When you ask if intermittent fasting (IF) works without calorie counting, it helps to specify what “works” means. If you want IF to reduce your body fat to 3 percent, it may not work, while if you want to reduce your body fat to 20 percent, it certainly can. If, by “work,” you mean “lose surplus fat,” then the answer is “sometimes,” because it depends on which IF schedule you choose and whether that schedule provides appetite correction for you. Appetite correction is the ideal approach to losing surplus fat, because once it kicks in, you’re not fighting your body by restricting your intake — it simply wants less, and tells you when you’ve had enough while taking into account surplus fat, so you still lose at a reasonable rate (an average of 1 pound per week in most cases).

I have the most experience with the 19/5 schedule of daily IF known as Fast-5, which has been around since 2005, so there’s a lot of user experience to draw on. Fast-5 provides appetite correction for most of the people who try it, so calorie counting is usually not required. There have been some people, though, who maintained the schedule consistently and did not see appetite correction until they shortened their window further, to 4 hours or even shorter. Some did not see appetite correction at any point, and still had to count calories, but continued the schedule because it was easier to stay within their calorie budget on the Fast-5 schedule than it was on a conventional three-meal-a-day (3MAD) schedule. If you’re not seeing appetite correction on your current IF schedule, or you have to count because you’re on a weekly schedule with a 600–700 calorie/day limit, trying the daily schedule with a shorter eating may work for fat loss without counting calories.

One of the things I’ve learned since 2005 is that different people respond differently to different schedules, so individual tweaking of a schedule to find the best fit that works well for you is something only you can do — when it comes to IF, one size most definitely does not fit all.