Hey Diz
It's more the
carbs from the previous day that make all the difference. If you've got plenty of glycogen ready for use from the previous day, your body will fuel you through exercise even if you haven't eaten yet (which is why we can exercise first thing in the morning on an empty stomach without passing out). However, try to make sure you have carbs again before the next time you work out - if you are exercising every afternoon, then on your 'up' days try to have something like cereal or fruit for breakfast to give you plenty of carbs ready to use as fuel later on.
On the 'down' days, you'll use up a lot of your body's glycogen. If you then don't eat any carbs until the following morning, you may not have enough in your system to work at your best in the afternoon of your 'up' day. If I'm teaching a class at night and then another one in the morning (or one at 2pm and one at 6pm etc.
), I will eat some high GI carbs immediately after exercise to make sure I have enough fuel in time for the morning. Often this just means something like Lucozade but it does give me a good excuse for chocolate on a regular basis
. If I'm not teaching until the following evening, however, I will stick to low GI carbs.