Scientific Nutrition Update 32: Low Carb Diets, Glycogen, and the Week 1 Effect

This episode is basically a rant about something that frustrates me that I see all the time in online low carb dieting and ketogenic diet groups.  People do not realize how much of the initial weight loss with low carb diets is water weight.

Script (remember I ad-lib and go off script):

For today’s episode I am going to rant a little bit, and this is coming mostly from my experience spending way too much time on the internet.  So low-carb diets right? They’re pretty popular. But one of the most common things I find when I’m looking in keto groups, or low carb groups or anything like that, is a new member coming in and talking about how they just low 6 pounds in their first week! How they are so excited, they’ve never been able to lose weight like this before and they are excited about what this means for them.  They are going to be very sorely disappointed very quickly. In order to explain why, we need to dive into a little bit of biochemistry first.


So glycogen is one of our body’s methods of storing energy.  It is basically a whole bunch of glucose molecules connected together, and so when your body needs energy it tells your muscles and liver to start breaking down the glycogen into glucose.


So why is this important for us? Well because glycogen is mostly glucose…Meaning that it is primarily a carbohydrate storage tool, and so when you go on a low carb your body will start burning through it’s glycogen stores pretty quickly.  This is not a bad thing but it can be deceptive.


Basically when your body stores this glycogen it also stores a bunch of water with it.  The number I initially learned was for every gram of glycogen your body stores about 3 grams of water, but looking at the literature there is a little bit of debate about this, with numbers ranging from 1:3 as high as 1:17 with good hydration after exercise.  So basically there’s a whole bunch of water stored with this glycogen. However, the way that study was done some of the water could have been stored not bound to glycogen so we are going to stick with approximately a 1:3 ratio.


So what does this mean for our brand new low carb dieter? It means most of that weight they lost? It was water.  They lost some fat, a bunch of glycogen, and mostly water. Now, I’m not saying low-carb diets are bad, but I do think people in these communities can do a better job of explaining what it is that’s happening with this sudden and fast weight loss, and give their members a better expectation that those results will not persist.


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