How much of a food do you need to eat to get the maximum nutritional benefit of that one food?

Like the potassium in a banana, for example. Is one bite enough to get all the potassium your body needs? Is one banana enough? Do you have to eat a whole bunch of bananas to get the nutritional benefit? And how often? Every day? Once a week? Once a month?

What about the protein in a steak? Will one filet give you what you need, or do you need to eat 5 of them? How often?

I wonder about this when I read the nutritional benefit of, say, garlic. Who even eats enough garlic to get any benefit from it?