Originally Posted by
terrymorse
Endurance activity like cycling does consume proteins from the body, which is why cyclists' dietary protein requirements are high. If you get enough protein in your diet, you shouldn't lose muscle mass.
The recommended protein intake for endurance athletes is
1.2-1.4 g protein/kg body weight per day -- almost as much as strength athletes.
Yes, but you also need to get enough total calories as well. Burning more than you take in and as fat stores get low enough the body starts to metabolize muscle and even organs, regardless of the composition of what you eat.