Boxing does burn off a lot of calories. But that doesn't mean that people who are in the sport should just chuck healthy eating out of the window. Whether boxing for competition or to just get and stay in shape, eating the right things should be a top priority.
Within a two hour window before going to the gym, eat light, and eat something that will give energy. If a person is going straight from the job to the gym, this may be a challenge. However, foods like peanuts, cashews, and raisins can be kept inside the desk. Having fruit is another good idea because it's natural sugar. It will not give a person an unnatural sugar high only to crash down once it's worn off. Fruit is also easier on the digestive system.
If competing, depending on the time of day the fight takes place, plan out the meals properly. Eat a good breakfast, but go easy on the sausage and bacon, and skip the breads like pancakes and French toast. Have an omelet with vegetables, and have some fruit. If meat is involved, fish is a good idea because it is light. Bypass the fast food places at lunch time, and have salad and soup. A full dinner is not recommended, especially if the fight takes place in the evening, but light, healthy snacks will work. Be mindful of having to weigh in before the fight.
Water is the best bet for hydration, better than sports drinks, and certainly better than sodas and juices.
After the workout or after the fight, don't fill the system up with heavy foods, especially if those foods are sugary, salty, or greasy. Why put back on calories that were burned off? Follow a sensible eating plan a majority of the time, and the results will be great.