I suspect that genetics is they key factor in weight gain. Some people thrive on Adkins-type high-protein diets due to their genetics; others need more carbohydrate. Protein and fat are my "natural" best foods; others, with different DNA, may have other dietary requirements.
There is no such thing as a one-size-fits-all healthy diet.The only safe way to determine one's proper diet is by working with one's doctor.
I have no doubt that genetics plays some role in weight gain, the way bodies assimilate food, and so forth. But I also think the "genetics" argument is grossly overemphasized, and often gives obese people a convenient excuse not to attack the problem. Most fat people, it has been my experience, blame their condition on heredity and genetics. Excuse me, but I say hogwash. Next time you're in a grocery store, find a really fat person, and take a discreet peek into his or her shopping cart. You'll usually see few (if any) fresh fruits and vegetables (some seem to not know where the produce department is); whole grain products; or skim milk or fat-free dairy products. What will you see? Almost always those giant 3 liter bottles of soft drinks (sometimes sugared, sometimes "diet"; it seems that switching to Diet Coke is regarded as a panacea); white bread; potato chips or nacho chips; butter or margarine; whole milk and ice cream; and above all, "convenience foods" -- frozen, jarred, or canned, always full of fat, salt, and sugar.
For 99%+ of the population, I am convinced, weight is determined by calories in and calories burned. And certainly you can bring your "calories in" substantially below your "calories burned" on all manners of unbalanced diets. I'd be concerned, however, about the long-term effects, especially if your diet is grossly unbalanced for an extended period of time.
I hope whatever you're doing continues to serve you well.