The Role of Glycogen

Glycogen is the body’s stored carbohydrate. It is mainly found in muscles (~350–700 g) and the liver (~100 g) (Knuiman et al., 2015). The body uses glycogen during exercise, and the more intense the exercise, the more glycogen is used (Knuiman et al., 2015). 4 grams of water are stored alongside every gram of glycogen.

We can reduce glycogen stores by:

Fasting

Restricting carb intake (i.e. the ketogenic diet)

Exercising

Glycogen stores shrink on the ketogenic diet

Since the ketogenic diet restricts carbohydrates, glycogen and water stores drop. This can be seen in the figure and table below:

Resting muscle glycogen levels are more than halved on a keto diet (white bars) vs normal diet (striped bars).

Figure by Bogardus et al., 1981.

Per the table below, glycogen stores are reduced by 20–54% after 1–6 weeks on the ketogenic diet.

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“In humans, most glycogen is made and stored in cells of the liver (~100 g) and muscles (~350 – 700 g; depending on training status, diet, muscle fibre type composition, sex and bodyweight) and can be reduced by fasting, low intake of dietary carbohydrates and/or by exercise.” - Knuiman et al., 2015 “ ... glycogen availability is essential to power ATP resynthesis during high intensity exercise which relies heavily on glycogenolysis.” - Knuiman et al., 2015 “The apparent paradox that ad-libitum intake of high-fat foods produces weight loss might be due to severe restriction of carbohydrate depleting glycogen stores, leading to excretion of bound water” - Astrup et al., 2004

Does glycogen come back?

Please read the relevant sections on habituation to the diet and carb refills [Internal links]

Water and Salt Loss

The ketogenic diet leads to ketosis-induced diuresis (Miller et al., 2004; Pogozelski et al., 2005).

“[Diuresis] — an increased excretion of urine” - Merriam-Webster

In other words, the ketogenic diet has a dehydrating effect. The dehydration happens in part because more salt is released from the body, alongside glycogen and water (as described in the previous section) (Denke, 2001; Miller et al., 2004; Pogozelski et al., 2005). We can see this effect in the figure below, where ketosis leads to a large reduction in the total body water of the participants.

Figure: Gomez-Arbelaez et al., 2017 (edited for clarity).

Participants were obese patients.

Per the table below, total body water is reduced by ~1–5 kg after 1–8 weeks on the ketogenic diet.

Table: total body water is reduced in ketogenic diet studies.

Glycogen may be part of the LBM calculation, so it is important to also look at LBM for reduction in wet weight caused by keto flush.

“Ketone bodies are filtered by the kidney as nonreabsorbable anions. Their presence in renal lumenal fluids increase distal sodium delivery to the lumen, and therefore increase renal sodium and water loss” - Denke, 2001

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“ ... the unanticipated additional weight loss is consistent with the 1–2-kg weight loss seen with glycogen mobilization (in liver and muscle) and ketosis-induced diuresis (increased delivery of sodium to distal lumen of the kidney by non-reabsorbable ketones inducing water loss) that occurs with LC diets. 34,35” - Miller et al., 2004 “Ketosis also causes water loss. The kidney filters ketones as anions, increasing distal sodium delivery to the lumen and causing diuresis [14].” - Pogozelski et al., 2005 “The high-protein, low-carbohydrate dieting resulted in substantial weight loss, probably due to a combination of salt and water loss, as well as caloric restriction” - Larosa et al., 1980

Does Keto Flush Lead to an Illusion of Rapid Fat Loss?

No doubt, you can use the ketogenic diet to reduce hunger and eat less. This in turn will help you burn body fat.

However, it is important that you’re aware of keto flush. The first time you start on a ketogenic diet, you will likely experience rapid weight loss. This might feel like the diet is burning off fat, but the weight loss is also due to glycogen, salt, and water losses.

Several research teams expect people to lose anywhere from 1–5 kg of wet weight in the first week(s) of the ketogenic diet (Kreitzman et al., 1992; Bilsborough and Crowe, 2003; Miller et al., 2004). In other words, weight that is not fat mass.

You can see studies that reported water loss in the table above [internal link].

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“Glycogen losses or gains are reported (2) to be associated with an additional three to four parts water, so that as much as 5 kg weight change might not be associated with any fat loss. As glycogen stores are readily replenished after conclusion of any weight-loss program, it is necessary to account for these losses before comparing effectiveness of weight-loss methods, before assessing recidivism, and certainly before criticizing dieters for lack of post-diet control.” - Kreitzman et al., 1992 “As each gram of glycogen is bound with 3g of water, then a simple calculation shows that a ‘weight loss’ of around 1-2kg can be achieved within the first week of the diet, albeit due to diuresis and not to the burning of fat stores.” - Bilsborough and Crowe, 2003 “Of importance is that a proportion of the BW reduction in the low-carbohydrate/high-protein diet group may have been attributable to body water losses associated with glycogen depletion (13), particularly in the first week of dietary intervention.” - Nickols-Richardson et al., 2005 “ … the unanticipated additional weight loss is consistent with the 1–2-kg weight loss seen with glycogen mobilization (in liver and muscle) and ketosis-induced diuresis (increased delivery of sodium to distal lumen of the kidney by non-reabsorbable ketones inducing water loss) that occurs with LC diets. 34,35” - Miller et al., 2004

Why Keto Flush Makes You Look Deflated

Fat-free mass is mostly water. On average, it is ~73-74%, but the full range in humans is ~69–81% (Wang et al., 1999; Roumelioti et al., 2018). So it should come as no surprise that muscle mass also consists of water and protein. Though, it also contains fat (intramuscular triglycerides), glycogen, and other substances.

When muscle hydration changes, so does muscle size (Nygren et al., 2001; Bone et al., 2016). And as we know, the ketogenic diet reduces intramuscular water and glycogen. Hence, keto flush can make muscles look smaller, but it could also have the positive effect of reducing general bloating.

4.2 kg of Fat-free mass is lost on a ketogenic diet. Figure by Gomez-Arbelaez et al., 2017

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