How much water does liver glycogen carry? The 1941 rat study behind the 2.7 g ratio
Three Columbia University physiologists, publishing in 1941, weighed the water, glycogen and other solids in rat livers to work out how much water is stored with glycogen. A 2021 review of bodybuilders’ peak-week practices cites the paper as the source of the often-quoted 2.7 g figure (Escalante et al., 2021).
What the study did and found
McBride, Guest and Scott, physiologists at Columbia University, published this study in the Journal of Biological Chemistry in 1941. They reworked older rat data and analysed the livers of 100-day-old male rats on different diets to measure how much water is stored with each gram of glycogen.
Reworked, the older data showed the liver’s other solids rising by up to 32% as glycogen built up. Only agar-fed controls and rats given half rations after a 36-hour fast kept them nearly steady, giving 1 g of glycogen to 2.7 g of water, the authors’ best estimate. In fully fed rats with extra liver fat the “apparent” ratio fell to 1:1.9 (McBride et al., 1941).
Why it is cited
The one referring page recorded here is a 2021 peak-week review for bodybuilders by Escalante and colleagues. The record appears as reference 29, linked by its bare Cabdirect address. It supports the review’s statement that the “commonly referenced value of 2.7 g of water per gram of glycogen”, sometimes rounded to 3 g, comes from rat-liver studies.
That use matches the paper, but the review omits the conditions: the figure held only when other liver solids stayed constant, and the authors called their ratios apparent.
The ratio comes from groups of 5 to 19 male laboratory rats and from liver, not human muscle, where most of the body’s glycogen is stored (McBride et al., 1941).
Later human studies are small and indirect. Olsson and Saltin proposed 3–4 g of water per gram of muscle glycogen in 1970, a range a 2023 review still accepts while noting that glycogen-bound water was never measured directly (Shiose et al., 2023).
The topic today
The 2.7 figure still appears in sports nutrition guidance, including a 2025 combat-sports position stand (Ricci et al., 2025), and glycogen water is often used to explain quick early weight loss on low-carbohydrate diets.
For the current picture, see our explainer Does Glycogen Hold 3 g of Water? What the 1941 Rat Study Found.