While intermittent fasting may share some of the qualities of a trendy diet, the fact is, it’s neither a trend nor a diet. Its inception has been attributed to as far back as prehistory where fasting was actually a survival mechanism devised during bouts of famine.

It’s not a diet because its effectiveness has a lot more to do with when you eat relative to what you eat; in this sense, intermittent fasting is a pattern of eating—a strategic way of scheduling your meals so that you get the most out of them. There are several variations to how it’s done, but the general idea is to block off a certain number of hours for eating, and fasting throughout the remaining time, during which your body undergoes certain changes. This is what happens to your body during intermittent fasting:

It starts with the liver

The root of all intermittent fasting’s benefits has to do with what happens to our liver during meal times. When we eat, we store some of that energy in our liver as glycogen (think of this as an energy reserve), but if you choose to fast for, say, at least 10 hours, your glycogen levels will drop, causing you to feel a bit irritable. But with little glycogen left, fat cells in your body will release fats into your bloodstream. The fat cells head straight to your liver, where they’re converted to energy for your body and brain. What’s happening here is that rather than using up the little glycogen you have left in order to synthesize energy for your body and brain, you’re burning stored fat instead—so you are literally burning fat to survive.

What happens to the brain

Once you’re in that process of burning stored fat, what happens next is you release chemicals called ketones. These chemicals help build and strengthen neurons and neural connections in areas of the brain responsible for learning and memory. Intermittent fasting (or periodically restricting calories) signals the brain to create protective proteins that strengthens its connections, thus improving cognitive function and promoting the growth of new brain cells.

Though intermittent fasting isn’t the only way to increase ketone production. The same logic more or less applies to the ketogenic diet, where increasing the production of ketones is done by incorporating more fat in your diet (and cutting back on carbs). However, it’s been shown that intermittent fasting can increase ketone levels by up to 20 times, while going on a ketogenic diet only increases ketone levels by up to four times.

It’s not a diet because its effectiveness has a lot more to do with when you eat relative to what you eat; in this sense, intermittent fasting is a pattern of eating—a strategic way of scheduling your meals so that you get the most out of them

What happens to your belly

When you have low glycogen levels, your body has no choice but to burn stored fat in order to synthesize energy. The good news is that the fat being burned includes stubborn belly fat.

What happens to your muscles

Shedding pounds leads to the loss of fat tissue and muscle, but intermittent fasting can ramp up fat burning so that you lose more fat and less muscle.

What happens to your heart

It’s hard to identify the specific effects of fasting on the heart because a lot of people who fast do it for health reasons. These people tend to not smoke, which can also reduce heart disease risk. Nonetheless, it’s been found that intermittent fasting positively affects the way you metabolize cholesterol and sugar such that levels of bad cholesterol can be decreased by up to 32 percent and triglycerides by up to 42 percent. This can reduce your risk of gaining weight and developing diabetes, which are both risk factors for heart disease.