Your body will let you know. If you do it wrong the message will be unmistakable ;)
Any sudden changes in diet can upset your stomach and it probably doesn’t get more drastic than going from fasting to eating again. I remember when I was training for long distance cycling (north of 100 miles a day). You have to teach your body to eat and digest while riding, something is sure as hell doesn’t want to do. The first protein bar I ate while pushing hard almost ended up puked in the side of the road. After a while I was able to consume 400 calories an hour for many hours straight while clicking the miles away.