[CliffordK]

If you eat foods with glucose the glucose is stored semi-long term as glycogen in the muscles and liver. For every 100g of glucose, the body has to absorb about 300g of water to make glycogen. So if you eat 50g of glucose, you'll gain ~200g of weight, provided you also drink.

Why?

Glucose:  C₆H₁₂O₆
Glycogen: (Glycogenin Protein)((C₆H₁₀O₅)_n

So, every unit, one loses a covalent bonded water molecule.

HOWEVER, other than fat, most molecules in the body would be stored in a aqueous solution.  So, how much water is required to dissolve Glycogen?  I'm seeing a saturated glucose solution in water is about 50/50, so, perhaps the similar for glycogen.

Then there is the weight of the Glycogenin Protein molecule.  It would only count if one is forced to make more of them.

So, direct conversion of anhydrous glucose or sucrose into aqueous glycogen could actually take more weight than expected.

But, of course, there is also ATP consumed (and thus potentially some glucose consumed just to make the glycogen.

[Bored chemist]

I'm seeing a saturated glucose solution in water is about 50/50, so, perhaps the similar for glycogen.

No.
Glycogen is relatively poorly soluble.
Perhaps 20%.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1254356/?page=8
But there's nothing to suggest that it is all in solution while in the liver cells.

[Petrochemicals]

All food is because it gives you the energy to gather more food ?

[wolfekeeper]

For every 100g of glucose, the body has to absorb about 300g of water to make glycogen.

Why?

Not sure about the physics/biochemistry of it, looks like potassium is also required:

https://pubmed.ncbi.nlm.nih.gov/1615908/

[charles1948]

All food is because it gives you the energy to gather more food ?

Your proposition is correct, in the case of predatory organisms.  Who obtain their food, by actively hunting down prey organisms in order to consume them.  Thereby "gathering", to use your term,  extra energy from the prey.

However, a predator has to expend energy in the "hunting "process.  So there must be a point where the energy
lost in hunting, exceeds the energy gained from eating the prey.  Thereby making the hunting not worthwhile, from an energy- balance viewpoint.

I noticed this once, years ago, when a pigeon landed on a roof next to to my flat.
The pigeon was clearly in some distress.  It was hopping about unhappily, trying to holding  one foot up from the ground as far as it could. Evidently it had suffered some injury to its foot and was in pain.

Out of sympathy, I got a slice of bread, broke it up into crumbs, and threw the crumbs across to the neighbouring roof, that the pigeon was on.

I tried to throw the crumbs close to the pigeon, but some of the crumbs went astray and landed quite a distance  away.  Further up the roof.

But even these distant crumbs, were sought after by the pigeon.  It hopped laboriously up the roof to get a single crumb that had landed a long way away.

I thought  " Surely, pigeon, the pain of getting to that crumb, isn't worth the effort"

I don't know what to make of this.  But it has stuck in my mind.