What to avoid If you're going to stray from this list, there are a few things you should keep in mind. Be sure to avoid fatty foods before working out—fat leaves the stomach very slowly, which means you’ll feel full and sluggish and could cramp up easily. Although carbohydrates are good, you should not get them from raw sugar or candy. Either of those foods will cause a sugar rush and probably a crash while you’re mid-workout. Also, don’t overeat before you workout. These are all snack—not meal—suggestions. Eating too much can cause indigestion, sluggishness, nausea and vomiting.