Body and Mind are generally perceived as separate entities but they are not. I won’t say that they are related to each other because that will be like saying a partial truth. Deep down body and mind are one phenomenon. They are one entity at the energy level. So they are not different, they are not related but one entity.
The body is the physical part which is visible to us. The mind is the subtle and the invisible part. Any change in the body is also reflected in our mind and similarly, any change in our mind makes a corresponding effect on the body. E.g. Whenever you are sad, then laugh for some minutes and see how your emotions and thoughts change for better. Similarly feel confident from within and see how your body language changes. The people who are expert in reading body language judge the emotional state of the person by looking at the person body language. E.g. If you are confident then it will be reflected in your body language.
In spiritual dimension, the effect of breathing on your emotional state is known for thousand of years. Your breathing pattern is different for emotions of love, hatred, anger, sadness or joy. So one of the easiest ways to change your emotions is to change your breathing pattern. Whenever you feel calm and content then your breathing is harmonious and deep. You can even use strong exhalation to throw out some emotions from your system. E.g. Whenever you are feeling angry or sad or experiencing any negative emotions. Then while exhaling the breath, feel (or visualize) that these emotions are going out from you. Do the exhalation strongly for few minutes and you will notice the difference in your emotional state.
In Tibet, one of the tests of advanced meditators was to generate heat in their body in ice cold conditions. So the meditator has to sit down in ice cold conditions and by his visualization or meditation practice produce sweat in his body. So with the power of your mind or your thoughts, you make the difference to your body and vice versa.
So if you want to have a healthy body-mind then take care of what you eat, what you think and how you act. Because if you eat sattvic food then your mind will also be calm and peaceful. On the other hand, if you eat tamasic food then it will lead to lethargy not only in your body but also in your thoughts. Eating non-vegetarian food is not ideal for spiritual practice and can lead to emotions of anger, competition, revenge etc in you.