An apple day is used for naturally occurring plateaus lasting more than 4 days, and is purported to help break the stall. What is a naturally occurring plateau? This is where your weight does not move (up or down) for four days for no apparent reason, such as eating something off protocol, going through your menstrual cycle, exceptional stress or insomnia, etc. If any of these factors are present during a stall, this is not considered a naturally occurring plateau, and an apple day would not be appropriate and, in fact, could have the opposite effect.
If you are on a naturally occurring plateau, we would recommend you wait it out and stay faithful to the program (stay off the scale for a few days, take your measurements instead). Plateaus are normal and will pass. Often during a plateau, even though the scale isn’t moving, your body is changing, so you will likely see a change in measurements.
It is important to note that Dr. Simeons mentions that apple days are purely psychological – they produce a loss because apples are a natural diuretic. In our experience, apple days used in the wrong situations can have the opposite effect and we rarely recommend them.