How do cells get energy from food?

The human body is a complex biological machine, always requiring energy to perform all life functions from maintaining heart rate to muscle movement. But how can the body convert food into energy? The article below will clearly state how cells get energy from food?

1. How food provides energy to the body through nutrient groups 

The food we consume every day is the main source of energy for the body. Nutrient groups such as carbohydrates, proteins, and lipids (fats) play an important role in providing energy to maintain life activities. When digested, these nutrients are broken down into smaller compounds, which are then used by cells to produce ATP (adenosine triphosphate), a form of energy that the body can use. In particular, glucose from carbohydrates is the main source of energy for cells, but proteins and lipids also play an important role, especially when carbohydrates are lacking.

1.1. Carbohydrates: Main source of energy

Carbohydrates are the fastest and most important source of energy for the body. These include simple sugars such as glucose and complex starches. After eating, carbohydrates are broken down into glucose, which is then absorbed into the blood. Glucose is transported to cells throughout the body, where it participates in glycolysis. Here, glucose metabolism into pyruvate, generating a small amount of ATP. Pyruvate then continues into the Krebs cycle and electron transport chain, where the majority of ATP is produced.

• Glucose: Glucose is the main source of energy for cells. When glucose is broken down, it provides energy to all cells, especially high energy consuming organs such as the brain and muscles.
• Glycogen: The body stores some glucose in the form of glycogen, mainly in the liver and muscles. When energy needs increase (as during physical activity), glycogen is broken down into glucose to provide quick energy.

1.2. Proteins: Replacement and repair roles

Protein is not the body’s main source of energy but can act as an energy source when carbohydrates are lacking. Protein from food is broken down into amino acids, which can then be used to produce energy if needed. Some amino acids can be converted to glucose through gluconeogenesis in the liver, providing energy to cells when carbohydrates are insufficient.

Additionally, protein has a key role in repairing and building tissue, making important enzymes and hormones, and not just being an energy source.

• Gluconeogenesis: This process takes place when the body needs energy but lacks a supply of carbohydrates. Amino acids from protein will be converted into glucose to provide energy.

1.3. Lipids (Fat): Source of stored energy

Lipids are a source of long-term energy storage and have the highest energy density. Fat is stored as triglycerides in adipose tissues. When the body needs energy but glucose is limited (such as during fasting or prolonged exercise), fat is broken down into fatty acids and glycerol. The fatty acid is then metabolized in the β-oxidation cycle to produce acetyl-CoA, which continues into the Krebs cycle to produce ATP.

• Acetyl-CoA: From fatty acids, acetyl-CoA is created and provides long-lasting energy to the body. This process is especially effective in supplying energy to the heart muscle and during prolonged activities when carbohydrates are scarce.
• Ketones: When carbohydrate intake is too low, the body converts fat into ketones to fuel the brain and other organs, a state called ketosis.

1.4. Glucose: Main source of energy for cells

Glucose is the simplest sugar, easiest for cells in the body to use. After being absorbed into the blood, glucose will be transported to cells and participate in glycolysis and subsequent chain reactions to create ATP. This is the process of quickly providing energy to cells and maintaining the body’s daily activities.

• Glycolysis: This process takes place in the cell’s cytoplasm and breaks down glucose into pyruvate, rapidly producing ATP.
• Krebs Cycle and Electron Transport Chain: Pyruvate from glycolysis is transferred to the mitochondria, where the Krebs cycle and electron transport chain processes produce most of the energy in the form of ATP.

2. The process of digesting and absorbing nutrients to turn them into energy for cells

How does food turn into energy? When we consume food, the body must go through a series of digestion and absorption processes to convert nutrients into energy that cells can use. Carbohydrates, proteins, and lipids (fats) are each processed through different pathways, but all have the same goal of creating ATP (adenosine triphosphate), the cell’s main form of energy. Below is how nutrient groups are digested, absorbed and turned into energy for the body.

2.1. Digestion and absorption of carbohydrates

Digest

• Carbohydrate digestion begins in the mouth with the enzyme amylase in saliva, which breaks down large starch molecules into simpler sugar molecules like maltose.
• When carbohydrates move to the stomach, the enzyme amylase is inactive in the acidic stomach environment. Then, in the small intestine, the pancreatic amylase enzyme continues to break down carbohydrates into simple sugars such as glucose, fructose, and galactose.
• Finally, enzymes from the lining of the small intestine such as maltase, sucrase, and lactase break down double sugar molecules into single sugars such as glucose, which can be absorbed into the bloodstream.

Absorb

• Glucose, the main product of carbohydrate digestion, is absorbed into the cells of the lining of the small intestine through special transport channels, then into the blood. From here, glucose is transported to cells throughout the body, especially the muscles and brain.
• Insulin, a hormone produced by the pancreas, helps regulate the absorption of glucose into cells, where it is metabolized to produce energy.

