Metabolism

Metabolism is the process by which food substances undergo chemical reactions within the living cells, catalyzed by enzymes and regulated by hormones and vitamins.

Pathways 

metabolism involves a series of chemical reactions, known as metabolic pathways.in general, the first steps take place in the cytosol, where the enzymes break down large organic molecules previously assembled by the cell( such as proteins, and glycogen) into smaller fragments that join the nutrition pool. e.g. glycolysis, citric acid cycle, oxidative phosphorylation,glycogenesis,glycogenolysis.

Basal metabolic rate (BMR) 

Your basal metabolic rate (BMR) is the minimum amount of calories your body requires to sustain basic functions at rest, and it differs among individuals. It typically accounts for 60% to 70% of your total energy expenditure. When you undergo rapid weight loss or adopt aggressive calorie restriction, your BMR can decrease. This phenomenon partly explains why weight loss often isn’t a steady process and may plateau at times.

Factors influencing metabolism

Factors influencing metabolism encompass a variety of elements, some modifiable and others immutable:

  • Genetics: The energy requirements of your body are influenced by a set of genetic factors. Individuals with larger body sizes typically possess greater muscle mass and thus necessitate more calories. Men, characterized by lower body fat and higher muscle mass, tend to require increased caloric intake.
  • Age: Contrary to common belief, age itself doesn’t primarily cause a decline in metabolism. Rather, factors such as decreased physical activity, diminished muscle mass, and potential dietary inconsistencies as one ages contribute to a slower metabolic rate.
  • Diet: While there are no miraculous foods or diets to maintain metabolism, dietary choices can still impact it positively. Consuming good carbohydrates, appropriate calorie amounts, and consistent meals supplies the body with the necessary energy.
  • Intermittent Fasting: This popular dietary approach entails consuming food during a predetermined window of time each day, typically around 8 hours, with fasting for the remainder. Once the body exhausts ingested energy, it turns to stored fat for fuel, potentially aiding in eliminating excess stored fuel. Intermittent fasting shows promise for weight loss, heart health, diabetes, and obesity management, but choosing a plan aligned with individual health and consulting a doctor beforehand is prudent.
  • Sleep: Adequate sleep plays a vital role in regulating blood sugar levels. Poor sleep patterns disrupt glucose regulation, leading to diminished energy levels. Establishing consistent sleep routines, refraining from caffeine and nicotine before bed, and avoiding blue light exposure from electronic devices promote quality sleep.
  • Exercise: Physical activity is a cornerstone for optimizing metabolism, as movement expends the most energy and burns calories. Even moderate activities like short walks contribute to metabolic boost, aiding in utilizing excess energy, fat burning, and enhancing cardiovascular health. Incorporating muscle-strengthening exercises is crucial for maintaining healthy muscle mass and minimising risk factors associated with common metabolic disorders.

 

Metabolic disorders 

Metabolic disorder encompasses a range of conditions that disrupt normal metabolic processes, often due to genetic mutations or enzyme deficiencies. Some examples of metabolic disorders include:

  • Phenylketonuria (PKU): Individuals with PKU lack the enzyme necessary to break down the amino acid phenylalanine, leading to its accumulation in the body and potential neurological damage if untreated.
  • Galactosemia: This disorder results from the inability to metabolize galactose, a sugar found in dairy products, due to enzyme deficiencies. Accumulation of galactose can cause liver damage, kidney problems, and other complications if not managed.
  • Prader-Willi syndrome: Characterized by insatiable hunger and a lack of satiety, individuals with Prader-Willi syndrome often face obesity-related health issues. The exact cause of this syndrome is not fully understood.

Metabolic syndrome, on the other hand, refers to a cluster of metabolic abnormalities and risk factors that increase the likelihood of developing cardiovascular disease, type 2 diabetes, and stroke. These risk factors include:

  • High blood pressure: Elevated blood pressure increases the strain on the heart and blood vessels, raising the risk of cardiovascular events.
  • High blood sugar: Elevated blood glucose levels indicate poor glucose regulation and can lead to diabetes and other complications.
  • Abdominal obesity: Excess fat around the waist or abdomen is associated with insulin resistance and an increased risk of metabolic and cardiovascular diseases.
  • High cholesterol: Elevated levels of LDL cholesterol (“bad” cholesterol) and triglycerides, along with low levels of HDL cholesterol (“good” cholesterol), contribute to plaque buildup in the arteries, increasing the risk of heart disease and stroke.

