First of all, see an endocrinologist. If you have everything in order with the hormonal level, then to any fitness trainer, who at least should show a decent result himself. But the best indicator of his literacy will be the results of his clients.
First of all, to the literate. How to distinguish them from the rest? And nobody knows that. First you need to delve into the question yourself, read or look at different points of view. The less you know, the more noodles they will hang for you.
And now there are fitness trainers, nutritionists, weight-lifters, athletes and others a dime a dozen