Ok, I'm not sure what's going on here. That does sound like a lot of plant matter, but potatoes don't have much fiber or other low-caloric content; they're 3.7

Ok, I'm not sure what's going on here. That does sound like a lot of plant matter, but potatoes don't have much fiber or other low-caloric content; they're 3.7 kcal/g dry mass (going by the same Russet data point), compared with 4 kcal/g for pure starch. Is it really such a struggle to get enough calories (and protein) from something with 92% of the energy of pure carbohydrates? Do power athletes normally eat a very high fat diet to get enough calories? In my own experience: I eat 3 meals, generally within an 8 hr window, and it's not unusual for me to cook myself a 1 lb bag of lentils as the major ingredient of any one of them. I don't weigh my prepared food, but comparing usda data for "lentils, raw" vs "lentils, boiled" I'm getting a factor of 3 mass difference for isocaloric quantities; I usually have 1.5-2 x 4 cup bowls of food per meal, which is consistent with the calorie-based estimate of their weight increase on cooking. (Sorry to mix imperial units into it, but I'm surrounded by them!) Translating to respectable units, that comes to over 4kg/day of plant matter. I'm apparently smaller than a female powerlifter and certainly get less exercise; the reason this is an equilibrium amount of food for me is I only eat every other day[1]. I don't have any trouble eating that much, though the quantity of food was daunting when I starting alternate day fasting a few years ago. So, I'm inclined to think that the answer is: what sounds like a huge amount of plants is actually a manageable amount of food once you get used to it; it is a lot of volume, but digestive tracts are adaptable and plants are mostly water. [1]: if I have convinced you yet that I am crazy, please try not to let that cloud your judgment of my reasoning :)