Though the low carb, high fat keto diet was originally devised to help treat epilepsy, many people are turning to it to lose weight.
According to some research, it provides several advantages over other diets, including making it easier to burn your stored body fat, maintain your metabolic rate (the calories you burn at rest), and feel more full on fewer calories (1, 2, 3).
That said, you may wonder how much weight you can expect to lose in your first week on keto. Many people report extreme weight loss when first starting the diet. However, much of this can be attributed to water losses.
This article reviews how much weight you can expect to lose on your first week of keto.
On keto, you strictly limit your carb intake, typically to 50 grams or fewer per day of total carbs, or 25 grams or fewer of net carbs, which are total carbs minus fiber.
For most people, carbs are the body’s primary source of energy. When you limit carbs, your body burns through the carb stores in your muscles and liver — called glycogen — typically within a few days (4, 5).
After this, your body switches to a metabolic state called ketosis, in which it uses ketones that are broken down from dietary fat or stored body fat, as its primary source of fuel (4, 5).
This shift, during which you burn through your glycogen stores and switch to using ketones, usually takes less than a week. However, for some people, it may take longer (4, 5).
Many people notice dramatic weight loss during this transition period after first starting the keto diet, but most of this is due to changes in water weight (6).
When you restrict carbs on keto, your body rapidly burns through glycogen, the stored carbs in your liver and muscles. After your glycogen stores are depleted, you shift to burning fat. Many people notice dramatic weight loss during this transition.
The glycogen stored in your muscles and liver is bound with water, typically at a ratio of 3 grams of water for each gram of glycogen (6).
When you burn through these stored carbs, this water is excreted in your urine or sweat (6).
As such, after starting keto, you may notice that you have to urinate more often and feel much thirstier than normal. You may also notice large weight losses, which are mostly water-weight losses (6, 7).
Depending on your size and how much water weight you’re carrying, this weight loss can vary. Anecdotally, people report losses within the first week of anywhere from 1 pound (0.5 kg) to 10 or more pounds (5 kg).
The larger you are, the more water weight you’re likely to lose after starting keto. Although, it’s unlikely that much of this initial weight loss is fat loss.
However, once you enter ketosis, it’s much easier to utilize your own stored fat for energy, which is one reason why the keto diet may be advantageous for weight loss (3).
When you burn through glycogen, your body releases the water that was bound to it. Much of your early weight loss is probably due to these water losses. Still, you’ll burn more stored body fat once you’re fully in ketosis.
Many people use the keto diet for weight loss, and there are several reports online of dramatic weight loss shortly after starting the diet.
This is likely mostly water weight because as you burn through your carb stores, your body releases the water that was bound to those carbs.
Once you’re fully in ketosis, your weight loss will probably slow down, but it’s likely to be more fat than water.