Converted into energy

• Glycolysis: In cells, glucose undergoes glycolysis in the cytosol, where it is broken down into pyruvate and produces small amounts of ATP.
• Krebs Cycle and Electron Transport Chain: Pyruvate is then transferred into the mitochondria, where it continues through the Krebs cycle and electron transport chain, generating the majority of the ATP needed by the body.

2.2. Protein digestion and absorption

Digest

• Protein begins the digestive process in the stomach, where the enzyme pepsin works in an acidic environment to break down large polypeptide chains into smaller molecules.
• As the proteins move down to the small intestine, enzymes from the pancreas, such as trypsin and chymotrypsin, continue to break them down into smaller amino acids.
• Finally, peptidase enzymes in the small intestine wall break down the remaining polypeptides into individual amino acids, ready for absorption.

Absorb

• Amino acids are absorbed through the cells lining the small intestine and enter the bloodstream. From here, they are transported to the liver and other tissues to synthesize new proteins, support growth, tissue repair, or participate in energy production.

Converted into energy

• When necessary, especially under conditions of carbohydrate deficiency, amino acids can be converted to glucose through gluconeogenesis in the liver.
• Amino acids can also be converted directly into energy through the Krebs cycle after they have had their amino group removed, although proteins are not the body’s main source of energy.

2.3. Digestion and absorption of lipids (fats)

Digest:

• Lipid digestion begins in the mouth and stomach with some degradation by the enzyme lipase. However, the main digestion process takes place in the small intestine.
• When fat enters the small intestine, bile from the liver and gallbladder is secreted to emulsify the fat, turning it into smaller droplets that are easier to digest.
• Pancreatic lipase then breaks down triglycerides into fatty acids and glycerol, forms that can be absorbed.

Absorb:

• Fatty acids and glycerol are absorbed into cells lining the small intestine and assembled into more complex lipid molecules called chylomicrons, which are then transported into the lymphatic system and then into the blood to provide energy. or stored in adipose tissue.

Converted into energy:

• When the body needs energy, fat is broken down into fatty acids and glycerol. Fatty acids undergo β-oxidation in the mitochondria, generating acetyl-CoA, which then enters the Krebs cycle to produce ATP.
• Lipids are a long-term energy reserve, and fat breakdown helps provide sustained energy when the body is lacking glucose.

2.4. The role of nutrient groups in energy metabolism

• Carbohydrates: Is the main and quick source of energy, especially glucose, the main source of energy for the brain and muscles.
• Protein: Primarily used to build and repair muscles, tissues and enzymes, but can also provide energy when needed.
• Lipids: Are long-term stored energy sources and have the highest energy density, helping to provide energy for long periods or when carbohydrate supplies are depleted.

3. The role of fat and protein in energy production

Fats and proteins play an important role in the body’s energy production process. but they are used differently and have distinct roles.

• Role of fat:

• • • Stored energy source: Fat is the body’s most abundant source of energy, providing about 9 kcal/gram. When carbohydrates are not enough to provide energy, the body will switch to burning fat.
    • Beta-oxidation: Fats are broken down into free fatty acids and glycerol, which then undergo beta-oxidation in the mitochondria to produce Acetyl-CoA, which further participates in beta oxidation. Participates in the Krebs cycle (citric acid cycle) to produce ATP, the cell’s main energy source.
    • Energy during long-term exercise: When exercising or exercising for a long time, the body will rely more on fat to create energy.

• Role of proteins:

• • Substrate for gluconeogenesis: Protein is not the body’s main source of energy, but in case of carbohydrate and fat deficiency, protein can be broken down into amino acids. Some amino acids can be converted to glucose through gluconeogenesis to provide energy.
  • Preserving muscle tissue: Protein plays a key role in building and maintaining muscle tissue, however, in emergency situations, when other energy sources are insufficient, the body can metabolize protein from muscle. corn into energy.
  • ATP production via Krebs cycle: Amino acids from proteins, after being metabolized, can participate in the Krebs cycle, contributing to ATP production.

Fat is the main source of stored energy and is important during long-term activities, while protein has a secondary role and is often used in situations of energy deficiency.

In short, our body is a complex system with possibilities convert food into energy through sophisticated biochemical processes. From carbohydrates to fats to proteins, each nutrient plays a certain role in providing energy to cells. Through the process of digestion and absorption, nutrients are converted into smaller molecules such as glucose, fatty acids, and amino acids. These molecules then undergo a metabolic cycle within the cell, primarily the cellular respiration cycle, to produce ATP, the body’s main source of energy.

Carbohydrates provide a quick source of energy through glycolysis, while fats store long-term energy and proteins serve a supporting role when needed. Understanding How cells get energy from food not only helps us maintain a healthy lifestyle but also supports optimizing nutrition to suit the body’s daily energy needs.

References: Ncbi.nlm.nih.gov, Bio.libretexts.org, Nature.com, Quizlet.com, Msdmanuals.com, Wildnutrition.com