How does the liver use fatty acids when glucose and glycogen are unavailable?

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Synthesis of palmitate — Fat Palmitic acid is one of the most prevalent fatty acids occurring in the oils and fats of animals; it also occurs naturally in palm oil. It is generated through the addition of an acetyl group to multiple malonyl groups connected by single bonds between carbons. This structure forms a saturated acid—a major component of solid glycerides.

When glucose and glycogen stores are unavailable during prolonged fasting, the liver adapts to provide alternative energy sources for the body.

As insulin levels decrease and glucagon levels rise, the rate of lipolysis increases, mobilizing fatty acids from adipose tissue into the bloodstream. The liver then converts a large proportion of these circulating fatty acids into ketone bodies (specifically beta-hydroxybutyric acid and acetoacetic acid).1

This process is stimulated by glucagon and serves a critical survival function: these ketone bodies are released into the blood to be used as a primary fuel source by the brain and other tissues. By utilizing these keto acids, the body substantially reduces its reliance on glucose production and gluconeogenesis, which in turn spares muscle tissue from being broken down for energy.1