The answer depends on two factors: your overall diet and how intense your workout is. If you eat small, balanced meals every few hours while you’re awake, you don’t really need a pre-workout meal strategy. Your body should have ample fuel to get you through any workout around an hour or less (longer workouts have specific needs).
However, if you go longer than 3 hours without eating, you should determine your needs based on a few things. First, how hard is your workout? Easy aerobics and other work where your heart rate doesn’t exceed 140/150 bpm (easy yoga, slow jogging, cycling, hiking, etc.) don’t use a lot of fuel (blood sugar and its back-up, glycogen) and can be done effectively on a fairly empty tank. Good hydration (water, water, water) should be all the fuel you need.
Harder workouts have an anaerobic interval component which burns your limited stores of glycogen. Your body stores glycogen until you need it, but when your diet is very lean, you will almost certainly deplete these stores before the end of your workout if you haven’t eaten in a while. This condition, called “bonking,” causes your performance to instantaneously plummet.
Here are some options & general rules to avoid the dreaded “bonk.” Pick the one that best suits your day.
3 hours prior to a workout: Eat a well-rounded, light meal. As long as it’s not too many calories (more than 500-ish), most of it will be turned into fuel by the time you begin. Almost any of my meal plans fit this mold, as you have ample time to digest.
2 hours prior: Eat a light snack that’s mainly carbohydrates (4 parts carbs to 1 part protein with little fat will ensure there’s time to convert it into glycogen). Energy foods, like granola with yogurt and fruit, are ideal.
1 hour prior: Eat very light, no more than 200 or so calories at around a 4:1 carb to protein ratio. Low-fat, plain yogurt with a little fresh fruit thrown in is ideal. Any extra protein and fat will hinder your workout. It’s similar to the 2 hours prior snack, but since your body can only convert 200 to 300 calories into energy in a given hour you’ll want to keep the portions smaller.
Less than 1 hour: Try not to eat during the last hour before your workout. If you haven’t eaten in hours, liquid fuels, like juice, or easily digestible carbs, like half of a banana, will digest fast enough to help you during the later stages of the workout when your glycogen would otherwise run out. This is also a good time for targeting caffeine intake for ergogenic benefit.