I started adding whey protein to my smoothies early this year, because stuff I read indicated that protein is more important to even endurance athletes than previously thought. I'd always had problems recovering quickly enough from hard workouts to feel fresh for the next one, usually I had to take several days off to feel fresh, and perhaps low protein was one of the reasons.
I'm not vegetarian, but adding whey protein was an economical way to get more protein to work on repairing and building my muscles. They generally say that somewhere around 0.9 grams of protein per pound of body weight a day is a good amount to eat. This almost doubled my daily protein intake to around 130g.
Creatine is something I'd read about before, but I always associated it with body building; not what I'm into. Then I started reading more about how it also helps muscles recover from hard workouts, and also helps store more muscle energy. That's a real benefit for frequent, long, high-intensity workouts. And it's naturally occuring in food, just like protein, so no need to worry about whether my body would be harmed by normal dosages. I started adding about 5g of creatine per day to my diet this summer.
I now feel stronger and fresher than before I started adding more protein and creatine to my diet. I've been upping the weights I use for my upper-body excercises too.
The downside is that I have also gained weight, though at least it's not from fat! I keep a detailed diet and workout log, and there's no reason I should have gained any weight based on the calories I consumed versus the calories I burned during this time. It seems that most, maybe all, of my weight gain is caused by the creatine and the water and energy it stores in muscle cells.
But if I'm to do well in hilly bike races I will need to limit my weight. I read that it takes about a month to lose the weight from creatine supplementation, so I suppose I could stop taking it a month before my first priority hilly race of the season to get my weight back down to normal. I will have to carefully balance the costs and benefits of creatine when deciding when to stop supplementing with it.
By the way, how much does weight slow us cyclists down? The Analytic Cycling web site has an online tool for determining how much weight slows you down on hill climbs. And see what my teammate Steve's posted for some great info on his own real-life experience with weight and hill-climbing performance.