Energy Metabolism

Glycolysis

What it means: Breakdown of glucose → pyruvate (for energy)

Direction: Glucose → energy

What it means: Fed state, ongoing energy production

Glycogenesis

What it means: Formation of glycogen from glucose (storage)

Direction: Glucose → glycogen

What it means: Fed state, when glucose is abundant (e.g., after a meal)

Glycogenolysis

What it means: Breakdown of glycogen back into glucose

Direction: Glycogen → glucose

What it means: Early fasting/between meals, when blood glucose starts to drop

Gluconeogenesis

What it means: Making new glucose from non-carb sources (amino acids, glycerol, lactate)

Direction: Non-carb → glucose

What it means: Prolonged fasting, once glycogen stores are depleted

Ketogenesis

• Catabolic

• Triggered when glucose is unavailable (prolonged fasting, low-carb/ketogenic diets, uncontrolled Type 1 diabetes)

• Fat breaks down → excess acetyl-CoA → converted to ketone bodies (beta-hydroxybutyrate, acetoacetate) when Krebs cycle capacity is exceeded

• Brain adapts to use ketones as fuel after ~3 days of fasting

Insulin

• Anabolic hormone

• Lower blood glucose

Glucagon

• Catabolic hormone

• Raise blood glucose

De novo lipogenesis

• converting glucose to fat

• Excess glucose is converted → acetyl-CoA → fatty acids → triglycerides → stored in adipose tissue

Lipolysis