>>76324087 (OP)build muscle, thermodynamics and cico show us that as a larger star loses its energy and decays to red dwarf faster, having more muscle will will expend more energy.
You gotta lift, start with negative pull ups if you've never done a full one, then legs, push muscles, pull muscles and cardio, start light.
For diet changes, try for foods that you chew for a while on one side. a big factor in why people get fat is the easy single crunch per item food, food producers found out it releases less sating chemicals in the brain and they generally went to the addiction model of sales.