Metabolism of Exercise and Starvation

Introduction – Metabolism of Exercise and Starvation

Metabolism refers to the processes by which the body converts food into energy and builds and repairs cells and tissues. Two common conditions that affect metabolism are exercise and starvation.

Exercise is a physical activity that increases energy expenditure and oxygen consumption. During exercise, the body’s metabolism shifts from using primarily carbohydrates and fats for energy to using predominantly carbohydrates. This is because carbohydrates can be broken down into glucose, which is readily available for use as energy by the muscles. However, as the duration of exercise increases, the body’s carbohydrate stores become depleted, and it begins to break down stored fats for energy.

Metabolism of Exercise States

• 100 meter sprint
  • energy source used
    • pre-synthesized ATP
    • creatine phosphate
    • anaerobic glycolysis
• 100 meters to 1 kilometer
  • energy source used
    • oxidative phosphorylation
• 1 kilometer to a marathon
  • energy source used
    • glycogen
• β-oxidation of fatty acids

Metabolism of Exercise States

• Absorptive state
  • immediately after eating
  • insulin in control
    • insulin-sensitive tissues
      • adipocytes
      • myocytes
      • hepatocytes
    • pathways favored by insulin
      • glycogenesis
      • fatty acid synthesis
      • glucose uptake in fat, muscle, liver
      • protein anabolism
    • insulin-resistant tissues
      • brain
      • RBCs
• Post-absorptive state
  • between meals
  • epinephrine/glucagon in control
    • glucagon-sensitive tissues
      • adipocytes
      • hepatocytes
    • pathways favored by glucagon
      • glycogenolysis
      • fatty acid catabolism
      • protein catabolism
      • gluconeogenesis
    • glucagon-resistant tissues
      • brain
      • RBCs
• Starvation
  • days 1-3
    • main source of energy for body
      • catabolism of triglycerides in fat stores
    • main source of energy for brain
      • glucose from gluconeogenic conversion of lactate and alanine
  • > 3 days
    • main source of energy for body
      • catabolism of triglycerides in fat stores
    • main source of energy for brain
      • mostly glucose with some ketone bodies
  • > several weeks
    • main source of energy
      • degradation of muscle and organs
        • after adipose tissue store have been exhausted
    • main source of energy for brain
      • 2/3 ketone bodies
      • 1/3 glucose
• note: RBCs are always dependent on glucose

Symptoms – Metabolism of Exercise and Starvation

The symptoms of metabolism during exercise and starvation can vary depending on the severity and duration of the condition. Here are some common symptoms associated with each condition:

Exercise:

• Increased heart rate and breathing
• Sweating
• Fatigue
• Muscle soreness
• Hunger
• Thirst
• Increased body temperature

Starvation:

• Fatigue and weakness
• Dizziness and lightheadedness
• Headaches
• Low blood sugar levels
• Decreased body temperature
• Muscle wasting
• Malnutrition
• Dehydration

It is important to note that engaging in regular exercise and maintaining a balanced diet can help prevent the negative effects of starvation on the body’s metabolism. Additionally, it is recommended to seek medical attention if symptoms become severe or persistent.

Studies

There have been many studies conducted on the metabolism of exercise and starvation. Here are a few examples:

Exercise:

• A study published in the Journal of Applied Physiology found that endurance exercise can increase the body’s ability to use stored fats for energy during exercise, which can improve overall physical performance.
• Another study published in the Journal of Strength and Conditioning Research found that resistance exercise can increase muscle mass and strength, as well as improve metabolic health markers such as insulin sensitivity.

Starvation:

• A study published in the Journal of Clinical Endocrinology and Metabolism found that prolonged starvation can lead to a decrease in resting metabolic rate, which can contribute to weight gain after resuming normal eating habits.
• Another study published in the American Journal of Clinical Nutrition found that prolonged starvation can lead to muscle wasting and a decrease in muscle protein synthesis, which can contribute to overall weakness and decreased physical performance.

Overall, these studies demonstrate the importance of maintaining a balanced diet and engaging in regular physical activity to support a healthy metabolism and prevent negative health outcomes associated with both exercise and starvation.

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