Why do you lose weight so quickly on low carb diets?
I usually have new clients tell me they do much better on low carb diets. When I ask what they mean by that, they say that they have tried low carb diets before, and they lost a ton of weight super fast.
Well my next question usually is along the lines of “Why isn’t it working now?”.
Usually the answer is no one wants to eat low carb for the rest of their life. You want to do things like have cake at birthday parties, going out to eat and not be afraid to have bread before dinner, having a cookie every once in awhile, enjoy Thanksgiving mashed potatoes, and make pancakes for breakfast.
Simply put — low carb diets aren’t sustainable.
But let’s get back to the main point: why do you lose so fast at the beginning of a low carb diet anyway?
Let’s start with the science…
carbohydrates and water storage
When carbs are stored in your body, they are stored in the form of glycogen. This is just an easy way for your body to store quick energy sources so it can use it when it is ready. Glycogen is stored in your muscles and liver. The average amount of glycogen humans have stored is about 500 grams.
Each gram of carbohydrates carry about 3-4x their weight in water. If we say you have 500 grams of carbs, multiplied by 3-4, that gives you between 1500-2000 grams of water. That gives us a total of 2500 grams (500g carb and 2000g water), or 5.5 pounds.
Low carb diets and weight loss
When you eat a low carb diet, not only are you not consuming carbs, but you are actively using the carb stores you have. So the 5.5 pounds you had originally stored in the form of carbs and water, you will lose when you use your glycogen stores (which will happen relatively quickly). So it is no surprise you see big drops on the scale.
Additionally to the water loss, you’ll see some fat loss as well. Fat loss will come from a calorie deficit, regardless of type of diet. When we consider the types of foods highest in calories/are easiest to overeat, what comes to mind first? Probably cookies, chips, donuts, pizza, pasta, etc., all things that are also carb sources. If you suddenly stop eating this giant source of calories, you’ll no doubt be in a calorie deficit. And even on top of all of that, you’re eating less foods than you normally do! Less food sitting in your body=less weight.
All things considered, it’s really not too surprising why you lose weight so quickly on a low carb diet. However, the goal of any diet should be sustainability. Your goal should not be to lose as much weight as quickly as possible. You should instead be looking at how you want your life to look after your weight loss. Do you want to avoid carbs and be extremely restricted forever? Probably not. When choosing how you’d like to diet, think about this first.
I teach my clients a “flexible dieting” approach, which I find the most sustainable personally. Through this approach, you are able to fit foods that you find enjoyable without feeling guilty about them or like they are off limits. It will also lead to a sustainable weight loss of 0.5-1% of total body weight per week. Although you won’t see a drop of 10 pounds in a week like you would with low carb, you can rest assured that your weight loss is directly coming from fat loss.
