Carbs in every form (think bananas, rice, potatoes, sugar) are always broken down into the simplest form of sugar in the bloodstream: glucose.
Glucose is then shuttled around to the cells in your body and used as fuel.
When the glucose is stored in the muscle and liver, it is stored in the form of glycogen.
Now here’s the thing: Water sticks to glycogen like a magnet!
What do we mean? For every 1 molecule of glycogen that is stored, there are also 3 molecules of water stored as well! That’s a 1:3 ratio.
Simply put, carbohydrates can cause your body to retain some water as they are stored. And guess what? Water can weigh a lot!
Couple that with the fact that it can be really easy to consume a pound of carbohydrates in a day.
Roughly speaking, that pound of carbohydrates you consume in a given day can hypothetically pull in 3 pounds of water into the body.
This is what is causing the weight fluctuation inside the body. It’s not instantaneous fat gain, it’s water being retained.