Food to Energy Production

Whatever we do, whether we think, talk, listen, understand or even walk, every activity requires energy from food. The process of food-to-energy production occurs through different chemical reactions, which collectively refer to the metabolism or enzymatic process. The food we eat is a complex material that must be a breakdown for energy production. This breakdown of food occurs through metabolism, which completes in three stages. The first stage of food metabolism takes place in our digestive system. In this stage, our digestive organs degrade, digest and convert complex food material and nutrients into simple molecules. The second and third stage of food metabolism occurs in our body cells that further break down simple molecules to produce energy.

Interesting Fact

Do you know how many digestive systems are present in our body? This is not the correct answer if you think we have only one digestive system. Every human has two digestive systems. We are familiar with the digestive system, which starts from the mouth and ends at the anus. At the same time, the second digestive system is present inside our body cells, called the digestive system of the cell. Small structures, the organelles, are present in our body cells. One of the organelles is lysosomes (Figure 1). They are the cell’s digestive system because they contain enzymes that can degrade and digest complex foreign particles, including infectious viruses and bacteria that enter the cell.

Let’s discuss three stages of the metabolic process.

First Stage

The food contains four different macromolecules, including carbohydrates, proteins, vitamins and fats. Our digestive system digests and convert these macromolecules into simple molecules. Here is the end of the first stage of the metabolic process. These simple molecules move from the small intestine into the bloodstream, which blood transports to body cells for energy production. Food-to-energy production is a complex process. We have discussed the digestive system and organs (video and article). Observing the chemical nature of food, the food also contains many nutrients called essential nutrients. These nutrients cannot produce in our bodies. Instead, they are only consumed through food. These nutrients are present in two forms: essential organic and inorganic. Vitamins and fatty acids like omega-3 and omega-6 are essential organic nutrients. While minerals are essential inorganic nutrients.

Minerals are also called co-factors, and they play an important role in the structure and regulatory functions of the body. A few essential minerals include calcium, chloride, iron, copper, iodine, magnesium, potassium, selenium, sodium, zinc, etc. Similarly, some amino acids are essential nutrients that human body cannot produce. Methionine, leucine, isoleucine, valine, lysine, threonine, arginine, histidine, tryptophan and phenylalanine are ten essential amino acids that humans must need to consume through food.

Role of Hormones and Nerves

The first stage of the metabolic process that occurs in the digestive system (Figure 2) is more complex than it looks alike. It can be understood by observing the physiology of the human body that hormones and nerves play a critical role in regulating and controlling every body function. In the digestive system, specific cells are present in the stomach lining and small intestine. These cells release hormones that stimulate gastric juices in the stomach and bile and pancreatic juices in the small intestine. These hormones control our digestive system’s function and regulate our hunger mechanism.

Besides hormones, two types of nerves control the action of our digestive system. These nerves include extrinsic and intrinsic nerves. Extrinsic nerves are nerves do not present inside the digestive system, but they connect our digestive organs to the brain and spinal cord. These nerves release specific chemicals that control muscular contractions and relaxations in our digestive tract as per food digestion needs. Intrinsic nerves are present inside our digestive tract and become active during food movement. These nerves release chemicals that are essential to food movement from the intestine.

End of First Stage of Enzymatic Process

At the end of the first stage of the metabolic process, digested food molecules, minerals and water enter the bloodstream from the small intestine. The blood transports all these materials and water to different body parts for energy production or storage. Amino acids, glycerol, simple sugars like glucose and some vitamins and salts are direct transport through the portal vein into the liver. While free fatty acids bind to albumin protein, and cholesterol binds to lipoproteins in the small intestine. These now albumin and lipoproteins bonded fatty acids, cholesterol, and some vitamins first enter the lymphatic system and then the bloodstream from the small intestine. The second stage of the metabolic process starts when digested food nutrients enter the body cells from the blood.

Second and Third Stage

The second metabolic process stage occurs in the body cells’ cytoplasm. In this stage, glucose breaks down through glycolysis into two pyruvate molecules with the release of ATP (adenosine triphosphate) and NADH. Here is the end of the second stage, and two pyruvate molecules move from the cytoplasm into the mitochondria. Mitochondria is the energy house of a cell in which two pyruvate molecules enter the oxidation process separately. This way, pyruvate is to acetyl-coenzyme A and oxaloacetate is produced. Oxaloacetate then enters the citric acid cycle, leading to the production of many NADH molecules. The NADH molecules undergo further processing to form ATP. At the end of these processes, ATP molecules are packed in special packets that can easily transport to different sites.

Interesting Fact

Do you know how many ATP molecules are present at a given time in a cellular solution, and what is their utilization time? Approximately 10⁹ (one billion) ATP molecules are present at any given time in a cellular solution. These ATPs are consumed and utilized every 2-3 minutes and replaced by the new ATP molecules.