Metabolic syndrome is often linked to lifestyle factors such as poor diet, sedentary behaviour, and obesity, highlighting the importance of adopting healthy habits to prevent or manage these conditions.

 

Control metabolism

Various hormones within the endocrine system regulate the pace and direction of metabolism. Thyroxine, produced and released by the thyroid gland, plays a vital role in determining the speed of metabolic chemical reactions in the body.

The pancreas, another important gland, releases hormones that dictate whether the body’s primary metabolic activities lean towards being anabolic or catabolic. Typically, after a meal, there’s an increase in anabolic activity due to elevated glucose levels in the bloodstream triggered by eating. The pancreas detects this surge and releases insulin, prompting cells to heighten their anabolic functions.

Metabolism is a complex biochemical process often simplified as the mechanism influencing weight gain or loss. This process involves calories, which measure the energy a specific food provides to the body. Foods like chocolate bars, rich in calories, offer substantial energy, potentially leading to excess if consumed excessively. Just as a car’s gas tank stores fuel until needed, the body stores calories, primarily as fat. Overconsumption of calories results in the accumulation of excess body fat, akin to spilling fuel onto the pavement.

The daily calorie expenditure of an individual is influenced by factors such as exercise level, body composition (including fat and muscle ratio), and basal metabolic rate (BMR). BMR gauges the rate at which the body consumes energy, or calories, while at rest.

BMR’s significance extends to its impact on weight gain tendencies. Individuals with lower BMRs, burning fewer calories during rest or sleep, are prone to accumulating more body fat over time compared to those with average BMRs, given similar dietary and exercise habits.

BMR can be influenced by genetic factors and certain health conditions, as well as by body composition, where individuals with more muscle and less fat typically exhibit higher BMRs. However, lifestyle changes like increased physical activity not only boost calorie expenditure but also enhance physical fitness, contributing to higher BMRs.

Carbohydrate, lipid, protein metabolic process 

Carbohydrate metabolism

Carbohydrate metabolism encompasses the biochemical processes involved in the creation, breakdown, and conversion of carbohydrates within living organisms. 

Plants utilise photosynthesis to synthesise carbohydrates from carbon dioxide and water, storing energy derived from sunlight internally. When animals and fungi consume these plants, cellular respiration breaks down the stored carbohydrates, making energy available to cells. Both animals and plants store the released energy temporarily in high-energy molecules like adenosine triphosphate (ATP) for various cellular functions.

All ingested carbohydrates are converted to glucose.it is absorbed into the blood and is transported to the liver for use in several metabolic ways.

Pathways

  • Glycolysis: it is the breakdown of glucose molecules to pyruvate in the cytoplasm of a cell. It is an anaerobic process because it does not require oxygen.the net reaction of glycolysis is as follow: Glucose+ 2NAD+2ADP+2→ 2 Pyruvate+NADH+2 ATP the glycolysis provides a net gain of 2 molecules of ATP for each glucose molecule.
  • Glycogenesis It is the formation of glycogen from glucose in the liver and in the skeletal muscle.  Glucose⇄ Glycogen
  • Lipogenesis It is the process of converting excess glucose to lipid
  • Gluconeogenesis Gluconeogenesis (GNG) is a metabolic pathway found across various organisms, including plants, animals, fungi, bacteria, and other microorganisms. It involves the synthesis of glucose from specific non-carbohydrate carbon sources.
  • Metabolism of protein

Proteins are absorbed as amino acids and carried by the portal circulation to the liver and then to the whole body by general circulation. The body can not store amino acids. instead, it converts them to protein or glucose or catabolizes them to provide energy. Before they change, amino acids must be transformed by deamination or transamination.

Metabolism of fat

Fat often receives criticism as a primary factor in the global obesity epidemic, attributed in part to the widespread adoption of fast-food diets exported by the United States. These dietary habits contribute to the rise in body mass index (BMI), associated with various health risks. Recent research highlights the significance of fat distribution in health outcomes, with individuals harbouring excess abdominal fat facing heightened risks of cancer and cardiovascular diseases. The intricate biology of fat, synonymous with lipids, is essential for cellular homeostasis, contributing to ATP generation, synthesis of vital molecules like vitamins and hormones, and regulation of cellular signalling. Cholesterol and phospholipids, crucial components of cell membranes, underscore the importance of lipid metabolism, which is compartmentalised between anabolism in the cytosol and endoplasmic reticulum, and catabolism primarily in mitochondria. This review will delve into three fundamental aspects of lipid biology: lipid production, catabolism for ATP generation, and their roles as signalling molecules.