Let me just briefly point out some things which are perhaps so obvious that they often get overlooked.
First of all, the genetic contribution to your body weight found from twin studies seems to be around 80%. This makes body weight one of the most strongly genetically correlated traits there is. That doesn’t mean you can’t change it… just that it will be hard.
Second of all, different populations of people around the world have very different inherited abilities to digest food. Sami people in the arctic generally never lose their ability to digest milk, while other populations lose it just after infancy. Some of the fastest developments in human genetics in the last few millennia have been an ever widening of people’s abilities to digest a variety of foods.
My point is that there is NOT one ‘universal diet’ that is good for everyone and it is likely that there never will be. Take all the studies and correlations with many grains of salt because the people being tested may not be like you. Think of them as advice, try things out, and most of all listen closely to what your own body is telling you about whether the advice is good advice for you.
In the same wise, there really is no point arguing with someone else that your diet which works great for you should of course work for them, or vice versa that someone else’s diet which is working great for them cannot possibly be doing so. Human bodies are absurdly complex. If someone found something that works, give them a big high-five! Yay!