The science behind rapid weight loss during the 1st week or so of Low Carb (i.e. Induction) and why it eventually slows down

This post is dedicated to explaining the title phenomenon and what you can expect to experience on a low Carb diet. I’m not a medical professional but I know some science and I’ve studied low carbing for some time.

I’ve see too many post from, mostly newbies, distressed over their rate of weight loss on a low Carb diet.
Here is the typical scenario:
Week 1, they see the scale move down a fraction of a pound or more every day. They are happy, they don’t feel hungry, and they think “Hey, this is easy”.

Somewhere during week 2 or 3 they have a day where the scale doesn’t present a new lower number. Horrors upon horrors, there might even be a day where the reading is higher than the day before. They scream, “I’ve kept my Carbs low. I’m not eating any more calories than the 1st week. I’ve been betrayed! I’ve failed! Low Carb diets don’t work! “ At best they are distressed. At worse they decide that Low Carb is not for them and they quit or move on to something else.

It doesn’t need to be like that. Here is some of the science that explains what is going on and why not only you should you your rate of weight loss to slow, it is actually essential that it does slow down in order for you to lose FAT.

Here is the science behind induction and the rapid loss you see in the 1st week. On a
Normal, high Carb diet your body stores glucose in your muscles and liver in the form of glycogen. Glycogen is a glucose molecule attached to several (3 to 7) molecules of water. Glucose is an easy to use source of energy for your body. All Carbs that you eat eventually get broken down into glucose and they your body uses that glucose for energy. When people speak of “blood sugar” glucose is the sugar that is being measured.

During induction you cut way down on Carbs (all Carbs get broken down into glucose) so your body starts using the glycogen stored in your muscles as a source of glucose for energy. Recall that glycogen is glucose and a bunch of water. As it uses glycogen all of those associated water molecules get released and excreted also. This is why you experience rapid weight loss which is mostly water and glucose during the 1st week of a very low Carb diet.

Many people are trying to “get into ketosis” a state where your body is burning fat for energy and in the process producing ketone bodies in the process. You can smell these on your breath, in your sweat, and they can be tested for in your urine. Under very high energy needs periods (intense exercise) your body will consume ketones for energy. During periods of lower energy demand excess amounts of ketones will be excreted in your urine and can be detected with a test strip. Ketones in your urine are a sign that you are burning a good amount of fat for your energy. That fat can be from your body’s storage or in can be from what you eat or a combination of both. Calories do count. If you eat way above your TDEE (Total Daily Energy Expenditure) you will not be losing weight no matter what diet you are on. Lack of ketones in your urine is not a sign that you are not burning fat. You can be burning fat and consuming all of your ketones with intense exercise. Following a tennis match I’ll show no or only a trace amount of ketones in my urine but the odor or my shirt tells me that there were plenty of them in my sweat. A day or two later there will be high levels in my urine. You can also be burning fat as too slow a rate for ketones to build up in your bloodstream to the point where they will be excreted in your urine. Testing yourself really is not necessary, but if it gives you a send of reassurance then go ahead and test.

You will not enter ketosis until after the rapid weight loss stops. The rapid loss is a sign you are using up glycogen stores. When they are depleted your body will start using stored fat for energy. THIS IS YOUR GOAL right?

Why does my weight loss slow down? I haven’t changed anything!

1 lb of fat has 3500 calories. 1 lb of glycogen/water has 500 calories. Everything else being the same (calorie deficit wise) you'll be losing weight at 1/7th the rate while burning fat as when you were burning glycogen. If you lost 7 lbs in your 1st week on induction it is not a surprise at all that you'll lose 1 lb/week by your 2nd or 3rd week. ONE POUND A WEEK IS GOOD!!!!!!!!!!!!!!!!!!! It is not a failure. It is success.

Let me repeat and emphasize:
1 lb/week good rate of weight loss (500 calories/day deficit)
2 lb/week aggressive rate of weight loss (1000 calories/day deficit)
3 lb/week VERY aggressive rate of weight loss (1500 calories/day deficit) Without exercise you probably have to be on one of those medically supervised liquid diets. With exercise it can be done but you’ll probably not be able to perform at your peak levels.

So, you were happy with losing 5 or 10 lbs in the first week and now your rate of loss has slowed to just one lb/week. You think that somehow you have failed. You have not. The fact that your loss is slowing is success. It means that you kept your Carbs low enough to force your body to consume all of its glycogen stores. Now the good part comes where you are burning the fat stores. Because fat has so many more calories/lb than glycogen your weight loss will be slower, actually more reasonable. You probably didn’t put all of that fat on your body in 5 lb/week increments. It isn’t reasonable to think that it will come off that fast.

Just remember, as fast as the glycogen/water weight came off it will come right back on if you return to a high carbohydrate diet.

Recapping:
When people say that all the weight you lose on Low Carb is water weight they are partially correct. You do lose a lot of water weight that first week or so, you also lose real glucose weight. Then you move into the OWL (Ongoing Weight Loss) phase. Now there isn’t any more water weight left to lose. What you are losing is fat, but because fat is so calorically dense your rate of weight loss will be slower than the crazy high rate that you experience during the first week or so of induction.