Losing Water Weight: How Carbs Really Work

Does going on a ketogenic diet mean you have to stay on it forever? Will keto work for me? Why do many folks experience a few days of low-energy and moodiness (“low-carb flu”) at the beginning of ketogenic diets? To answer these questions, we must first understand our body’s relationship with glycogen.

What’s glycogen?

Many people ask if is glycogen a carbohydrate. Glycogen is the way the body processes and stores glucose as energy, chiefly in the liver and the muscles. High-intensity activities like sprinting draw upon the glycogen tucked away in our muscles for fuel, which is why you hear about marathoners “carb-loading” in the days before a big race.

The glycogen stored in the liver is what keeps specific systems running all day, including the brain, kidney cells and red blood cells. For anyone not on a low-carb meal plan, the body needs a minimum of 100g of glucose each day in order to meet the basic demands of the brain.

So, what happens if a person consumes significantly less than 100g of carbohydrates in a day? What happens when the body runs out of glycogen stores? Well, it’ll have to call on other forms of energy.

The hierarchy of energy sources

Your body gets it’s energy from the easiest sources possible as long as they’re available. The zippiest energy comes from carbohydrates in the diet, especially simple carbs quickly converted into sugars (white bread, sweets, fructose, etc.) with more complex carbs following shortly after.

For a person following SAD (Standard American Diet) — which amounts to nearly 300g carbohydrates a day on average — the body may never burn through this ingested potential energy. Instead, it simply sweeps it away under the rug — you know, the one bulging around your waist — where no one will ever notice. However, when you cut ingested carbs down to less than 100g per day something quite interesting happens: the body burns through those consumed carbs first, then turns to the glycogen stores in the liver to maintain its basic system functions. When those stores run out, usually after about one day of carb deprivation, even more magic happens.

Gluconeogenesis: The body’s back-up plan

If there’s no more glucose or glycogen to be had, a process called gluconeogenesis begins in the liver (“gluco” = glucose, “neo” = new, “genesis” = to make).

Gluconeogenesis is the reason why you don’t actually need any dietary carbohydrates whatsoever to keep rattling down the street. When faced with low carbohydrate intake in the diet, the liver will kick into gluconeogenesis gear, generating the glucose necessary for brain function from glycerol in lipids and amino acids in proteins.

However, getting your glucose through gluconeogenesis is a long process. Consider those marathon athletes again. There is a phenomenon known as “hitting the wall,” which is when the body reaches total exhaustion because no more energy is to be had. This is a direct result of glycogen depletion in the muscles. For non-marathoners, glycogen depletion is generally brought on by switching to a low-carb diet and the first few days of eating this way bring on similar feelings of “hitting a wall.” This feeling is also known as the Atkins flu, induction flu, keto flu or low-carb flu, and is marked by 2-3 days of nausea, headache, low-energy and irritability.

What lies on the other side of the flu is excellent news for anyone looking to ditch the jiggle because the best alternative energy source for the newly adjusted body is its fat stores. After overcoming the “flu” and breaking past the wall, you’ve now entered fat-burning mode!

Is it really fat? Losing water weight

It’s common for those new to a low-carb lifestyle to lose a significant amount of weight at the very beginning of their carb restriction. That could mean four, 10 or even 12 pounds in the first week or two depending on a person’s starting weight. You might ask is this rate dangerous?  Not always.

It’s all about the glycogen stores.  Each gram of glycogen is associated with 3-4 grams of water. So, as your body burns its way through the reduced dietary carbs and into the glycogen stores, the water attached to the glycogen flushes away as well, resulting in the phenomenon commonly known as “losing water weight.” There’s no fat loss here yet — it’s like the glycogen and accompanying water are squeezed out of your muscles and liver.

This also explains why plenty of folks experience an alarming weight gain in the day just following a cheat meal. Even if the ingested carbs are at a moderate level (i.e. consumption of a grilled cheese sandwich, not an entire deep-fried birthday cake), your liver and muscles snatch up as much glucose as they can take, including up to four grams of water accompany each gram of glycogen.

Will all the fat burned during ketosis return?

One of the most persistent warnings low-carb naysayers have regarding losing weight in a ketogenic state is that “you’ll just gain it all back once you go off the diet.” This isn’t the whole truth. The water weight resulting from glycogen stores will return almost immediately as soon as you switch back to ingesting more than 100g/carbs a day — that’s just the nature of glycogen storage. Any weight gain beyond that is as a result of caloric surplus, not anything having to do with coming off ketosis.

The bottom line

  • Glycogen is a way the body stores glucose as energy
  • Under 100g/carbs/day will begin to deplete glycogen stores
  • Switching away from glycogen as your principal energy source causes the “low-carb flu”
  • Glycogen binds with water molecules; flushing it away results in loss of “water weight”