Biochemistry, Ketogenesis

Excerpt

The primary energy source shifts from glucose to fat during periods of fasting or starvation, when carbohydrate intake is markedly reduced. Adipose tissue releases stored triglycerides, which are hydrolyzed into free fatty acids (FFAs) and glycerol. FFAs are transported to the liver, where they undergo β-oxidation, generating large amounts of acetyl-CoA.

Accumulation occurs when acetyl-CoA production exceeds the liver’s oxidative capacity in the citric acid cycle. This imbalance is partly driven by decreased availability of oxaloacetate, which is diverted toward gluconeogenesis. Excess acetyl-CoA cannot be fully oxidized or redirected into fatty acid synthesis. The metabolic bottleneck channels acetyl-CoA into ketogenesis, in which the liver converts acetyl-CoA into ketone bodies, primarily acetoacetate and β-hydroxybutyrate (see Image. Ketogenesis Pathway).

Ketone bodies are released into the circulation and serve as an alternative energy substrate for peripheral tissues, particularly the brain, during prolonged carbohydrate deficiency. Plasma concentrations rise when the rate of ketone body production surpasses peripheral utilization, resulting in ketonemia. Progressive accumulation leads to urinary excretion, termed "ketonuria."

Marked ketonemia and ketonuria are most frequently associated with uncontrolled type 1 diabetes mellitus. In this setting, absolute insulin deficiency limits glucose uptake, promotes unregulated lipolysis, and accelerates ketogenesis. The resulting overproduction of acidic ketone bodies can exceed the buffering capacity of blood, causing metabolic acidosis. This condition, known as diabetic ketoacidosis (DKA), constitutes a serious and potentially life-threatening complication requiring prompt treatment.

Mastery of the ketogenesis pathway enables clinicians to link biochemical findings with clinical presentations. This integrative approach enhances decision-making in metabolic, endocrine, and nutritional disorders.