The thing that is so frustrating about videos like the one below is that they assume that the only way to lose weight is to "drastically reduce calories while simultaneously drastically increasing exercise". This way of thinking is based on the traditional "calories in vs calories out" model, that has been proven time and time again to be factually inaccurate.
When you only study a single group of people who embarked on the same journey, you're going to find similar results, namely the "slowed metabolism" they mention in the video. However, if you look at studies of people who have made gradual lifestyle changes that involve making healthier food choices (not necessarily slashing calories, sometimes actually increasing calories) while incorporating exercise you find that there is no negative effect on the metabolism, in fact it's the opposite. You find that the body works the way it's supposed to because it's getting the fuel it needs to handle the output that's being asked of it.
Bottom line, the thing to shoot for is gradual, sustainable changes that allow your body to adjust to what's going on so that it can be maintained indefinitely.
That is the road to health.
Just ask some of our success stories like Greg, Hannah, Raul and Wendy (and many others).
Follow the whole story here