YouTube challenges have been around for almost as long as the platform itself. Some, like the ALS Ice Bucket Challenge, are a force for good. Others, however, can be unusual or even dangerous, like the Cinnamon Challenge or the now-infamous Tide Pod Challenge. One challenge in particular became famous in the wake of Olympic swimmer Michael Phelps revealing the sheer volume of food he eats while in training: The 10,000 Calorie Challenge.

True to its name, people who do the 10,000 Calorie Challenge must consume 10,000 calories of food in one day, just like Phelps and other athletes who often consume this much to keep up with their metabolic needs. While Phelps came out recently to admit his alleged 12,000-calorie diet was an exaggeration, the spirit of the claim still rings true. Athletes need a ton of calories to do what they do, and 10,000 in one day is not entirely unheard of.

But what about us regular people? What would eating 10,000 calories in a day do to someone who isn’t spending upwards of six hours a day performing high-intensity exercise? What would happen to an average human body on the Michael Phelps Diet?

What’s the deal with calories, anyway?

First, let’s go back to Health 101 and talk about calories. Calories aren’t a “thing,” but a unit of measurement. One kilocalorie, or “food calorie,” is the amount of heat needed to raise the temperature of one kilogram of water by one degree Celsius. One gram of protein or carbohydrates provides about 4 calories, while one gram of fat provides about 9. Our bodies use this heat as fuel to help them function normally. We cannot survive without the energy provided by calories in food.

Consuming more calories than we burn off in our daily activities can lead to weight gain. Experts estimate that it takes about 3,500 excess calories to gain one pound. Conversely, creating a calorie deficit–burning more calories than are consumed–can lead to weight loss. Losing 1-2 pounds per week is considered healthy and sustainable.

If you consumed 10,000 calories in one day, you would need to expend 10,000 calories worth of energy to break even, or at least 13,500 calories if your goal is weight loss.

For context, a 155-pound person would have to do a high-intensity workout (swimming, running, etc.) for nearly 15 hours to burn off all those calories!

Is the 10,000 Calorie Challenge dangerous?

No reasonable person could recommend anyone eat 10,000 calories every day for any regular period of time. Unless you are looking for significant weight gain, or your profession involves hours of strenuous physical work–like a professional Olympic swimmer, perhaps–a daily diet of 10,000 calories could spell certain disaster for your body as it tries to keep up with all the fuel you’re feeding it.

Michael Phelps and other athletes can sustain a diet of this nature because of the intensity of their training. In his prime, Phelps explained that he trained at least five hours a day six days a week. That’s almost a full-time job’s worth of exercise! Most of us probably don’t even have the time to make and eat 10,000 calories worth of food every day! Let alone spend hours upon hours burning it all off again.

It’s also worth noting that most of the YouTubers completing this challenge specifically choose high-calorie foods regardless of their nutritional value. All that junk food can be devastating for your health if eaten regularly.

That said, doing the 10,000 Calorie Challenge just once will likely not make or break you. You will most certainly feel sick the next day, though. We wouldn’t recommend trying it, but if you’re going to, be sure to buy antacids!

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