Simply counting calories, and ignoring what you put in your mouth might not lead to good health.
Insulin levels will rise significantly more after consuming carbohydrates than after eating fats (no rise at all) or protein. Some carbohydrates, also known as carbs, get into the bloodstream in the form of sugar (glucose) much faster than others. Refined flour is a fast carb, while coarse oatmeal is slow. Slow-release carbs are better for body weight control and overall health than fast carbs.
A 500-calorie meal of fish/meat, salad, and some olive oil, followed by fruit, is much better for your health and will keep you from being hungry for longer than a 500-calorie snack of popcorn with butter or toffee.
There are several diets today which claim to help people lose or maintain their body weight. Some of these have been extremely successful and good for participants, but are notoriously difficult to adhere to long-term.
Medical News Today recently published an article discussing the "Eight Most Popular Diets". The rankings were based upon how many articles mentioned them favorably, how popular they were generally and which ones received the most positive feedback.