Biochemistry
bio·chem·is·try
\ˌbī-ō-ˈke-mə-strē\
noun
1. Chemistry that deals with the chemical compounds and processes occurring in organisms.
Biochemistry is the combination of biology and chemistry that focuses on the chemical processes that occur in living organisms. While it is not a pillar of health in and of itself, it explains the underlying mechanisms behind each pillar and how they contribute to our health at the chemical level. Biochemistry deals with components of nutrition like carbohydrates, fats, and proteins, while further explaining how we metabolize these components into nutrients that our bodies can use. Biochemistry also deals with components of fitness like how we use the energy in our bodies to produce movement, while further explaining how our bodies build muscle after strength training. Since biochemistry is the science of life, it is the most important area to understand to build deeper knowledge on how to optimize each pillar, to improve our overall health.
One component in the biochemistry of health is energy balance, which focuses on the "calories in, calories out" (CICO) model. This equation states that if we constantly consume less calories than we are expending, we create a caloric deficit and lose body fat in proportion to the amount of calories below our maintenance energy balance (Howell & Kones, 2017). For example, if our daily maintenance energy balance is 2,500 calories, and we consume 2,000 calories a day for a week, we should lose about 1 pound of body fat by the end of that week, assuming that calories remain the only thing changed and that 3,500 unconsumed calories is typically equivalent to 1 pound of body fat. In contrasts, if we constantly consume more calories than we are expending, we create a caloric surplus and gain body fat in proportion to the amount of calories above our maintenance energy balance. For example, if our daily maintenance energy balance is 2,500 calories, and we consume 3,000 calories a day for a week, we should gain about 1 pound of body fat by the end of that week, assuming that calories remain the only thing changed and that 3,500 additional calories is typically equivalent to 1 pound of body fat. We remain at our maintenance energy balance by constantly consuming the same amount of calories we expend. For example, if our daily maintenance energy balance is 2,500 calories, and we consume 2,500 calories a day for a week, we should not gain or lose body fat by the end of that week, assuming that all other factors remain unchanged as well. The CICO model is supported by the evidence that a calorie is a measure of the energy in food, and that our body uses this energy for all of our daily processes and activities. Therefore, extra energy (calories) is stored as body fat which can be utilized for future metabolism whenever energy consumption is lower than energy expenditure. We mostly gain weight whenever that extra energy is stored as body fat and we mostly lose weight whenever that extra energy stored as body fat is metabolized, released into the bloodstream, and utilized by our cells.
The glycemic index is a component in the biochemistry of health which focuses on carbohydrates and the glucose they release. The glycemic index is a measure of how slowly or quickly each food (carbohydrates) raises the levels of glucose in the bloodstream (Harvard Health Publishing, 2020). The index assigns each food a value from 0-100 with low glycemic foods being carbohydrates 55 and under, medium glycemic foods being carbohydrates between 56-69, and high glycemic foods being carbohydrates 70 and above. Carbohydrates higher on the glycemic index are broken down quicker and glucose is released into the bloodstream quicker, than carbohydrates lower on the glycemic index. When glucose is released into the bloodstream, insulin is released by the pancreas to regulate blood sugar levels and carry glucose to the cells. When glucose is released slowly into the bloodstream by low glycemic foods, the pancreas releases moderate amounts of insulin to bring down slightly elevated blood sugar levels, to prevent them from elevating too high. However, when glucose is released quickly into the bloodstream by high glycemic foods, the pancreas releases excessive amounts of insulin to bring down extremely elevated blood sugar levels, and the glucose ends up mostly being absorbed by fat cells. Refined carbohydrates that are high in sugar tend to be high glycemic as they are broken down quicker and release glucose into the bloodstream quicker, causing spikes in blood sugar levels. Fruits and vegetables tend to be low glycemic foods as they contain dietary fiber which slows the rate that they are broken down and released into the bloodstream, causing blood sugar levels to elevate slightly before being brought back down to moderate levels. This is why it is important for our diet to consists of mostly whole foods rather than processed foods, so our blood sugar levels can be managed efficiently and we can reduce the risk of chronic diseases related to obesity such as diabetes.
