How do I overcome my insecurity? ?

It sounds like you're doing some healthy things for yourself, things that bring self respect. That's good. But you only mentioned physical things. Good personality traits and spirituality are more important. The Bible says that physical training is beneficial for a little, but godly devotion is beneficial for all things, as it holds promise of the life now and the life that is to come (1 Timothy 4:8). This life is temporary, with a lot of badness going on. It's God's purpose to remove the wicked and allow the meek or humble to inherit the earth (Psalm 37:29, Matthew 5:5). To learn more see JW.org.

I'm a biologist with experience in biochemistry, metabolism, cancer biology and immunology. All desire for food increases when you exercise. You exercise too much, the shift in homeostasis will make you fatigued and hungry. The DOMS stress will increase your craving for sweets etc.

Long term chronic overexercising will lead to increased risk of cancer, heart disease and other metabolic diseases. 

Yoga and other post exercise activities such as ice-baths, Saunas, jacuzzi, massage etc help counter exercise stress, but only to a point. 

Central to healthy living isn't exercise but diet calorie control and diet composition control. Successful control of diet leads to strong metabolic health. That is a better plan for strong mental performance and long a longer life. 

Reduced amount of high fat,  high sugar content food is vital because too much organ fat leads to a chronically active innate immune system, and that's what promotes cancer and CVD. 

This feeling mainly stems from a childhood program of "I'm not good enough" which is a very common core belief many people have in society. This belief was formed early on in your childhood (before age 7) due to messages you bought into from your parents, teachers, friends and other influencers. I would recommend that you seek counseling for this so you can be held accountable for learning to change and to repeat new messages of "I'm worthy" in order to re-program your brain.