I fail at this thread. I am about 20lbs under weight, I had just quit smoking in June or July but my room mate broke the "no smoking in the house" rule enough times to get me started again. Aside from that, I don't eat fast food and try to avoid soda. I also try to limit the alcohol intake to a three drink max or perhaps just one scotch. Hearing is another story. Despite doubling and tripling up on hearing protection at work, being around helicopters will make me go deaf at a very young age.
I admit that I have slacked on PT quite a bit, lately.
BON, if you're getting light headed from physical activity, I suggest you go see a specialist. Other than that, to gain weight you could try to eat a lot of carbs. Breads, potatoes, corns, and don't cut out the fat or sugar content. As long as you're not consuming a pound of sugar a day, you should be good. The same does not apply to those who are over weight. I know I end up eating 5% of my weight in meats and starches daily just to sustain my 115lbs.