Another component in the biochemistry of health that is part of the "calories in, calories out" (CICO) energy balance model, is energy expenditure (calories out). Energy expenditure is a measure of the total amount of energy (calories) that we need to expend, in order to meet our daily needs. Our energy expenditure can be broken down further into 4 components that combine to make up our total daily energy expenditure (TDEE). The four components of energy expenditure include our basal metabolic rate (BMR), exercise activity thermogenesis (EAT), non-exercise activity thermogenesis (NEAT), and thermal effect of food (TEF) (Gunga, 2020). Each component is responsible for a different portion of our TDEE, which allows us to understand what types of activity most of our calories are being allocated too. The first component of our energy expenditure is our basal metabolic rate (BMR). BMR is a measure of the amount of energy expended to keep the body functioning at rest. This includes many autonomous functions like heartrate, respiration, digestion, and the maintenance of cellular functions. BMR is also known as our body's metabolism and contributes to about 70% of our TDEE. The factors that determine our BMR include: sex, weight, height, age, ethnicity, weight history, body composition, and genetic factors. Of these factors, changes in weight and body composition such as losing body fat and increasing muscle mass, are the most effective methods that can increase our energy expenditure from our metabolism (BMR). The next component of our energy expenditure is our non-exercise activity thermogenesis (NEAT). NEAT is a measure of the amount of energy expended for all the activity we do that is not sleeping and exercise. This includes all the calories we expend walking, cooking, cleaning, touching our phone screens, making hand gestures, and brushing our teeth throughout the day. Our NEAT movement makes up about 66% of our day, assuming we sleep 8 hours a night, and contributes to about 15% of our TDEE. Since the majority of our waking day is consumed with NEAT movement, it has the most substantial impact on our activity energy expenditure. However, it is important to note that NEAT is one of our compensatory behaviors where when we are in a caloric deficit, our NEAT movements like twitching and standing tend to decrease to preserve calories. Therefore, engaging in moderate to high occupational-related physical activity, is the most effective method that can increase energy expenditure from NEAT movement. The third component of our energy expenditure is the thermic effect of food (TEF). The TEF is a measure of the amount of energy expended for the digestion, absorption, and disposal of ingested nutrients. This supports the concept that not all calories are the same, as calories from fat take about 0-5% of its calories to digest, calories from carbohydrates take about 5-15% of its calories to digest, and calories from protein take about 20-30% of its calories to digest. The TEF contributes to about 10% of our TDEE which varies between each person depending on the macronutrient composition of our meals. Other characteristics that have an impact on our TEF are age, level of physical activity, and level of insulin resistance. In addition, eating meals slowly and chewing our food more increases our TEF expenditure. However, the most effective way to increase our energy expenditure from the TEF and optimize our overall health is to eat high-protein whole foods, that will make it easier to lose weight and build lean body mass. The fourth and final component of our energy expenditure is our exercise activity thermogenesis (EAT). This contrasts with our non-exercise activity thermogenesis (NEAT) and measures the amount of energy expended from exercise-related physical activity. This includes all the calories we expend running, swimming, and lifting weights throughout each workout. Our EAT only contributes to about 5% of our TDEE and varies between each person depending on the length and intensity of our workouts. We often only focus on our EAT movement when we want to increase our TDEE, even though EAT movement makes up the smallest portion of our total energy expenditure. It is important that when we implement methods to increase our TDEE, we consider all components of our energy expenditure to elicit better results and improve our overall health.
