calorie restriction can cause a reduction in resting metabolic rate through "metabolic adaptation". that is, your body gets used to the deficit (by shedding metabolically active tissue and other things*) and burns less calories at rest. so, paradoxically, restricting or reducing your caloric intake can have no effect whatsoever on your weight.

see: https://pmc.ncbi.nlm.nih.gov/articles/PMC9036397/