The key is basically just to avoid simple carbs...
It's not just a matter of calories. It's all about blood sugar. The sugars in your blood are what your body runs on. And if your blood has more sugar in it than your body needs for energy, that is when it releases insulin, which locks the excess energy up in fat cells.
So again, it's not just a matter of calories. Certain foods take longer to break down into a form that your body can process than others. Carbohydrates are easy for your body to process into energy, and thus they enter the bloodstream as sugars that your cells can use for energy very quickly. Meats, veggies, and fats, on the other hand, take MUCH longer for your body to process. Proteins and fats must be broken down in the liver in a lengthy process called ketogenesis before they can be used for energy. So while simple carbs raise your blood sugar very quickly, proteins and complex carbs raise it much more slowly over a longer period of time. And since you only put on excess fat when your blood contains more energy than your body needs, it's really only carbs that cause you to gain weight, because they're the only food that raises your blood sugar enough to force your body to store it as fat.
So basically, just go for a diet with as few simple carbs as possible... no wheat, corn, rice, pasta, grains, sugar, or potatoes, and you should have no trouble whatsoever not only avoiding weight gain, but dropping weight like crazy.
Look up either the "paleo" diet or the "slow-carb" diet. I've been on these diets for 6 months now, and have lost 45 lbs, despite having to fight against the metabolic slow-down that happens with HRT. And this is with a LOT of cheating involved. (I can't help it. Sushi and pizza are too damned tempting sometimes. :p)
(And before you go saying "OMG, what about cholesterol?" I have been eating bacon, eggs, as much red meat as I want, coconut oil, fish oil, and cooking just about everything in butter, and my total cholesterol has actually dropped by 30 points, from 139 to 109. And yes, there is research that shows that low-carb diets improve cholesterol long-term. And that using natural fat sources like virgin oils and butter rather than processed vegetable oils like corn oil, canola oil, and especially anything with trans fat, is actually MUCH better for your cholesterol levels.)