When you want to lose fat do you use high-calorie or low-calorie foods?

When you want to lose fat, the most important thing to do is to add a period of moderate exercise to your daily routine. Moderate exercise is more likely to burn fat than intense exercise, which tends to exhaust the body of carbohydrates instead.

As for whether or not to eat calorie-dense foods, that's a personal preference. What matters isn't the number of calories in a given food, but the number of calories taken in overall. If you expend more calories than you take in, you will lose weight; how quickly that happens depends on how large that differential is.

Of course, one advantage to low-calorie foods is that they tend to be bulky and high in fiber; this can trick your hypothalamus into believing that you've eaten more than you have, making it easier to stick to a lower-calorie diet plan.