Practice yoga on an empty stomach, so the meal will not get in your way when you twist and bend. The energy we create during the practice is ‘prana’, which is different energy than ‘apana’ that is generated by eating. Also, drink before or after the practice to cleanse your body and to hydrate. Try not to drink during the practice, because it will lower down your body temperature.
A lot of yogi’s and yogini’s are vegetarian, or vegan, or something in between. One of the ethical principles of yoga philosophy (ahimsa) is that you don’t hurt other beings (non-violence). However, adapting your food choices is never a requirement to start practicing yoga. On this place, you can find primarily information about veganism, because it happens to be that I’m vegan too! I was already vegetarian long before I started practicing yoga and I turned vegan because of my own beliefs.