i know exactly what you mean. I can eat like 4 LBS of cucumbers in one sitting and still feel like I could eat a pizza afterwards. when you consume super low calorie foods like cucs and tomatoes, zuchinni, the body actually keeps on counting the calories with incredible accuracy and adjusts your hunger/appetite accordingly. But, I'll say, it does help a little bit and you do get a bit of discount by going with low calorie veggies, it's just not a silver bullet. at the end of the day you'll still consume less calories than you would have: just don't expect one large salad to fill you up. at the end of the day, you still need to go hungry to loose weight or keep it off.

You actually need fats to poke the satiety receptors.

fats don't all do that well on satiety studies. just look at the holz studies. most of the satieting things didn't have much fats in them: potatoes, apples and oranges.

I don't think that only caloric content matters. How satiating do you find a 150-calorie small bag of Doritos compared to three or four grapefruits, with a similar caloric content? For me the answer is "not very."

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 about half an hour. Because 2 large tomatoes does absolutely nothing. Only problem is that 5 large tomatoes will leave me feeling kind of gross with that much volume.

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.

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.

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).