Why not? Cycling doesn't burn that much energy (for me that's like 300-400 kcal at 60-70 % MHR for those 20 mi/32 km) and depending on what you do at the gym you may not burn a lot either, so especially for someone who's used to eating a lot it may not be hard to still overeat. edit:   My problems are because of the drink and the takeaways when I did drink. One night, every night, was about 3-5000 calories.  Confirmed.