What are ketones?
Ketones are a backup fuel your liver makes from fat when sugar is scarce, for example during fasting or a very low-carb diet; your brain and muscles can run on them.
Think of a hybrid car. Normally it runs on gasoline (sugar). When the tank runs low, it switches to the battery (ketones, made from your fat stores) and keeps going.
Why it matters for aging
When you eat regularly, your body runs mostly on sugar. After many hours without food, or on a very low-carb diet, stored sugar runs low and the liver starts turning fat into ketones. This state is called ketosis.
Ketones aren't just fuel; they also act as signals that can switch on some protective genes, which is why researchers study them in aging. Ketone levels from fasting or diet are different from diabetic ketoacidosis, a dangerous condition in people with type 1 diabetes.
A common myth
Being in ketosis burns fat magically, regardless of how much you eat.
Ketones show your body is using more fat for fuel, but fat loss still depends on overall energy balance. Ketones are a useful signal of a fasted state, not a weight-loss shortcut.
Go deeper
Deep dives
- Does intermittent fasting slow aging? What the trials say
- How long do you have to fast for autophagy? The honest answer
Related terms
Updated Nov 9, 2026 · All terms