bacteria influences the bioavailability of polysaccharides and how this occurs is unclear but it is an increasing area of research, with this 2016 paper, on the causality of small and large intestinal microbiota in weight regulation and insulin resistance, investigating the subject at length.
Side effects with low energy levels
Not properly managing your energy levels can result in both physical and cognitive functions being affected.
Physical signs can include: reduced stamina, reduced strength and less ability to recover from exercise.
Performance related effects can include: loss of focus, slow reaction times, low mood, poor working memory, poor decision making and decreased reaction times.
Food Supplements to support your energy processes
Whilst there are many ways to maintain your energy, such as consuming a balanced diet, getting sufficient sleep and exercising regularly, these things are not always possible for some people. In times like these, food supplements may help support your overall energy requirements
Acetyl Coenzyme A (Acetyl-CoA) is an important molecule in metabolism. It delivers the acetyl group to the Citric acid/ Krebs cycle, releasing ATP (energy) and forming carbon dioxide and water. It is important to have enough acetyl-CoA to feed into the citric acid cycle to provide energy.
Alpha-lipoic acid (ALA), also known as lipoic acid or thioctic acid, acts as an antioxidant and is naturally present in the mitochondria. Alpha lipoic acid serves as a cofactor for enzymes that participate in cell metabolism that produce ATP. It acts as an antioxidant by scavenging free radicals. Whilst the body can make sufficient ALA for basic energy metabolism it only acts as an antioxidant when it’s there in larger amounts as discussed in this paper on Alpha-lipoic acid as a dietary supplement.
Arginine is involved in many metabolic processes, as explored in this paper Novel metabolic roles of L-arginine in body energy metabolism and possible clinical applications. These processes include protein metabolism and creatine synthesis. Arginine is also the precursor of nitric oxide (NO), an important neurotransmitter and vasodilator. It is reported that supplementation with L Arginine may increase ATP regeneration via activation of AMP Kinase pathway.
Ashwagandha, whilst not classed as an energy booster, can have an effect on physical and mental performance. It is used as a general tonic (to help maintain optimal stamina, feelings of energy and vitality), adaptogen and an antioxidant. Adaptogens are non-toxic plants that help support the body resist stress, whether it be physical, chemical or biological. Ashwagandha also helps maintain mental balance and supports learning, memory and recall. Ashwagandha may help lower cortisol levels (the hormone released in stressful situations) in chronically stressed individuals, according to this paper on the study of ashwagandha root in reducing stress and anxiety in adults.
B Complex liquid or B Complex capsules includes a blend of all the B vitamins, which are water soluble and have roles in supporting your normal energy yielding processes. You can read more about our B Complex product in our Vitamin B Complex article.
Carnitine has an important role in energy metabolism by transferring long chain fatty acids into the mitochondria for beta-oxidation. It also aids with the removal of acetyl Coenzyme A metabolites by binding to them for excretion in the urine. Carnitine is the generic term for a number of compounds that include L-carnitine and acetyl-L-carnitine. Animal products like meat, fish, poultry are the best sources of carnitine. A decline in mitochondrial function is thought to contribute to the aging process. This research paper on carnitine , found that supplementing with high doses of acetyl-L-carnitine and alpha-lipoic acid reduced mitochondrial decay.
Coenzyme Q10 (CoQ10) transfers electrons in the electron transport chain as part of ATP production. In its reduced form, it is a powerful antioxidant. It is particularly important in cells that have high-energy requirements such as those of the heart that are particularly sensitive to CoQ10 deficiency. As CoQ10 is lipid or fat soluble, it is advisable to take this product with a meal containing fat. It is found in many foods such as heart, liver, kidney, spinach, cauliflower and broccoli etc. CoQ10 declines with age and when levels of CoQ10 decline, as shown in this 2014 research on CoQ10, your cells cannot produce the energy they need and this can result in fatigue.
Iodine. The thyroid gland traps iodine from the blood as it is needed to form thyroxine (T4) and Triiodothyronine (T3). These are thyroid hormones and are essential for normal thyroid function. Thyroid hormones help the body make energy. When levels of thyroid hormones are low, the body can’t make as much energy as it usually does. Deficiency of iodine can therefore result in fatigue and weakness. Good food sources of Iodine are shellfish and sea fish as well as in the plant-based foods such as cereals and grains.
