So, its been a little over a year since I quit smoking. In March, I started doing push-ups 3-4 times a week, either on the ground or on handle bars. I'd switch around the number of sets, reps, strength settings on the handlebars, etc. I went from not being able to doing 10 regular push ups to doing a little over 45 (I lose count when I max out).

I realized doing too much upper body makes me look weird, so this last month I got a bike & I've been biking to work & back (a little over 6 miles each way, sometimes farther if I take the scenic route). I guess I've been biking around 4-5 days a week, and do it with a relative amount of intensity.

When I started biking, my appetite shot through the roof. I am 5'7 and weigh around the 160's. I used to eat small moderate meals, now I seem to get some serious hunger. The smoking addiction is far gone, so its not that, but I am sure its related to more intensive cardio. Basically, what will happen if I keep working out hard and eating hard?

As long as its true hunger and good healthy food there is no problem. id say not eating when your hungry would be worse for u

It is your body's way of telling you it is running out of fuel. If you do not eat enough to sustain your new level of activity, you will lose weight. It is impossible to give sound diet advice without seeing what you are eating now (everyone's ideas of small, moderate are different) but on the assumption that you are eating a well-balanced diet with proteins and complex carbs, you would want to increase the number of times per day that you are eating.

I don't think you are going to look top-heavy by doing 45 pushups 3-4x / week. I am 47 and do 5 sets of 20 every other day and don't do specific lowerbody weight training but do cycle 3 - 4 x week and don't feel top-heavy at all. I am 6'0" and 205.

You didn't say if you are trying to lose or gain weight or stay the same? With increased exercise you can certainly expect increased food intake and some increased wieght in the form of increased muscle mass.

What happens if you work out a lot AND eat a lot?

That's the story of my life. Eating big is good if you're burning it and/or fueling gains

More info needed I'm afraid, how many calories are you taking in daily?
Also, pressups don't count as a workout, especially if you're doing 45 per set, that's more of an endurance exercise.

Do you lift weights at all?