It means jack stuff if you aren't eating properly really. For example, an hour of hardcore bicycling is wasted if you pig out at a fast food place.
I don't eat fast food because it makes me sick.
My diet is:
2 sandwiches for lunch. Ham, mayonaise and butter. I use white or brown bread, whatever's there.
Dinner. That's usually 3 potatoes, some kind of green vegetable, and meat, usually steak or chicken.
Late meal for myself. Usually noodles or some home made pancakes c:
2 litres of water.
A smoothie or two if I'm not lazy. All kinds of fruit are used here.
And that's all I eat daily. I don't eat sweets because I hate sweet tasting things.. apart from maple syrup. I don't eat fast food because it makes me sick.
Yet I still have a beer belly. I'm quite strong though, and kind of tall.