Shocking Simulation Reveals What Happens To Your Body During A 7-Day Fast

If you’re thinking about giving a seven-day fasting challenge a shot, you might want to see this simulation first. It breaks things down in a way that could make you rethink the whole plan.

Fad diets have been around forever. But some of them really push the limits of what’s healthy or even manageable.

From intermittent fasting styles like the 18:6 method to the popular 5:2 approach, there are all kinds of eating patterns people try to stick to these days.

There's also the 'One Meal A Day' (OMAD) trend, which some folks swear by. But like anything extreme, it definitely comes with some risks you should think through first.

Still, compared to those, doing a full seven-day fast is in a league of its own when it comes to how intense it is.

Long before people were using Wegovy and similar meds for weight loss, fasting was already being used as a go-to method to drop pounds or detox.

Fasting for seven days causes the body to rapidly change Getty Stock Image

There was already a simulator that showed what happens to your body when you go without food for 36 hours. Now, there’s a new one that takes it a step further and shows what a full seven-day fast does.

The video comes from the YouTube channel @Health_and_Fitness-w7g. It walks viewers through the whole process—step by step including what’s happening inside your body, the possible benefits, and the risks that come with it.

At one point, the video explains: "After one to two days, all carbohydrates from your last meals are digested, and the body uses them as its last fuel."

At that point in the fast, the video says “the hunger hormone, ghrelin, will rise and you will start to feel hungry” because your body is running low on fuel, and your calorie intake is basically at zero.

The simulation also notes that after about two or three days, your pituitary gland will begin increasing growth hormone production. This helps slow down muscle loss more than most people would expect.

It changes what energy we use Getty Stock Image

By the third or fourth day, your glycogen stores your body's quick-access energy stash—are just about gone. At this point, your system shifts gears and starts burning fat instead of sugar for energy.

This is also when something called autophagy kicks in, which is a natural process where the body clears out damaged cells and proteins.

Between day four and five, autophagy might even start targeting harmful or abnormal cells, including some linked to cancer. That’s part of why this stage gets so much attention from fasting enthusiasts.

Around this time, you might notice some surprising upsides.

People often report better mental clarity, improved memory, and a more focused mind once the body is fully into the fasted state.

Between days five and seven, your body enters what some call the 'true healing' phase, thanks largely to the effects of autophagy doing its deep cleaning work.

This cleansing process reaches its highest point here, but your body starts hitting a wall. Muscles can no longer maintain themselves without food, and muscle loss becomes more noticeable and concerning.

For most people who try fasting, the goal is to reach that autophagy phase where the body starts its self-repair cycle. And interestingly, autophagy can actually begin as early as 18 hours into a fast.

You might be wondering how anyone manages to fast this long, but it turns out there are a few things you can still consume that technically don’t break the fast.

For example, drinking herbal teas, plain black coffee, or water is typically allowed—as long as you don’t add milk, sugar, or anything extra to it.

These drinks can help keep you feeling a little more energized and might even take the edge off your hunger while still keeping your body in a fasting state.

Of course, it’s always smart to talk to a doctor before making any major dietary changes. And definitely stop if you start feeling unwell at any point.