40 Miles?!?
I'm impressed.
I'm assuming that you will either be biking at a high intensity or intervals.
This means that your body will be relying on glucose for energy.
I suggest you take in some slow burning/low glycemic carbs before you go biking.
There is no chance that your body will store fat if you take in some carbs before a 40 mile bike ride.
Try something like oatmeal, yams/sweet potatoes or whole wheat bread along with a good protein source before you go riding.
Your body will eat away at muscle if you do not have a little carb up before
a 40 mile bike ride.
Stay away from all fruits(fructose) before and after your bike ride.
The fructose will be virtually useless for energy or recovery.
Fructose restores glycogen in the liver before the muscles.
Our entire bodies are glycogen depleted when using a low carb diet.
We ALWAYS want to restore glycogen in the muscles before the liver.
Stick with the complex carbs I mentioned above and avoid the fruit
I gurantee you will have the energy to make it through the bike ride
and you will limit the amount of muscle you burn.
Have a good time on your next bike ride