Again, just talking about experience and general reading, and in no way a learned person on this topic.

There is science, medical science, experience, folk wisdom, and folklore.

There is the profit motive.

People are complicated. So complicated that what works for one person does not work for another. And the power of the mind is great enough to make a difference in how the body reacts. Short term AND long term.

I'll never forget a popular entertainer who I thought of as a lightweight doing a show on exercise, which did no harm but had one great observation at the end: "People ask what is the best exercise...the answer remains: THE ONE THAT YOU WILL DO!"

a LOT of this goes for diet. It should have enough science and medical context to fulfill that basic rule we can't get around: You must burn off more calories than you take in. And it needs to be doable FOR YOU. And there needs to be a long term life plan so that it will be effective after the weight loss. Many people are healthier and happier even if they are overweight, because they are at a stable point and they can function.

Very few of us start wise. Most of us are hammered into some form of wisdom through life experience. We learn what works and is right for us.