The components of biochemistry that focus on caloric intake and caloric expenditure have been discussed. However, how does our body make energy from the calories we consume and how does that energy get expended once it is created? Cellular respiration is a component in the biochemistry of health which focuses on how our body creates energy from the calories we consume. Cellular respiration is a set of metabolic processes and reactions where biochemical energy is harvested from the nutrients we consume (glucose), and then is stored in energy carrying molecules (Adenosine Triphosphate). These metabolic processes are carried out in the cells of all living organisms to produce vital energy and sustain life. Cellular respiration can be divided into aerobic cellular respiration, anaerobic cellular respiration, aerobic lipolysis, and ATP phosphocreatine, which each produce different amounts of adenosine triphosphate (ATP), and are used depending on the physiological conditions of the body (Smith, 2021). Aerobic cellular respiration requires glucose and oxygen for the process to take place. There
are 4 stages of aerobic cellular respiration which include glycolysis, pyruvate oxidation, the citric acid or Krebs cycle, and the electron transport chain (Lumen, 2021). Each stage aims to produce ATP, which functions as a biological energy currency for cells to store and use for chemical reactions. The first stage of aerobic cellular respiration is glycolysis, and this is where glucose is broken down in the cytoplasm. After a series of chain reactions this stage produces a net gain of 2 ATP, 2 NADH, and 2 pyruvate molecules. NADH is a coenzyme central to metabolism and pyruvate is formed from the break down of a glucose molecule (a six-carbon molecule) into 2 smaller pyruvate molecules (a three-carbon molecule). The second stage of aerobic cellular respiration is pyruvate oxidation, and this is the stage that begins in the mitochondria, linking the first stage to the third stage. The pyruvate molecules produced from the break down of glucose pass into the mitochondria, where 1 carbon dioxide molecule and 1 hydrogen molecule are removed. This produces an acetyl group, which joins to an enzyme called CoA (Coenzyme A) to form acetyl-CoA. ATP is not produced during the pyruvate oxidation stage, but acetyl-CoA and more NADH is produced to be used during the third stage. The third stage of aerobic cellular respiration is the citric acid or Krebs cycle. This stage continues in the mitochondria and consists of a chain of eight reactions that form a cycle. This cycle produces 2 carbon dioxide molecules, 3 NADH molecules, and a molecule of FADH2. Since each glucose breaks down into 2 pyruvate, and 2 pyruvate produce 2 acetyl-CoA, and only 1 acetyl-CoA is used per Krebs cycle, two Krebs cycles are required per glucose molecule producing a net gain of 4 carbon dioxide molecules, 6 NADH molecules, and 2 molecules of FADH2. The final stage of aerobic cellular respiration is the electron transport chain, where most ATP production occurs. The NADH and FADH2 molecules which all gained an electron from the Krebs cycle, transfer their electrons to the inner membrane of the mitochondria. These electrons provide the energy that activates a chain of channel proteins along the membrane, the electron transport chain. These channel proteins use the energy from the electrons to pump hydrogen protons from the center of the mitochondria to the outside of the mitochondria, where the concentration gradient will drive them to re-enter the mitochondria through channel proteins called ATP synthase. These ATP synthase channel proteins use the potential energy provided from the hydrogen protons re-entering the mitochondria, to phosphorylate adenosine diphosphate (ADP) (adds a phosphate group) and produce a net gain of 34 ATP. The FADH2 also produce 2 ATP bringing the total net gain of ATP from aerobic cellular respiration to about 38 ATP. Another form of cellular respiration is anaerobic cellular respiration, which does not require oxygen to produce ATP. This process occurs when we engage in intense exercise that requires more energy than the oxygen available can supply. Through anaerobic cellular respiration, our body breaks down glucose without oxygen and produces a net gain of 2 ATP. Compared to cellular aerobic respiration, cellular anaerobic respiration is quicker and occurs more often to meet the demand, as the lack of oxygen means less energy is produced for every glucose molecule that is broken down. Therefore, cellular anaerobic respiration is mostly used during vigorous exercise, when oxygen is not available and ATP needs to be produced quickly. This contrasts with aerobic cellular respiration which is mostly used during low-intensity activities, when ATP requirements are slow and steady and oxygen is available. Aerobic lipolysis is another form of cellular respiration that occurs in the cytoplasm and requires fat instead of glucose to produce ATP. Fat molecules (triglycerides) are broken down into fatty acid molecules through lipolysis, which get oxidized into acetyl-CoA to be used in the Krebs cycle (aerobic respiration). Since a single triglyceride produces 3 fatty acid molecules with about 16 carbons per fatty acid molecule, each fatty acid molecule produces a net gain of 100 ATP, or 300 ATP per triglyceride. Compared to cellular aerobic respiration and cellular anaerobic respiration which both use glucose, aerobic lipolysis is the slowest but most efficient method at yielding ATP per molecule of fat. Another concept to consider is that all muscle cells have small amounts of ATP and phosphocreatine stored inside them. When the muscle cells need immediate energy, ATP is broken down into ADP and a single phosphate molecule, releasing energy in the process. Then an enzyme called creatine kinase breaks down phosphocreatine into a creatine molecule and a phosphate molecule, also releasing energy in the process. This energy allows the ADP molecule and the single phosphate molecule to rejoin and form ATP, so it can be broken down for energy again in a cycle, until phosphocreatine stores are depleted in the muscles. Compared to aerobic cellular respiration, anaerobic cellular respiration, and aerobic lipolysis, the phosphocreatine method of producing ATP is the most similar to anaerobic cellular respiration, where it does not require oxygen and is mostly used during vigorous exercise, when ATP needs to be produced quickly. Understanding the different methods of cellular respiration, how food is metabolized for energy, and how that energy is expended, allows us to understand how to improve our nutrient consumption so we can optimize our energy metabolism and our overall health.
