The question of whether you should eat before speaking is very individual. Some people want to eat – others do not. By the way, you are not alone in this dilemma. Most professional athletes, stage actors, and musicians do not eat a large meal before performing.
There have certainly been times in the past when I've been teaching a private session on an empty stomach and my stomach started to growl. In a situation like this, it is a good idea to have some type of snack food available like a granola bar or some fruit that you can nibble on; however, when it comes to the speech or presentation, chomping on an apple is not in the picture.
The real question is the big presentation in front of the microphone or standing at the head of the boardroom table. Good microphones today can pick up a lot of sound, especially in close range. On the other hand, if you are at the head of the boardroom table, those sitting to your immediate left and right will hear every sound your body makes.
You should definitely have something in your stomach so that it does not growl during your performance; however, the last thing you want is too much in there. Feeling full is not good when your nervousness is at its height. If you feel like you could unbutton the top button of your trousers, pants or skirt or need to unloosen your belt, you definitely overdid it.
Remember, too much food in the stomach can produce undesired audio results as well as too little!
Eating a few hours before you speak is ideal. But what happens when you are the after-dinner speaker and they have the place of honor for you in the center of the dais?
Do Not Drink Alcohol.
While you may think that you can handle a drink before speaking or that it may help to relax you, I beg to differ. When you drink, you lose your edge. The last thing you want in public speaking is feeling too relaxed. You need to be sharp, clear, crystallized. Alcohol allows for none of that. It dulls the senses. So stay away from liquor. Instead, drink water, coffee, tea or juice. Avoid milk products as well because they create extra phlegm. Excessive clearing of the throat while speaking is annoying and hard on your vocal folds (cords) as well.
The best advice I can give is to use common sense in your choice of foods; have something in your stomach so that you are not starving; and save your dessert for afterwards.