[crazygringo]

Grapefruits aren't a good comparison, since Google says a grapefruit has 104 calories.

But if we compare a 150 calorie bag of doritos with 5 large tomatoes (each one being 33 calories), that feels about comparable in terms of satiating me in terms of giving me a break from hunger for maybe 45 minutes.

On the other hand, just large tomatoes does absolutely nothing for hunger. Which is the indication for me that volume is entirely irrelevant. (And why would volume matter? Your body can't turn volume into calories.)

Only problem with 5 large tomatoes is that it leaves me feeling kind of gross/bloated with that much volume. My stomach will literally feel like it protrudes, which is uncomfortable.

[emodendroket]

My mistake. I got misled by the “serving size” of half a grapefruit (who just eats half?). But volume mattering is pretty well attested and most people have experience with it. Why wouldn’t it? You physically can only fit so much food inside your stomach before it is uncomfortable to continue, no matter the caloric content.

[crazygringo]

Yeah I guess that's what mystifies me about it so much. Volume does nothing for me.

Like if I'm on a diet of 1,200 cal/day to lose weight, eating bulky foods does nothing to make me any less miserable, compared to if I stick to dense protein/fats/carbs. The sensation (and distraction) of hunger remains identical.

[emodendroket]

1,200 calories per day is an exceptionally restrictive diet in any case. I think it might be more obvious the difference if you were just eating till you felt full and tried swapping around different foods (though there is plenty of historical record of people resorting to nonfood items of no nutritional value just to fill their stomachs if hungry enough).