Why Does Rapid Weight Loss Occur on Keto?

Chris Irvin
Written By Chris Irvin
On May, 11 2021
2 minute read

Did you know you could lose up to 10 pounds in one week on Keto?

In fact, if you're reading this have tried keto yourself then you have probably experienced pretty rapid weight loss when first starting keto.

The issue is that this leads many to being skeptical. To help ease the skepticism, it’s important to understand where this weight loss is coming from.

The weight lost during your first few weeks on keto comes from water, glycogen, and fat.

However, the primary contributor to the rapid weight loss is water.

To go a little more in depth, when you stop eating carbohydrates, blood glucose lowers causing a subsequent drop in insulin levels.

This makes the pancreas secrete glucagon, which signals for stored fatty acids to be released from adipose tissue and into the blood where they can circulate and be taken in by various cells and used for energy.

However, some fatty acids make it to the liver and are used for ketogenesis, which results in ketone molecules being produced from fat and travel out into the bloodstream, where they can travel to cells.

Ketones have to help activate the transporters responsible for opening the doors for ketones to get in. This process can take some time and is one of the reasons why you see an increase in blood ketones, but a lag time before the benefits of ketosis are felt.

What you do need to know about your insulin levels lowering is that your kidneys are responding by dumping a lot of water leading to rapid weight loss.

Is Rapid Weight Loss Dangerous?

No. While many people may use this as support for keto being dangerous, it’s not. But it is one of the reasons why you experience most keto flu symptoms and why it is so important you stay hydrated while following this lifestyle.

Drinking plenty of water and replenishing electrolytes is so important on a ketogenic diet.

When Do I Start Burning Fat on Keto?

Pretty much right away. Once you start to lower your insulin levels you will turn on fat burning.

How long it takes for this to occur is different for everyone depending on your level of insulin sensitivity when starting keto.

During your first week of keto you are still burning fat but not the main contributing factor to all of the weight you are losing.

As you continue following this keto lifestyle, you will keep improving your fat burning abilities and will start to notice more steady realistic weight loss like 0.5-2 pounds per week.

What About Glycogen Loss at the Start of Keto?

Glycogen is our bodies stored form of carbohydrate. When you first stop eating carbs, your body will likely respond by burning through most of is stored glycogen. It is not a massive supply but it is enough that it can contribute to weight loss, especially since water is also stored with glycogen.


You will lose a lot of weight when you first start keto because of water loss. This is not a bad thing or anything you need to worry about. It is a natural process that occurs as we become adapted to a ketogenic diet. Drink plenty of water and supplement with electrolytes.

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