You can teach your body that everything is ok and it's healthy and safe to use up extra calories with energy to do fun things. The first step is to remove the fear of weight gain.
The body senses danger when you restrict calories. The thyroid automatically lowers metabolism in order to conserve calories and store fat. It's a simple survival method that can get out of control and cause a variety of health problems, including weight gain.
In a healthy body, the thyroid releases T4 which is converted to T3, the active hormone. T3 is the thyroid hormone that raises body temperature, metabolism and everything from heart rate to liver function and energy. When the body senses danger or starvation, then some of the T4 is converted to Reverse T3, helping you store fat in case of emergency. Reverse T3 is inactive, so body temperature, metabolism, heart, liver and energy are lowered.
Another way to think about it, is the balance between the thyroid which regulates metabolism and the adrenals which regulate stress. When stress goes down, metabolism and thyroid go up. When the adrenals go up due to stress, the thyroid and metabolism go down to help you gain weight to deal with the stress.
So, to raise metabolism and improve liver detoxification and energy we have to tell our hormones that everything is ok and there's no risk of death or starvation. Think relaxation, sleep, play, meditation, enjoyable exercise and eating healthy, hearty meals on a regular basis. These healthy activities tell your body, adrenals and thyroid that all is good and it's ok to burn up calories as extra energy to enjoy this fabulous time of life.