I am not overweight and not a specialist for diets. However, recently I read one book about nutrition that made a big impression on me: The China Study by Colin Campbell. It doesn't give you a specific diet plan, except for the recommendation to avoid all animal proteins. But if that sounds hard, the book provides ample motivation, because it summarizes lots and lots of studies that show that most "civilization diseases", like heart disease, cancer, multiple sclerosis, diabetes and more can be avoided by such a diet. But the author is not a crank or self-announced health guru, but a scientist who has devoted his life to studying these things. The most extensive study is the China Study that gave the book it's name, but it is not the only one.

As for losing weight, I remember that he writes that people with a mostly plant based diet tend to actually eat more calories than meat eaters, but stay slimmer nevertheless - the energy is used in a different way. He also criticizes some popular diets, for example while Atkins dieters lost weight in studies, what is less known is that they also lost critical amounts of calcium. Overall, Atkins is apparently very unhealthy.

Also, apparently people who switch to plants based diets also lose weight, without calories counting.

Of course I am not a health scientist, so I can't judge the book. But it sounded convincing to me, also because even before I read it I had a feeling I should try to avoid dairy products. I did some google searches but found no refutations of The China Study (it has a section on the grip of the food industry on the dieting market).

In fact, I would be interested in hearing other people's opinions.