A human body doesn’t require any energy to store fat, but it does for muscle. That’s why most diets fail. Abrupt reduction in calorie intake leads to muscle and fat realignment. The IIFYM RMR Calculator is used to calculate one Resting Metabolic Rate which is very similar to ones BMR or Basal Metabolic Rate with a few differences. RMR is a very useful tool for flexible dieting with IIFYM techniques in mind.
The Person that is flexible dieting quickly loses weight, muscle and fat. When normal consumption is resumed the weight quickly rebounds because the body is now burning fewer calories to sustain itself.