There are a lot of factors when it comes to weight.
You can lose a significant amount of fat one week without knowing it until the next due to water retention.
There are 2 main reasons you hold water and both have no real relation to how much water you drink -
1. The most important to understand so you know why your weights sometimes stay high right up until the last day of the dieting week on the Smart Diet (Although Thursday is the last day, it is generally Friday mornings weight that informs you of the weeks result which is your true weight).
The reason is that every time you consume carbohydrates you also store 4x the amount of the carbohydrate in water to create glycogen (energy storage within muscles and organs).
So 100g of carbohydrates can cause up to a 500g weight increase (water not fat).
You must however consume carbohydrates to boost metabolism and ensure that your body does not adjust to store carbohydrates as fat (generally associated with low carb dieters).
Every time you eat protein or carbohydrates you refill part of the lost muscle glycogen so your weights will stay high until your body gets a chance to utilise the stored energy without being constantly refilled.
So we intentionally limit the consumption of the main nutrients on your last dieting day to see the results on the following morning after water has been released with the glycogen energy that is used.
This also allows for more room for the additional weekend carbohydrates.
2. Consuming access salt will also make you hold water however this water is held around your entire body and not within muscles and organs as is with glycogen.
This is the water retention you can actually see which makes you look larger.