Iron is an essential mineral that contributes to normal energy-yielding metabolism. The body needs iron to make haemoglobin, which is the protein in red blood cells that transports oxygen throughout your body. Iron deficiency (anaemia) can leave you feeling fatigued and weak. Vitamin C is included in the Metabolics Iron and Vitamin C formulation as it increases the bioavailability of iron.
Magnesium has a predominant role in the production and use of ATP, as it forms Mg-ATP complexes. These complexes are cofactors for several kinases that are active during glycolysis. Magnesium also regulates the activity of several enzymes involved in the Citric acid/Krebs cycle. You can read more about magnesium and its functions in the Practitioner’s Guide to Magnesium.
Niacin, also known as Vitamin B3 is a precursor of the coenzymes nicotinamide adenine dinucleotide (NAD) and NAD phosphate (NADP), which are involved in many metabolic reactions. NAD and its reduced form NADH play an important role in energy metabolism by transferring electrons in the mitochondrial electron transport chain. Niacin also has antioxidant properties and prevents oxidative stress. Foods high in niacin include liver, chicken, tuna, salmon, avocado, brown rice and peanuts.
Riboflavin, also known as vitamin B2 is a component of the flavoproteins flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN). These act as electron carriers in the mitochondrial electron transport chain and are involved in fatty acid oxidation and the Citric acid/Krebs cycle therefore contribute to normal energy yielding metabolism. Riboflavin is found naturally in eggs, lean meats, green vegetables and fortified cereals.
Ribose is an important sugar that is an important component of the nucleotide RNA. It is an energy source made from food and is the fuel for mitochondria to produce ATP which provides cellular energy. Some research, which looks at the effect of ribose supplementation on resynthesis of adenine nucleotides after intense intermittent training suggests D-Ribose supplements may help recover stores of ATP in muscle cells. Typical foods containing ribose include mushrooms, cheese, milk, and eggs.
Thiamine, also known as Vitamin B1 contributes to your normal energy yielding metabolism. Thiamine Hydrochloride is the salt form of thiamine, essential for aerobic metabolism, cell growth, transmission of nerve impulses and acetylcholine synthesis. When it is hydrolysed, thiamine hydrochloride is phosphorylated to the active form thiamine pyrophosphate. This is a coenzyme for many enzymatic activities involving fatty acid, amino acid and carbohydrate metabolism. When glucose is broken down into energy, thiamine is a cofactor in the process of converting pyruvate to acetyl coenzyme A. Pyruvate is critical for numerous aspects of human metabolism, something that is explored in this research on the regulation of pyruvate metabolism and human disease. Thiamine is found naturally in many foods including whole grains, pasta, rice, pork, fish, legumes, seeds and nuts.
Vitamin C, also known as L-Ascorbic acid contributes to normal energy-yielding metabolism. It acts as an antioxidant that has the ability to regenerate other antioxidants. Vitamin C also facilitates the intestinal absorption of nonheme iron, as is detailed in this research on vitamin C function. People are unable to synthesize vitamin C endogenously, so it is an essential dietary component. Foods rich in vitamin C include broccoli, cantaloupe, cauliflower, kale, kiwi, orange juice, papaya, red, green or yellow pepper, sweet potato, strawberries, and tomatoes.
Vitamin E is a fat soluble compound with antioxidant activities, helping protect cells from the damage caused by free radicals. Free radicals are compounds formed when our bodies convert the food we eat into energy. Naturally occurring vitamin E has eight chemical forms, known as vitamin E tocotrienols, (alpha-, beta-, gamma-, and delta-tocopherol and alpha-, beta-, gamma, and delta-tocotrienol). Nuts, seeds, and some oils tend to contain the most vitamin E per serving.
Vitamin K is a fat soluble cofactor for enzymes involved in blood clotting and bone metabolism. It acts as an antioxidant and can donate electrons. There are two forms, K1 and K2, distinguishable by two main structures phylloquinone (K1) and menaquinones (K2). A 2019 review on the differences between K1 and K2 suggests that the body can absorb up to ten times more vitamin K2, as MK7, than vitamin K1. Vitamin K2, is only found in animal sourced foods and fermented plant foods, such as natto.
Metabolics offers a range of food supplements to support your nutritional needs and energy requirements. Whilst the best way to do this is through a well-balanced diet, exercise, reduce your exposure to stress and ensure you get plenty of sleep, our supplements are there to provide high quality ingredients to support you along the way.
If pregnant, breast feeding or taking medication it is advised that you consult with a health care practitioner before using these products.