It’s not uncommon to feel hungry and tired the first week. The reason: You may not be used to eating every 3 – 4 hours, and instead have either gone long periods of time without eating, grazed throughout the day, or a combination of both. Your body needs time to adapt, but it will definitely adapt, usually within a few days or weeks at most. Stay patient and stay the course.
What you are experiencing is quite common for anyone coming off of a low carbohydrate diet when introducing carbs into their system.
When you transition to RP from a low carb diet (which can include the Ketogenic diet), your body quickly burns through its stored intra-muscular carbohydrate, called glycogen. For every gram of stored glycogen, at least 3g of water is stored as well, so when your body depletes stored glycogen on a low carb diet, lots of water loss occurs. When you re-introduce carbs on a diet such as the RP Diet, glycogen gets reloaded into your muscles (which is excellent for building muscle and improving sport performance) and water comes along, temporarily increasing your body weight for a week or two. This weight is NOT fat tissue and is actually a sign that you're eating to support performance and muscle retention, so it's nothing to worry about.
Please check out these articles from people who transitioned from low carb diets to RP