It’s common for those new to a low-carb lifestyle to lose a significant amount of weight at the very beginning of their carb restriction. That could mean four, 10 or even 12 pounds in the first two weeks depending on a person’s starting weight. You might ask, is this rate dangerous? Not always.
It’s all about the glycogen stores and the association between carbs and water retention. Each gram of glycogen is associated with 3-4 grams of water. So, as your body burns its way through the reduced dietary carbs and into the glycogen stores, the water attached to the glycogen is lost as well resulting in the phenomenon commonly known as “losing water weight.” There’s no fat loss here yet — it’s like the glycogen and accompanying water are squeezed out of your muscles and liver.
This also explains why plenty of folks experience an alarming weight gain the day following a “cheat meal” (like tiramisu). Even if the ingested carbs are at a moderate level (i.e. consumption of a grilled cheese sandwich, not an entire deep-fried birthday cake), your liver and muscles snatch up as much glucose as they can take, including up to four grams of water to accompany each gram of glycogen.