Ripclawe, be weary of having tuna everyday, I've read cases of people getting mercury poison because of eating tuna regularly. Although it may depend on the type of tuna, and how much exactly.
I eat a can of tuna every day, I've done so for about a year (not exaggerating), no mercury poisoning for me. I actually went to the doctor and asked for a blood test, as I too had read about people getting poisoned. He said that it was very unlikely and he was right. The test came back and my mercury levels were completely normal.
There seems to be a lot of conflicting evidence. I think realistically, you would need to eat tuna for every meal/have very large portions over a long, long period to be at any risk.
Anyway, on the topic of weight loss, I was 96 kg (211 lbs) at my heaviest. My lifestyle was terrible, I ate a lot of fast food, drank soda or cordial and did little to no exercise. One day, I decided I had had enough. I started drinking water, eating healthy and exercising. The weight fell off me. I never counted calories, if I was still hungry after a meal, I would eat some fruit. That is also my way of dealing with any temptation, I'll think about having some chocolate for example, then I'll have fruit instead. It hits the spot and I feel good about myself after it.
Nowadays, I weigh 76kg (167 lbs) which is apparently ideal for my height. I still don't eat junk food (3 years since I started my health kick) I always have water by my side and I run for at least 30 minutes a day. I feel a whole lot better now than I did back then. I'll see about posting some before/after photos tomorrow.
***Edit***
Before/after photos as promised.
I'm on the left. That's my brother on the right, being an idiot by sitting on my knee.
This is only a webcam shot, I don't really have any other recent photos of myself. I think you can tell that I've dropped a fair amount of weight and need to get some more sun, lol.