I know doctors want you to lose some weight to reduce the size of your liver so it's easier for them to operate. But really how much do you need to lose to make that kind of difference? I see some people only lose like 8-10lbs, some people a lot more. Will it really make much of a difference if you only lose a little bit? What about patients with a very high BMI (68)? I'm assuming they'd have to lose a lot more before surgery?

It isn't weight loss that causes the size of your liver to shrink, it's eating a low-carb, low-sugar, low-calorie diet. This forces the liver to extract its stored energy and use. Eating that kind of diet also usually causes weight loss, for sure, but they don't necessarily have to go together. Two people could eat the same diet for two weeks before surgery and lose different amounts of weight due to different starting weights, faster metabolism, diffferent muscle density, one person retained more water, the other person exercised more, etc. But their livers should shrink roughly the same amount just based on their food intake. So, don't worry about how much you or anyone else loses, just worry about how well you comply with your pre-op diet plan

What @@Bufflehead said. Losing weight alone doesn't reduce the size of your liver. It is what you are eating. And weight loss is just often a byproduct of the liver reduction diet. Some surgeons will use it as an indicator of whether a patient actually stuck to the pre-op diet as well.

There are two places your body stores sugar as fuel: your liver, and your muscles. Stored sugar is called glycogen. Glycogen molecules are attached to Water molecules at a ratio of 1:4, so for every ounce of glycogen you've got in your liver, you've got another 4 ounces of water. Much of the weight loss on a preop diet or other low-carb diet initially is the glycogen and the water.

Once you deplete glycogen (by limiting carbs), eating carbs again causes you to restore glycogen and water - so the "weight gain" from going off a low carb regimen is actually lean mass and water, not fat.

Hope this helps!