Sally!
You are already on a great path to recovery. Being active, which you are, is the first step. Yoga is "fantastic" for you and I highly recommend it and do it several times a week. It promotes both stretching and resistance as well as a calming effect which helps regulate your cortisol levels by helping lower stress.
Muscle doesn't "convert" to fat, in fact lean muscle mass will burn adipose tissue (body fat) for energy. The more lean muscle mass that you "build" the more calories you burn while at rest. If your body has the necessary components and the right conditions to promote protein synthesis (the "anabolic" process your body triggers to turn amino acids into lean body mass) you will build muscle.
So exercise, like walking and yoga, resistance training etc...starts the process of building muscle by actually tearing down muscles which tells the body it needs to repair them, the more damage the stronger your body will rebuild them if given the right tools for the job so to speak.
Now the right tools for the job of protein synthesis are these, an androgen (testosterone), building blocks like amino acids (proteins), and fats (all cell walls need lipids/fats), water, and the energy to build them. All of the macro nutrients, fats, proteins, carbs, can be broken down into energy, or "metabolized".
There are two different metabolic pathways (ways to process energy in the body) and they are the "Anabolic" and "Catabolic".
Catabolism (Greek kata = downward + ballein = to throw) is the set of metabolic pathways that break down molecules into smaller units and release energy. In catabolism, large molecules such as polysaccharides, lipids, nucleic acids and proteins are broken down into smaller units such as monosaccharides, fatty acids, nucleotides, and amino acids, respectively. As molecules such as polysaccharides, proteins, and nucleic acids are made from long chains of these small monomer units (mono = one + mer = part), the large molecules are called polymers (poly = many).
Cells use the monomers released from breaking down polymers to either construct new polymer molecules, or degrade the monomers further to simple waste products, releasing energy. Cellular wastes include lactic acid, acetic acid, carbon dioxide, ammonia, and urea. The creation of these wastes is usually an oxidation process involving a release of chemical free energy, some of which is lost as heat, but the rest of which is used to drive the synthesis of adenosine triphosphate (ATP). This molecule acts as a way for the cell to transfer the energy released by catabolism to the energy-requiring reactions that make up anabolism. Catabolism therefore provides the chemical energy necessary for the maintenance and growth of cells. Examples of catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use amino acids as substrates for gluconeogenesis and breakdown of fat in adipose tissue to fatty acids.
There are many signals that control catabolism. Most of the known signals are hormones and the molecules involved in metabolism itself. Endocrinologists have traditionally classified many of the hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The so-called classic catabolic hormones known since the early 20th century are cortisol, glucagon, and adrenaline (and other catecholamines). In recent decades, many more hormones with at least some catabolic effects have been discovered, including cytokines, orexin (also known as hypocretin), and melatonin.
Anabolism (from Greek ana, "upward", and ballein, "to throw") is the set of metabolic pathways that construct molecules from smaller units. These reactions require energy. One way of categorizing metabolic processes, whether at the cellular, organ or organism level is as 'anabolic' or as 'catabolic', which is the opposite. Anabolism is powered by catabolism, where large molecules are broken down into smaller parts and then used up in respiration. Many anabolic processes are powered by adenosine triphosphate (ATP).
Anabolic processes tend toward "building up" organs and tissues. These processes produce growth and differentiation of cells and increase in body size, a process that involves synthesis of complex molecules (protein synthesis). Examples of anabolic processes include the growth and mineralization of bone and increases in muscle mass.
Now the key here is to set your body up, through nutrition, to be in an anabolic state which you can do by giving your body the triggers it needs to start the anabolic process of protein synthesis. Protein synthesis requires testosterone (which can be promoted in your body by the percentage of fat in your diet, and in men by promoting the production of LH (Luetinizing Hormone) in their system. LH being what the testicles convert into testosterone. Women produce 1/7-1/8th the amount of testosterone than men and that's done by the ovaries) and Leucine, the branched chain amino acid found to be the trigger for protein synthesis, which is found in protein.
SO in short, up your good fats(poly and monounsaturated fats with a good ratio of omega3 to omega 6's) to promote testosterone production, get good amounts of protein, maybe even supplement Lucien by taking a BCA (branched chain amino acid) supplement, lower cortisol levels (stress), control insulin by not spiking blood sugar levels with simple carbs, and be active.
Sex, with someone else or solo, helps promote healthy hormone production. If you have no sex drive, try to jump start the engine by whatever means you can.
