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.
| Study | Glycogen | Lean Body Mass/ Fat-Free Mass |
| Phinney et al., 1980
Untrained, obese subjects |
Week 1:
0.87 mg/100 g wet wt (−43% from baseline) Week 6: 1.04 mg/100 g wet wt (−21% from baseline) |
|
| Phinney et al., 1983
Trained cyclists |
Week 4:
0.76 mg/100 g wet wt (−54% from baseline) |
|
| Bogardus et al., 1981
Untrained, obese women |
Week 1:
0.81 mg/100 g wet wt (−54% from baseline) Week 6: 0.86 mg/100 g wet wt (−51% from baseline) |
|
| Lambert et al., 1994
Trained cyclists |
Week 2:
Approx. 0.7 mmol/kg |
|
| Krotkiewski et al., 2000
Women |
Week 2:
−40% from baseline |
Week 2:
-2.4 kg |
| Harber et al., 2005
Metabolic ward |
Week 1:
−20% from baseline |
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.
| Study | Total Body Water | Lean Body Mass/ Fat-Free Mass |
| Vargas et al., 2018 Resistance trained men (8 weeks) |
−0.3 kg | |
| Yang and Itallie, 1976
Obese men, metabolic ward (10 days) |
Approx. −4.8 kg
(estimated from graph) |
|
| Johnstone et al., 2008 | Week 4:
−0.95 kg |
Week 4:
−1.2 kg |
| Sawyer et al., 2013 | Week 1:
−0.84 kg (men) |
Week 1:
−1.13 kg (men) |
| Gomez-Arbelaez et al., 2017
Obese patients |
Maximum ketosis
−2.3 kg Ketosis declining −2.1 kg Out of ketosis −1.8 kg |
Maximum ketosis
−4.2 kg Ketosis declining −4.4 kg Out of ketosis −3.7 kg |
| Colica et al., 2017
VLCKD1 group |
Week 3:
−1.55 kg |
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
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].
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
Habituation to the diet
We have reason to believe that the body adapts to the ketogenic diet. With time, glycogen stores may return to normal.
“... initial depletion of muscle glycogen induced by the [ketogenic diet] may be at least partially reversed through habituation to the diet.” - Schick, 2016
For example, keto-adapted endurance athletes had normal muscle glycogen levels in Volek et al., 2016. During exercise, their glycogen utilization was similar to the control group, but their glucose oxidation was much lower.
"... the LC athletes had similar rates of glycogen repletion compared to the HC athletes, despite receiving a negligible amount of carbohydrate after exercise (4 vs 43 g) ..." - Volek et al., 2016
We also see that glycogen stores refill over a couple of weeks on the ketogenic diet, such as in Phinney et al., 1980. However, this is not supported by all studies.
One of the mechanisms here is that carbohydrate oxidation decreases so that glucose can be more readily taken up and be converted to glycogen (Harber et al., 2005). The body seemingly adapts by preserving glycogen stores (Schick, 2016).
Strength Training to Retain Glycogen and LBM
Many studies report that the ketogenic diet leads to loss of lean body mass. The good news is that this is to a large extent water and glycogen.
One way to partially prevent glycogen loss, is to do strength training. This is because it leads to glycogen and water gains in both the short and long-term.
“[strength training] induces ... a rise in cellular hydration.” - Riberio et al., 2017
Per the graph below, we see studies where subjects were able to maintain or increase lean body mass with strength training on a ketogenic diet. However, several of the studies have major methodological and data reporting issues. Some studies also find that lean mass is reduced, even with strength training.
Carb refill and supercompensation
We can increase low glycogen stores by eating more carbohydrates. This will lead to a supercompensation effect. Check out the figures by Toomey and Wilson below to see this effect in action.
Figure by Toomey et al., 2017.
Figure by Wilson et al., 2017.
The keto group (red) increased carb intake between weeks 10 and 11, and supercompensated glycogen stores. Hence, a very large increase (+3 kg) in lean body mass.
Salt and Creatine
Finally, you should consider increasing mineral intake and supplementing creatine. Creatine leads to greater intramuscular water retention. You will also need to drink more water if you’re going to do this.