Personally, I take supplements because I know I am iron deficient, and it helps me maintain the level of nutrients I know I require in a day... because I recognize my diet isn't always awesome (though it is definitely getting better!) My go-to right now is Carnatian Instant Breakfast, because it's chocolate(ish) and I can drink it fast. It's actually encouraged me to start eating in the morning, as well as providing my iron and other needs in a much more effective way for me.
I've seen, heard of, and learned about a lot of different ways to build muscle, lose fat, and all that jazz. I've also seen doctors change their tune over the decades, I've seen the inception of BMI into our culture (which I wholeheartedly disagree with), and I've heard about very, very many different kinds of diet and "weight" loss exercises.
My advice? Learn about YOUR body. What does it respond to? Do you prefer strength training, but see huge results (the kind that you want) from cardio? Is there a way you can enjoy both, or combine the two? What sorts of foods make you feel best, and what sorts do you feel you need more of?
The science around these things is constantly changing, and it's difficult to get a handle on what is "the best" because it can be the best for one person, and for another it could be the absolute worst... and for most, it's somewhere along the spectrum.