The information in this article comes from my experiences, the nutritional information in Cycling Plus magazine, and advice from fellow riders on the newsgroup uk.rec.cycling.
Drinking enough is actually more important than eating. If you allow yourself to become dehydrated, your efficiency on the bike can drop dramatically. This is true no matter how fast or slow you ride. On the other hand, if you are riding slowly enough, you can ride without eating anything at all: your body can be trained to burn fat as you ride. (However, most people like to ride faster than this, so this isn't terribly useful in practice.)
The main methods of carrying water are water bottles and hydration packs. I tend to use water bottles for road rides, as I like to ride without anything on my back when I can. I tend to take two large water bottles with me when I'm out for any length of time. When I get down to only about a half a water bottle left, I'll stop and get some more water. Two large water bottles will last me anywhere between about 30 miles to 70 miles, depending on hot and humid it is.
When I ride off-road, I usually use a hydration pack (otherwise known as Camelbak, these are small backpacks with plastic bags with hoses to hold the water). There are two main reasons for this. First, water bottles end up covered with mud, and this deters me from wanting to drink from them. Second, a hydration pack holds more water than I can get in water bottles. You can fit a bit over 2 liters in your standard bladder, while the usual large water bottle holds about 0.8 liter, giving about 1.6 liters for two bottles. I find the larger capacity useful for off-road, when I'm less likely to be going through villages where I can get more water.
Energy drink is useful for a couple of reasons. First, it is a constant feeding of calories to your body, and these calories come in a form that's ready to use as is, requiring very little in the way of digestion. If you use an energy drink you can get away with eating less solid food. Second, if you have the right stuff in the fluid, it's absorbed better than plain water.
The best mixture involves some carbohydrate with electrolytes (minerals like sodium and potassium). The purpose of the electrolytes is twofold: first, they replace some of the minerals you lose in your sweat, and second, they help get the carbohydrates and water through the lining of the gut and into the blood stream. An energy drink containing carbohydrate and electrolytes that is mixed to about the same concentration (osmolarity if you want to get technical) as the blood is called and isotonic drink. If your preferred energy drink doesn't have electrolytes in it, you can add some yourself by tossing in a pinch of salt (or Lo-salt, a mix of potassium chloride and sodium chloride) per liter of drink.
The most useful form of energy drink is the powdered kind that you add to your water. This is cheaper than the liquid kind, and it is easy to carry with you to put into your water when you refill your water bottles.
You'll get the best effect (in terms of feeding your muscles energy) if your drink is 5.5% to 7% carbohydrate. Since most energy drink powders are close to being 100% carbohydrate, 1 gram of powder will give you 1 gram of carbohydrate. Thus if you add 55 to 70 grams of your favorite energy drink powder to a liter of water (or 44 to 56 grams per typical large water bottle) you'll end up with the right mix. The best thing to do is use your kitchen scales to find out how many teaspoons give you the right number of grams, then just use the teaspoon to measure out the stuff.
If you have a higher concentration of carbohydrates than 5.5% to 7%, this will inhibit the absorption of the fluid, so this is not the thing to drink when you're exercising. However it's fine after you're finished to replentish the stores of energy in your muscles. A lower concentration of carbs is fine, especially if you don't like the sweet taste you get with the proper isotonic mix. It doesn't give you as many calories per gulp, but if it tastes better you'll end up drinking more, which is usually beneficial.
Be careful with mixing instructions on the package: often they suggest you to use quite a lot of powder, resulting in a solution with more carbohydates than the recommended amount for an isotonic beverage.
As for which energy drink to buy, I'd suggest getting the one that tastes best to you. If you want to be more scientific than that, here are some things you can look for. There are different kinds of carbohydrates. Maltose, dextrose, fructose etc are simple sugars which are broken down and get into your blood very quickly. There are "long chain" carbohydrates such as maltodextrin which take a bit longer to break down, and thus provide a more steady release of sugars into your blood. Maltodextrin isn't really sweet, so some products with lots of it use artificial sweeteners to make the drink taste sweet. If you object to this, you'll want to avoid those drinks.
