Your body language tells others more about you than the words you say because it reflects who you are and what you are thinking without a filter. Body language is within your control, at least to some extent. Control starts with your beliefs and thoughts. When you let limiting beliefs take root in your mind and spin up negative stories for you, those beliefs affect your body language.
Limiting beliefs left unchecked will affect both your body language and your actions. You can control your body language by controlling your beliefs and being conscious of the way you hold yourself.