How big athletes in my college get satisfied by eating a sandwich only?

Then have two sandwiches.
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Perhaps that sandwich is just a "snack" and not their full meal. Getting "full" is not generally a good idea, especially for athletes. It weighs them down and causes them to feel sluggish.
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Not necessarily. It depends on how many calories they are burning during physical activity.
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Maybe they’re drinking like, protein shakes and whatnot. o.o

If that’s all they’re eating, that’s bad.

I swim, 2 hours every day except Sunday, and I eat like a pig to fill myself up. I would die on a sandwich per day.
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Maybe they are not satisfied, but are limiting intake to maintain weight.

Of course, it also depends on the size of the sandwich. Is it a "Dagwood Sandwich"?
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Surprisingly enough, exercise suppresses appetite. You wouldn’t think so, but I know from personal experience (eating disorder). It is not really healthy for them to be doing that though. It will not give them the proper nutriets they need. I am guessing though, that that is not all they eat all day. If you see them before they are doing their sport eating this, it is probably because you can’t do rigorous activity if you’re too full. But as for it satisfying them, I am not surprised.
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Normally athletes and weight lifters only eat large amounts of food when they are "bulking".
But if they are "cutting" this means they eat less food, and they only eat "clean" food.
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