If you want an isotonic drink, but don't want to pay the price for these special powders, take fruit juice and dilute it with an equal amount of water. Add a pinch of salt or Lo-Salt per liter for electrolytes.
If you're cycling along at a decent pace for more than say a couple of hours, you'll need something to eat. Many people use energy bars, but I think they are a waste of money. As far as I can tell they aren't any better for you than carefully chosen normal (not exercise specific) foods. Basically, what you want to look for is something with lots of carbohydrates and low in fat (say less than 15 grams of fat per 100 grams of product). Good snacks that fall into this category are:
Avoid things like high-fat cereal or granola bars, or flapjacks, as they are too high in fat. Although they've got lots of calories, it will take longer for your body to break it down and make use of it.
- malt loaf
- fig rolls (aka Fig Newtons)
- low-fat cereal bars (granola bars). My favorite ones in the UK are Jordans Frusli bars. Quaker Harvest bars are pretty good too.
- fruits, dried (raisins are easiest to digest) or fresh
- Kellogg's Nutrigrain bars
- Garibaldi biscuits
It's important to get some carbohydrates into your body soon after you finish your ride. During the first hour after you finish exercising your body is especially efficient at replentishing energy stores in your muscles, so getting some energy to them then will help you prepare for your next ride. As when you're riding, the best form of calories is carbohydrates. The same foods that are good at feeding you during your ride are good for a post-ride top-up, but since you're more likely to be home you can treat yourself to something requiring a bit more preparation like pasta.
Riding your bike causes small amounts of damage to your muscles (that's what that gentle ache in your thighs means). Thus a small amount of protein in with your post-ride snack can help to repair any damage. But there's no need to overdo this: the amount of protein you get in yogurt or baked beans on toast will be plenty sufficient.
If you don't feel like eating solid food, your energy drink can be used for this post-ride replenishment. If you've been drinking enough during your ride your main concern won't be hydrating yourself, so you can mix up the energy drink a bit stronger than you would when you're riding. However, I often find myself quite thirsty after a ride (probbably not drinking enough) so I mix mine up fairly weak so it doesn't interfere with fluid absorption. As above, a small amount of protein can help to rebuild muscle, so I've taken to drinking Boots protein/energy drink after a ride (mixed up about half the concentration they recommend, 2.5 scoops per 500ml). It's easy to mix up and tastes good to me. My boyfriend hates it however, so tastes do vary!
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For longer rides, you'll want to eat a real meal while you're out riding (typically lunch) in addition to snacks. You should choose this food carefully, as well as the breakfast you eat before starting. For breakfast you want to put complex carbohydrates into you. These will be broken down slowly, providing a steady source of energy. You should avoid highly sugary breakfasts, like donuts. These can cause your blood sugar level to skyrocket, and then a rush of insulin in response brings your blood sugar levels way down, leaving you with little energy for cycling.
The best lunches are again high in carbohydrates. Examples are: baked potatoes, sandwiches with thick bread, anything with rice, and pasta. You can eat fatty things, but they will take longer to break down. Also, a moderate amount of sweets won't hurt to boost blood sugar levels a bit.
If you're spending all day out riding, you'll need to eat alot. When I'm touring I'm riding all day for days at a time, and I tend to settle into this pattern of eating: eat a big breakfast, have a decent-sized snack around 11am, have a good-sized lunch around 1 or 2, have more snacks at 3 or 4, have a decent early dinner after cycling, at around 6 or 7. I found that I needed to eat lots of food early in the day, when I was cycling, and I didn't need any food after dinner. I estimate that I consume somewhere between 1.5 and 2 times my usual caloric intake while touring.
For balanced-diet considerations, I found it hard to eat enough fruits and veggies whilte touring: typical breakfast foods seem to be high-fat eggs & bacon, and dinners often come with high-fat chips (french fries) instead of rice or salad. I often found myself selecting dinners based on the quantity of veggies they came with. You can also increase your fruit intake by stopping in villages to buy bananas and other fresh fruits for immediate consumption. Several times I remember seeing a bunch of bananas hanging in a store window and being irresistably drawn in to buy them.