Most diets tell you what to eat. Intermittent fasting, or IF, is different. It's an eating pattern that focuses on when you eat. Instead of grazing throughout the day, you cycle between periods of eating and periods of voluntary fasting.

This isn't a new fad. For much of human history, people ate this way out of necessity. Food wasn't always available 24/7. Fasting has also been a part of spiritual and religious practices for thousands of years, from Ramadan to Lent. Today, people are exploring it as a structured approach to health.

When you eat, your body is in the “fed state.” It spends several hours digesting and absorbing food. During this time, your insulin levels are high, and your body uses glucose from your meal for immediate energy. It's difficult for your body to burn fat when insulin is high.

After about 12 hours without food, your body enters the “fasted state.” With no incoming food energy, insulin levels drop. Your body then starts to tap into its stored energy reserves, primarily body fat, for fuel. Intermittent fasting is simply a way to extend the time your body spends in this fat-burning state.

There's no single way to do intermittent fasting. The best method depends on your lifestyle and preferences. Here are a few of the most popular approaches.

Each of these methods creates a regular pattern of fasting that allows your body to shift its energy source. The key is consistency, whichever pattern you choose.

Now that you understand the basic concept and the different approaches, let's test your knowledge.