The '3 Week Diet' Says It'll Help You Lose More Than 12 Pounds

Why you should choice 3 Week Diet system:

You can get into firm third- or fourth-date territory in three weeks. You can binge watch a couple of seasons of your favorite show on Netflix. You can even break in new running shoes.

Something that's not as easy to do in 21 days? Lose a noticeable amount of weight.

Enter: The 3 Week Diet by Brian Flatt. The plan claims to help you “melt away several pounds of stubborn body fat” in 21 days, and the website offers up plenty in the way of impressive before-and-after pics.

The plan combines a lower-calorie diet with intermittent fasting, a slashed carb intake, exercise, and a supplement routine.

Flatt told Business Insider that his diet helps people know exactly what to eat, how much of it to eat, and when to eat it in order to maximize weight loss. He also shares exercises he says will burn fat quickly.

To follow the diet, people need to order the “3 Week Diet System,” which includes:

The diet's website doesn’t offer up a ton of details about how it works—you've gotta pay for that kind of intel. That's a big red flag, says Julie Upton, M.S., R.D., co-founder of nutrition website Appetite for Health.

And the news about the 3 Week Diet just gets worse from there: “Losing 12 to 23 pounds in three weeks sounds appealing but it would require a very, very low calorie intake with significant exercise to create such calorie deficits," she says. "You'd also lose a lot of muscle mass at the same time. So, the claims of melting belly fat are just bogus.”

FreeDieting.com offers a little bit more info about the diet and says that it has three phases, with phase one being the most intense.

During that time, people eat just protein and vegetables. And yeah, if you do this, you’ll lose weight, says Beth Warren, R.D., founder of Beth Warren Nutrition and author of Living a Real Life with Real Food. “The weight loss may seem more rapid because without carbohydrate stored as glycogen, you lose fluid,” she explains. “However, once you begin to eat [non-veggie] carbohydrates again, your weight will increase. Therefore, it’s not a long-term solution.”

And given that Warren says a safe amount of weight to lose is about two to three pounds per week, well, 12-plus pounds is...not that.

"Losing 23 pounds in three weeks is too fast,” Warren says, especially since people who lose weight slowly are much more likely to keep it off.