A popular component in the biochemistry of health focuses on how we build and grow muscle in our bodies. While there are three different types of muscles (skeletal, cardiac, and smooth muscle), when we talk about building and growing muscle we are referring to skeletal muscle. Skeletal muscle (muscle) tissue is a soft contractile tissue responsible for the posture and voluntary movement of the human body. They are attached to bones by tendons and grouped to cooperate with each other, to allow us to stand upright and produce movement efficiently. This allows us to interact with our environment and carry out the necessary tasks for survival. Muscle is the most adaptable tissue in the human body that we begin building when we are an embryo (Lumen, 2021). The cells in the embryo divide into three layers (endoderm, mesoderm, and ectoderm), that become the different tissues in our body, with the mesoderm becoming a variety of tissues including skeletal muscle. Cells in the mesoderm called myoblasts are the embryotic precursors of myocytes (muscle cells/fibers), that grow and replicate until they are ready to develop into muscle tissue. When myoblasts encounter signals from fibroblast growth factor, serum response factor, and calcium, they fuse into multi-nucleated myotubes, which later become muscle cells/fibers. Myoblasts that do not fuse together become muscle stem cells (satellite cells), that are involved in muscle growth, muscle regeneration, and muscle repair. The human body develops and maintains about the same amount of muscle cells/fibers throughout our lifespan, with each one getting bigger by satellite cells through hypertrophy. Muscle hypertrophy is defined as the increase in muscle cell/fiber size, typically as a result of a cellular adaptation to external stimuli. When we continually challenge our muscles with a progressive overload of weight and/or resistance, our muscle cells/fibers experience microscopic damage, causing them to elicit an inflammatory response (Chargé & Rudnicki, 2004). This response activates satellite cells to repair or replace the damaged muscle cells/fibers by joining together and fusing into the cells/fibers, increasing its size each time. The process of muscle hypertrophy occurs under the conditions that: 1) we are stimulating the muscle enough to cause enough microscopic damage that can result in muscle growth, 2) we are giving our muscles enough nutrients and rest so the rate of protein synthesis exceeds the rate of protein breakdown, and 3) our hormones like testosterone, human growth hormone, and insulin growth factor are able to enhance muscle tissue growth. However, muscle tissue is energy hungry and requires even more nutrients to maintain them as they grow in size and capacity. Our muscles spend a significant amount of resources converting chemical potential energy to mechanical energy, as they contract and relax (Pham & Puckett, 2021). This mechanism occurs inside the muscle cells/fibers on the myofibrils that form our muscle cells/fibers, on the sections divided lengthwise called sarcomeres. Each sarcomere (separated by a Z-line) contains two types of myofilaments called actin (thin filaments) and myosin (thick filaments), which are proteins that extend lengthwise and provide the means for muscle contraction and muscle relaxation. A muscle contraction occurs when action potentials travel from the motor neurons, through the neuromuscular junctions, and onto the muscle cells/fibers. This causes the release of the neurotransmitter acetylcholine (ACh), which binds to receptors on the muscle cells/fibers and initiates a chemical reaction. The binding of ACh opens sodium (Na) ion channels to allow sodium into the cytoplasm of the muscle cells/fibers. The influx of sodium triggers the release of stored calcium ions, which diffuse into the muscle cells/fibers. The presence of calcium and the energy obtained from ATP allows actin filaments and myosin filaments to slide past one another towards each other, bringing the Z-lines of the sarcomeres closer together and creating a muscle contraction. When the stimulation from the motor neurons stop, the actin filaments and myosin filaments slide past one another away from each other, sending the Z-lines of the sarcomeres farther away to their original positions and creating muscle relaxation. Since this process occurs anytime our muscle contracts, our muscle cells/fibers efficiently reset themselves in preparation for the next round of stimulation, such as restocking calcium stores and receiving more ATP from muscle cell/fiber mitochondria. To avoid exhausting our muscle cells/fibers before our body meets the demand, it is important that we routinely engage in hypertrophy training while also consuming proper nutrition, to ensure we are optimizing muscle performance and our overall health.
"Biochemistry is the science of life. All our life processes - walking, talking, moving, feeding - are essentially chemical reactions. So biochemistry is actually the chemistry of life, and it's supremely interesting."
