In attempting to preserve lean body mass, what is the relationship of body composition to caloric need: Is it true that no matter how lean a person is, the same amount of calories is needed to preserve lean body mass or the leaner a person is, the more calories are needed to preserve lean body mass? Which one is true? And thank you.

Why is margarine better than butter when margarine is just oil that is hydrogenated, which means that extra hydrogen atoms are added to oil (liquid) to make it firm? If oil is hydrogenated into butter, there would be no difference between butter and margarine because they would both be saturated fats with single bonds and the same number of hydrogen atoms. Is margarine really better than butter?

1) When I do a 3-mile or 5-mile run, I run for time and try to finish with nothing in the tank. The closer I get to the end, the more I push myself, because I know I don't need to sustain the effort much longer. When I stop running, I suddenly get very light-headed and dizzy. It never happens while I'm running. I walk briskly while I'm warming down, but that doesn't prevent it. Why does this happen? Is it dangerous?

2)  Sometimes after jogging a while, or cycling a great distance, my head begins to spin and I feel as if I'm going to pass out. Is it normal to have feelings like these, and if so, how intense should these feelings be?

How can you tell when you're full? I am not over-weight, but I tend to over-eat. How can I know when to stop?

1) Is it better to eat before or after exercising? I've recently started a fitness program and am not sure which way is the best.

2) Is it bad to eat before you have practice or a game in basketball?

Does banana have fat like avocados or olives? If so, what kind of fat does a banana have? Thanks.

I find that when I eat lunch I can feel myself instantly get tired as if a wave passes through me. My face gets a feeling of being sweaty and flushed. Coffee and copious amounts of water help counteract this. Also, it doesn't happen every day with every meal. Very small amounts of food don't cause this. It's as if I eat above a small threshold, then it happens. It makes it hard to work. A short nap would be perfect (but not possible). Is this something to be worried about?