Here are brief descriptions of pre- and post-workout nutrition. Keep in mind that these are only general guidelines, and not intended to substitute for the personalized advice of your trainer or doctor. Some people find they have better workouts on an empty stomach, while others lose more weight when they skip breakfast. In short, the best thing to do is to work with your trainer, figure out what works best for you, and then do it. :)
GENERAL PRE-WORKOUT NUTRITION
Eat a breakfast containing complex carbs (oatmeal is the most obvious choice). Eat whole foods no sooner than one hour prior to workout. Drink water throughout the day, not just when you’re working out. And when you are going to be working out, drink your water 1-2 hours beforehand.
Avoid greasy or salty foods (especially snack foods) prior to working out. Avoid foods that are not familiar or that are “heavy” or highly acidic, like Asian or Indian cuisine, or Italian cuisine with tomato sauce. Avoid foods that cause gas like broccoli, beans, or coffee. Processed sugars like high-fructose corn syrup can create upset stomach or heartburn because your body processes them very slowly and they sit in your stomach, sloshing around during exercise. Avoid them in general.
As long as you have consumed a carb-containing meal earlier in the day, low-carb or carb-free protein beverages can be consumed in moderate quantities no less than 45 minutes before your workout. Otherwise, working out without carbs in your system may limit energy levels.
GENERAL POST-WORKOUT NUTRITION
Generally, "post-workout nutrition" refers to foods, beverages, and nutritional supplements that are specifically consumed to help the body recover after a workout. They are only useful if your workout is strenuous enough to deplete your body tissues of nutrients. If you didn't perspire or breath heavily during your workout, or if you didn't feel a sense of muscular exhaustion afterward, feel free to pursue your normal healthy food choices.
Drink water or a moderate amount of sports drink. A protein drink with carbohydrates in a ratio of 1 part protein to 4 parts carbs has been shown to assist in providing optimum post-workout conditions to stimulate muscle growth. Chocolate milk or chocolate soy-milk are ideal in this capacity. However, if your protein intake throughout the rest of the day is adequate, there is no need to consume excess protein after your workout. Excess calories from protein can be stored as bodyfat.
For a post-workout meal, eating healthy whole foods such as bananas, nuts, whole wheat bread or pasta, peanut butter, brown rice, leafy greens and other veggies, beans, legumes, tofu, and anything rich in lean protein and fiber as part of an overall healthy diet can contribute to further calorie-burning, since protein- and fiber-rich foods take longer to digest and digestion itself burns calories (the thermic effect), among many other health benefits (Source: Nutrition for Healthy Living, 3rd Ed., Wendy Schiff).
Avoid excess sodium, grease, and processed sugars. Limit processed carbs (snack foods) at night, and avoid eating closer than an hour before bedtime. This is to maintain sleep quality.
When in doubt, ask trainer for help. One less excuse! Go work out!!!