1. If you want to eat less today, you don't have to eat too much: This sentence expresses your desire to eat less because you are not too hungry or want to keep moderate.
2. I'm trying to control my diet and want to eat less: this sentence shows that I'm trying to control my diet recently and want to eat less.
3. I hope to enjoy food while staying moderate, and I want to eat less: this sentence means that I hope to stay moderate while enjoying food, and I hope to eat less.