For most people losing a few kilograms would improve performance. So why not try to lose a bit of weight simultaneously as you train to increase fitness?
Training is not super complicated. Nutrition is. I truly believe it is possible to lose body fat, increasing muscle mass and fitness in the same period of time. Doing it on the same day, however, is a different story.
I had my first long ride on the bike after the season break a few weeks ago. It was a 3,5-hour session with 10 min @190 watts (60 % of FTP) followed by 5 min @265 watts (82 % of FTP) in repeat. Coach Carson Christen said I should go for 3 hours, but I aimed for 4 hours as this is not supposed to be a very hard session and I want to get in some longer sessions since Ironman Texas is only a few months away. It felt fairly good, but as I had been riding at 265 watts for 3 hours continuously on the turbo before Patagonman, I did not expect otherwise. After 3 hours, however, I started struggling and on the 5 min at 3 hours and 15 min I barely made it thru. It did not feel like 265 watts, but 365. I counted down every second wanting to quit after 2 minutes and really had to push for every pedal stroke. Basically, I hit the wall.
How was your nutrition? My coach asked me. I had eaten a solid breakfast before the session, but nothing during the first three hours and took my first snack only 10 minutes before I hit the wall. It was intentionally, to increase fat metabolization. I been doing a lot of so-called water only rides and are very good to utilize fat as energy. The last statement was not something my body agreed with. I used to be good to utilize fat, before the season break. Without training those longer fasted sessions for a few months that skill sure decreased.
Only two days after I went on the turbo for another long session. 1 hour @200 watt + 6 x 8 min @255 watts with 2 min @175watt + 6 x 5 min @280watts with 5 min @175watts. It should be a harder session than the previous, but it was far from it. I finished my last 5 min @280watts with a peak HR of 150 bpm. On the session I bonked I had a peak HR on the last 5 min @265watts of 168 bpm(!). The only real difference? I fuelled myself properly. It was nothing magical about it either. After one hour I eat a pear. Then I eat half an energy bar each 30 min after that.
Losing weight often comes naturally when the training volume increases during the periods with long slow distances. It’s better to under-fuel when you are training with a lower intensity, which burns mostly fat, the energy that doesn’t need to be replaced. An intensity and length low enough that it does not challenge your carbohydrate store or total energy utilization.
To sum it up: fuel properly for the hard workouts. You want to have maximum energy available to perform the hard workouts at the highest level possible. Don’t even think about losing weight or restriction calories before, under or after those sessions. Think only about performance before and during, and only recovery afterwards.