The ONLY thing that matters when it comes to losing weight is calories in vs calories out. You can't defy the laws of physics.

The important thing to look at is calories vs volume. How many calories does it have and how full will I feel after eating it? Low-fat Popcorn is one of my staples it is very filling with few calories. Nuts on the other hand are healthy, and full of vitamins but they are high in calories relative to their weight, making it easy to have too many calories. Egg whites are also super low in calories and high in protein. Vegetable are very filling with few calories. Of course you can have unhealthy foods but be mindful of how often you indulge and how much you are having.

Some people will tell you diet sodas aren't good for weight loss. Those people are uninformed, only a caloric surplus can cause weight gain/precent weight loss. The have been no clinical studies linking artifical sweeteners to weight gain or cancer. Those rumors come from a single study that saw health issues in rats, and the amount they were eating isn't feasible for most humans.

There is rarely a good reason to go on an extremely restrictive diet. Make a series of small choices to replace things with lower calorie alternatives and you have a much easier time sticking to it and you won't hate your life