My weight loss stopped.
I came across this little study that put things into numerical perspective for me:
Glycogen Storage: Illusions Of Easy Weight Loss, Excessive Weight Regain, And Distortions In Estimates Of Body Composition
Glycogen is animal starch, a storage form of carbohydrate in our bodies. It's very branched, very susceptible to enzymatic breakdown, and so, very available when we need quick energy. We carry about 1 or 2 pounds of glycogen in our bodies, depending on our genes, our gender, our fat-free mass (more muscle = more glycogen), our recent energy expenditure, and what we've eaten in the last few days. It's very variable.
The study above put 11 women on a ketogenic diet for 10 weeks.2 A ketogenic diet is one that expends stored glycogen, requiring the body to mobilize fat for energy. When too much fat is mobilized at once, such that it cannot enter the Krebs cycle, the body holds these excess fat-mobilization products in the form of ketone bodies. Thus, ketogenic, or ketone-forming diet.
After 4 days on the diet, glycogen depletion was measured.3 There was an average loss of 400 g (0.88 pounds) of glycogen. One of the women was measured as losing 1 kg (2.2 pounds) of glycogen in those 4 days.
The water-binding capacity of glycogen is estimated to be between 3 to 5 times its own mass. Thus, a loss of 400 g of glycogen could be associated with up to 2000 g of water. So, 400 g glycogen plus an associated 1600 g water (1:4 ratio) would result in a loss of about 4.4 pounds in 4 days.
Below are the study participants' total weight losses after 4 days of dieting.
Blue bar = Total weight loss
Red bar = Portion of weight loss estimated to be glycogen loss
Yellow bar = Portion of weight loss estimated to be glycogen+water loss
Click for larger.
I can see that these methods of assessment aren't an exact science, and that individual variability is difficult to account for.
The women went on to lose more glycogen, and more water (and, of course, more fat and protein), during the remainder of the 10-week study. Most glycogen loss occurred at the beginning.
When carbohydrates are added back to the diet, the body preferentially replenishes glycogen stores, along with associated water. The authors of this study stated:
"It is necessary to account for these losses before comparing effectiveness of weight-loss methods."So, maybe 8 to 10 pounds of weight lost on a ketogenic diet could very well be the result of water and glycogen loss, both of which will be restored when the diet is halted ... perhaps at even higher levels than when the diet was initiated:
"Bergstrom et al demonstrated that muscle glycogen can be depleted to about one-third normal with low-carbohydrate diet for 3 d. After a high-carbohydrate diet the glycogen stored rose sixfold higher, to more than twice normal. This excessive glycogen repletion, with associated water, could follow inappropriate refeeding after dieting, leading to rapid and excessive nonfat weight regain."
2 A very-low-calorie-diet (VLCD). Cambridge claims it is protein-sparing (405 calories: possibly 54 g carbohydrates, 40 g protein, 4 g fat).
3 This particular study measured glycogen depletion via total body potassium depletion, since there is a general assumption that 0.45 mmol of potassium are bound up with 1 g glycogen.
Photo of gallon jug, from here :)
A gallon of water weighs 8.34 pounds, about the amount of fluid this study suggests you could lose by depleting glycogen on a ketogenic diet. And about the amount you may replace when glycogen is restored.
Chart generated by me on a quiet Sunday afternoon when I could have been doing a hundred other things but I put them on hold because, well, I like charts.