Whether you train like an Olympian, or just noodle around once a week, the things you put into your body can strongly affect how well you fence.
Let's take a quick look at three things that sources say can help:
Protein--protein has probably been associated with physical activities longer than any other substance. Most obviously, protein helps build muscles, which are made out of protein. While building muscle isn't the thing that comes to mind first when one thinks of swordsmanship, muscles are unquestionably involved. Consuming protein after working out gives the body materials to help rebuild the muscle, as well as connective tissues, and speed recovery time.
There are plenty of way to get more protein into your diet. Protein powders & supplement are easy to find in health food stores, and offer protein from various sources that are generally easily digested and rapidly assimilated. Whey protein comes from milk and is the most rapidly assimilated. Soy is also popular, for people who don't do well with dairy. Some proteins, like casein (also a dairy derivative), are more slowly absorbed, and popular with weight-lifters who want to consume a protein that offers their muscles a slower, more continuous supply.
Protein bars are convenient ways to get protein, but be careful--some of them have a lot of calories!
Low-fat cottage cheese is considered to be a good dietary source for dairy protein.
Meat is, of course, a very traditional source of protein. Unfortunately, meat often also includes a lot of fat/cholesterol and salt, which are less than ideal, particularly red meat. Another important consideration is that meat is digested rather slowly and can slow your whole metabolism down. Avoid consuming large quantities of red meat the day before a competition or serious training session. It can make you feel like you're made of lead. Save the barbecue for the day after.
Chicken and fish are usually lighter and healthier, and more easily digested depending on how they're cooked.
The more active you are, the more protein you may need. However, too much protein can increase nitrogen in the blood which damages the kidneys. For average people, sources say you should have a hunk of protein no bigger than your fist (which is a charmingly unscientific, and not terribly useful, definition).
Do some research, and experiment to see what works best for you. You might find your muscles recovering faster when you begin to increase your protein intake. Remember to avoid sources that will also increase fat & salt. Take as much as you feel you need to help your recovery, but you won't need much extra, since "bulking up" isn't your goal, and too much at one time will not be absorbed.
Carbohydrates-- "Carbs" are the fuel your body actually runs on. After you burn through the carbs in your blood stream, you body begins to break down muscles into "burnable" compounds, and if it still needs more, it will then metabolize your body fat into fuel. (Your fat is like your body's savings account, it will break down and "spend" muscles before it goes for the fat reserves. This is why some people who exercise for weight-loss don't loose much weight: their body is reserving the fat for an emergency!).
Supplementing with carbs before you exercise can give you more energy to run on. If you've found yourself running out of steam before you're done, or you just can't find the energy you need to get up to speed when you train, you may benefit from increasing carbs before you start. Be careful, though! The unused carbs you consumed will be converted to fat and stored for future use.
As with proteins, some sources for carbs are better than others. Simple carbs are usually starches and are easily metabolized, while complex carbs, like sugars, take a lot more work for your body (in the form of an insulin release) to metabolize. You can find simple carb supplements in stores, or you can use dietary ones, like pasta, or starchy vegetables. You can consume them a couple of hours before training. Highly conditioned individuals facing an extended competition might even "carb load" which is to say, consume a lot of carbs the night before a competition to saturate their bloodstream with usable fuel. Any carbohydrate that isn't utilized gets converted to fat, so don't overdo it!
Hydration-- Experts say that almost all people in industrialized societies are going around in a state of mild dehydration! Dehydration will make you uncomfortable, it can make you confused or even become overheated. You body needs plenty of fluids for the chemical exchanges going on inside your muscles: bringing carbs into the muscle and taking waste materials and heat out. Hydration is vitally important for strong exercise. Always try to drink 16 ounces of water or a sports drink before working out to keep you well hydrated.
Water is great for hydration. Sports drinks frequently include mild mineral salts, or "electrolytes," to replace substances your body may be metabolizing or sweating out. These minerals are considered to help your nervous system work properly. Avoid sugary beverages for hydration! The sugar can actually make you more thirsty, and the sugar also causes your body to release a burst of insulin to break down the sugar, and that can also cause your energy level to drop fast.
So, in a nutshell consider:
Carbohydrates before practice
Protein after practice
Hydration before and during practice.
I have not found a single, ideal source in book or on the web to recommend for specific amounts, since everybody is different, and it depends on your level of training. The best thing is to do your own research to start, then experiment --slowly and sensibly-- to find out what improves your performance.
Looking forward to your feedback!