What nutrient is used to form ketones?

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The nutrient used to form ketones is fat. Here's a step-by-step explanation:

1. When the body's glucose reserves run low, the body starts to break down stored fat for energy. This process is called lipolysis.

2. During lipolysis, the liver breaks down fatty acids into a byproduct called acetyl-CoA.

3. Normally, acetyl-CoA is further broken down in the citric acid cycle (also known as the Krebs cycle) to produce energy. But when the body is in a state of fasting or carbohydrate restriction (such as in a ketogenic diet), the citric acid cycle can't keep up with the amount of acetyl-CoA being produced.

4. The excess acetyl-CoA is then converted into ketone bodies, a type of molecule that can be used by most tissues in the body as an alternative energy source. This process is called ketogenesis.

So, in summary, fat is the nutrient used to form ketones in the body.